Background

[0001 ] A bounding volume hierarchy (BVH) may improve ray tracing algorithms. A BVH is a tree of bounding volumes enclosing objects within a scene. Ray tracing generates images by tracing paths of light rays through a virtual three-dimensional environment. Instead of checking ray traversal for each of a large number of objects, ray traversal may be more easily checked for a volume ("parent node") in a BVH that bounds those objects. If so, then successively smaller bounding volumes ("sibling nodes") can be tested for ray intersection.

[0002] In reduced precision bounding volume hierarchies, a local low resolution grid is selected such that the origin of the grid is aligned with a parent u axis and the dimensions of the grid are selected to be the smallest value that is a power of two and greater than the dimensions of the parent bounding box. The bounding box is quantized by computing integer offsets of the bounding box coordinates in the local grid.

[0003] A BVH with bounding volumes may be represented by axis-aligned bounding boxes that are specified using its minimum coordinate p and maximum coordinate q, where These coordinates can be compressed by

quantizing them to a local low resolution grid and decompressed as the BVH is traversed to evaluate ray-scene intersections. In the following, the components of a point p are accessed as p

[0004] be the corresponding coordinates of the quantized

bounding box. The next step is to encode children box inside the parent. Since the BVH compression is lossy, the decompressed coordinates can be different from the unquantized coordinates. The local low resolution grid is selected such that the origin of the grid is aligned with and the dimensions of the grid are selected to

be the smallest value that is a power of two and greater than the parent bounding box. The quantized bounding box is derived by computing relative offsets of the bounding box coordinates to the origin of the grid and quantizing the result to a small number of bits, N _b . For an axis i, these operations are described by: where is the grid dimension along x and are the quantized offsets relative to the quantized parent bounding box. Using floor rounding mode guarantees that The exponent is given by:

[0005] The bounding boxes can be iteratively decompressed from the quantized coordinates when the BVH is traversed from the root node as described in Equations 3 and 4:

where (u, v) are the decomposed coordinates that are initialized with the full precision coordinates of the root node at the start of the traversal. The value of is incremented by one, which compensates for the negative error introduced by the rightmost floor operation in Equation 1 . This also guarantees which is

required for deterministic grid dimensions if a parent node is decompressed from a child node.

[0006] Intersections between rays and the compressed BVH can be determined by traversing the BVH, decompressing the node bounding boxes and computing ray- bounding box intersections, which can be evaluated using Kay and Kajiya's slab test. This test computes three distance intervals along the ray to pairs of planes called slabs which define faces of the bounding box. The slab test uses a parameterized ray representation o+td, where o is the ray origin, d is the ray direction and t is the parametric distance along the ray. A pair of parametric distances is computed along each axis i: where is the ray slope. Parametric distances corresponding to the y and z

axes can be computed similarly. Assuming the slopes are positive, a ray

intersects the bounding box if,

[0007] where are the maximum and minimum values of _t and

respectively and represent the clip distances of the ray. The function

ulp() returns the unit in the last place of a finite precision floating-point value. Adding this compensation term guarantees watertight intersection results. If a slope is negative, the corresponding values of have to be swapped.

[0008] The slab tests can be performed with reduced precision arithmetic if the origin of the ray is moved closer to the bounding box after each traversal step. This can be done by updating the origin of the ray after each traversal step. However, if the ray origin is modified, the values of computed for the parent node cannot be reused for the child nodes. Therefore, for a pair of sibling nodes, Equations 5 and 6 have to evaluated for each of the twelve bounding planes, doubling the number of computations.

Brief Description Of The Drawings

[0009] Some embodiments are described with respect to the following figures:

Figure 1 is a depiction of a local grid for a compression scheme according to one embodiment;

Figure 2 is a flow chart for bounding volume hierarchy encoding according to one embodiment;

Figure 3 is a flow chart for computing ray-bounding volume hierarchy intersections according to one embodiment;

Figure 4 is a depiction of a pair of sibling nodes that are compressed and stored together according to one embodiment;

Figure 5 is a block diagram of a processing system according to one embodiment;

Figure 6 is a block diagram of a processor according to one embodiment; Figure 7 is a block diagram of a graphics processor according to one embodiment;

Figure 8 is a block diagram of a graphics processing engine according to one embodiment;

Figure 9 is a block diagram of another embodiment of a graphics processor; Figure 10 is a depiction of thread execution logic according to one

embodiment;

Figure 1 1 is a block diagram of a graphics processor instruction format according to some embodiments;

Figure 12 is a block diagram of another embodiment of a graphics processor;

Figure 13A is a block diagram of a graphics processor command format according to some embodiments;

Figure 13B is a block diagram illustrating a graphics processor command sequence according to some embodiments;

Figure 14 is a depiction of an exemplary graphics software architecture according to some embodiments;

Figure 15 is a block diagram illustrating an IP core development system according to some embodiments;

Figure 16 is a block diagram showing an exemplary system on chip integrated circuit according to some embodiments;

Figure 17 is a block diagram of a graphics processor in a system on a chip according to one embodiment; and

Figure 18 is a block diagram of another graphics processor according to one embodiment.

Detailed Description

[0010] Reduced precision Bounding Volume Hierarchies (BVH) and ray traversal enable high performance real time ray tracing through low cost, fixed function hardware in some embodiments. The computational cost of ray traversal can be reduced by reusing ray-box intersection computations for the six bounding planes that are shared between a parent BVH node and its two children. Unfortunately, with previous reduced precision traversal methods, this reuse is not possible.

[001 1 ] Watertight intersection (i.e. without cracks) in ray traversal algorithms is especially important with reduced precision ray traversal where numerical errors can be larger, resulting in missed intersections. A reduced precision traversal algorithm enables reuse of computations for bounding planes shared between a parent node and its children and guarantees watertight intersections, in some embodiments.

[0012] The bounding boxes of a pair of sibling nodes share six bounding planes (coordinates) with the parent node. By leveraging this, the bounds (in a binary tree) for a pair of sibling nodes can be stored together with six quantized offsets and a pair of 3-bit masks (I, m) that assign coordinates to the left or right sibling. Assuming a depth-first layout for a binary tree, one bit is stored to indicate an internal or leaf node, six compressed coordinates for the pair of sibling nodes, a pair of 3-bit masks and an N _p -bit index to the right child pair as shown in Table 1 . If the index of the right child pair is relative to the parent node, then this index is always even and the least significant bit of the index can be dropped. Therefore, If N _p is the number of bits used for the child index, a single BVH can contain nodes. Assuming

only 8 bytes are required to store a pair of nodes.

[0013] By combining bounding box decompression with traversal, a reduced precision traversal algorithm can reuse computations for planes that are shared with the parent node. This combined traversal method iteratively accumulates the parametric distances with respect to the parent node:

Since r _t is a reduced precision term, the multiplication operations in Equations 8 and 9 can be computed with reduced precision. The precision of the slope s _i can be reduced by a small amount to further lower the arithmetic complexity. The BVH quantization scheme may be modified to enable watertight intersections.

[0014] With this traversal algorithm, the decompressed bounding boxes are no longer available. Therefore the exponent _e parent cannot be directly computed. A low cost method for computing exponents avoids decompressing the bounding boxes.

[0015] With each traversal step, numerical errors can be introduced, through finite precision floating point arithmetic, which results in a lower bound and

an upper bound for the parametric distances. Assuming the slope

wi is positive, a necessary and sufficient condition for watertight intersections is that for each axis The upper bound for after the first

traversal step can be derived from Equation 9:

where ε is the machine epsilon of the underlying floating point representation and errors are introduced by the computation of the slope w the inner multiplication and

the outer addition. The value of can be derived from the leftmost expression

in Equation 1 :

[0016] Working backwards from Equation 12, the first step or criterion towards watertight intersections is to ensure that as shown in block 16, by

modifying Equation 3: where RU() rounds the result of the floating point operations to the upper value as specified in the IEEE Standard for Floating-Point Arithmetic (IEEE 754). With fixed function ray traversal, the floating point hardware can be statically configured for this rounding mode. Next the is made to be less than or equal to r _t by modifying Equation 1 : where RL() rounds the result of the floating point operations to the lower value as specified in the IEEE 754 standard. Finally \s made to be less than or equal to

where the slope w _t is also rounded to the lower value. Therefore, the first constraint for watertight intersections is met.

[0017] Although positive errors in the value of X are eliminated, negative errors still

remain. Moreover, these negative errors get accumulated with each traversal step. Unfortunately, since the offset for is derived with respect to errors in X are

coupled with the errors in u _t . Therefore, accumulated negative errors in would

lower the value of violating a second constraint for watertightness. To

compensate for this error, an accumulated correction term, would have to be

applied, introducing additional arithmetic complexity.

[0018] However, one can decouple and using an alternative compression

where offsets for are derived with respect to as shown in Figure 1.

Negative numerical errors in can then be independently eliminated similar to

positive errors in Algorithm 1 describes the compression part and Algorithm 2

describes the traversal part of this watertight traversal technique. The parametric distances are then compared to determine ray-box intersections for the sibling nodes as described in Equation 7. [0019] The sequence 10 shown in Figure 2 may be implemented in software, firmware and/or hardware. In software and firmware embodiments it may be implemented by computer executed instructions stored in one or more non-transitory computer readable media such as magnetic, optical or semiconductor storages. These storages may be part of a graphics processing unit in one embodiment or external to a graphics processing unit in another embodiment. Other embodiments are also contemplated.

[0020] The sequence 10 shown in Figure 2 begins with building an acceleration structure based on the input geometry composed of a set of primitives, typically triangles as indicated in block 12. The bounding volume hierarchy begins with a root node and ends with a leaf node. Each root node is split into a pair of child or sibling nodes and then each of those nodes is split again and again down to the leaf node. For each pair of child nodes, there is a set of minimum coordinates p in three dimensions and a set of maximum coordinates q in three dimensions. Each dimension is considered a plane.

[0021 ] For the minimum node coordinates, as indicated at 14, a sequence composed of blocks 16 through 20 is implemented. The coordinates of the child nodes that are different from their parent nodes coordinates are determined at block 16. Then the difference from their parent nodes for each of those coordinates is calculated in block 18. Significantly, this difference is determined by unencoding the parent node coordinates. Finally, the differences between the unencoded parent node coordinates and the child node coordinates is quantized as indicated in block 20.

[0022] Only the differences for coordinates that are different are stored in one embodiment. For the coordinates that are the same as the parent node coordinates, a bit mask is identified which references the parent coordinate information so that child coordinates that are same as parent coordinates do not need to be re-stored again for the child nodes.

[0023] Thus, the minimum coordinates of the child node are encoded with respect to the minimum coordinates of the parent and the maximum coordinates of the child node is encoded with respect to the maximum coordinates of the parent. This achieves water tight intersections. Using the decompressed coordinates of the parent to compute the offsets for the child coordinate results in a tighter bound as the errors introduced in the parent node are compensated while encoding the child node. Another way to achieve tighter bounds is to compute the offsets for the child with respect to the original coordinates of the parent node.

[0024] Then, as indicated in block 22, the sequence of blocks 16, 18, and 20 is repeated for the maximum coordinates. At the end, only the coordinates that are different are stored together with a bit mask that identifies, for child coordinates that are the same as parent coordinates, where to reuse, for the child node the

coordinate information from the parent node. Pseudo code 1 , set forth below, may be used for the bounding volume hierarchy compression.

[0025] At each stage, moving downwardly through the tree from the root node to the leaf node, the child node planes are either the same size or smaller than the parent node planes. Thus, the bounding boxes do not grow. So to quantize the bounding volume hierarchy as it descends with respect to the parent, the differences tend to be small and therefore the size of the data that is stored can be reduced.

[0026] For the minimum coordinates, a difference r is calculated and for the maximum coordinates, a difference s is calculated. If the child's coordinates are different from the parent's coordinates, then a variable li is set equal to one and otherwise is set equal to zero, indicating how the information will be stored. At the end the child u, v coordinates are calculated.

[0027] The r and s differences are calculated by rounding lower (RL). The child coordinate u is calculated by adding a parent coordinate to r times a factor and rounding up (RU). The child coordinate v is calculated by rounding lower (RL) the difference between the parent node coordinate and s times a factor. The number of bits is indicated as N _b in the pseudo code 1 set forth below. Thus in some

embodiments, although there are twelve coordinates for the minimum and maximum coordinates, only six must actually be stored. [0028] Pseudo Code 1 , set forth below, shows a bounding box compression for a pair of sibling nodes with decoupled minimum and maximum coordinates. Bounding box coordinates that are not shared with the parent box are indicated by a pair of three bit masks:

[0029] A sequence 30, shown in Figure 3 for performing ray primitive intersection tests may be implemented in software, firmware and/or hardware. In software and firmware embodiments it may be implemented by computer executed instructions stored in one or more non-transitory computer readable such as magnetic, optical or semiconductor storage. For example the sequence may be stored within a graphics processing unit or without, namely within an external storage. Other embodiments are also contemplated.

[0030] The sequence 30 bounding volume traversal begins by determining where a ray enters a bounding box using as indicated in block 32. Then the flow determines where the ray exits the bounding box using to get μ _i as indicated in block 34.

[0031 ] In block 36, are compared to determine a ray/bounding box

intersection by multiplying ray slope and X and ray slope and using reduced

precision multiplication.

[0032] The ray-primitive intersection test reuses the distances r and s described above in connection with pseudo code 1 . This reuse of the distances from the ray origin to each plane of minimum and maximum coordinates is a form of plane reuse that substantially reduces computations in some embodiments. The values r and s are stored in connection with the bounding volume encoding and are stored within the bounding volume hierarchy itself so that they can be accessed during the intersection test in one embodiment.

[0033] Through the use of bounding volume hierarchies for ray-primitive

intersections, the test may be performed more efficiently since it is possible to cull certain primitives that will never be intersected by a ray. The traversal starts at the root of the bounding volume hierarchy and starts intersecting a ray with the root's bounding box. If there is no intersection, then the traversal stops because there can be no intersection. If the root is intersected then the test moves on to each of the child nodes. The traversal stops at any child node that a ray does not intersect and only proceeds to descend through the hierarchy via a child node that does have a ray intersection. Eventually the leaf node is intersected and the leaf node corresponds to the primitive itself.

[0034] By computing the terms of the child bounding boxes relative to the parent bounding boxes, considerable savings can be achieved in terms of storage bandwidth in some embodiments. By reusing the values r and s from the encoding process, additional savings can be made in some embodiments.

[0035] Moreover, each successive node is tested incrementally as the flow descends down the tree. Calculations are only done for planes that are not shared with parent planes and for planes that are not shared, only certain terms are computed using the offsets r and s as already described. [0036] In a traditional traversal, a ray has an origin and direction. The distances to the six planes are computed as defined by the coordinates of the bounding boxes. Then those distances are used to determine if the ray intersects the box.

[0037] In the pseudo code 2 below, λ and μ are the distances from the origin to each of the six planes. Instead of computing absolute distances, the maximum distances to the minimum coordinates are computed to get three distances. These are the distances at which the ray enters the bounding box. Then the minimum distances to the maximum coordinates are computed to get three distances which distances are the distances at which the ray exits the box. Then the entry and exit distances are compared to determine whether any intersection occurs. If a distance that the ray enters the box is less than a distance that the ray exits the box, then the ray intersects the bounding box and otherwise there is no intersection.

[0038] The distances can be computed just like the offsets were computed above, namely using the exact same values r and s used in the pseudo code 1 . By computing the distances relative to the parent bounding box, smaller distances may be obtained which allows the use of reduced precision multiplication. Then λ and μ may be calculated using the r and s offset values already calculated. As a result, values may be multiplied, using reduced precision multiplication, by the ray's slope

[0039] Pseudo Code 2, set forth below, shows watertight traversal for a pair of sibling nodes. If the ray's slope is negative, the minimum and maximum

coordinates are swapped. Six parametric distances are computed and then assigned to the left or right child depending on the mask (I, m): for all

[0040] The grid size d _i along an axis / can be determined by computing the distance d _i between the minimum and maximum decompressed coordinates in the local grid. Since the decompressed coordinates are quantized, can be an N

unsigned floating point number. At each traversal step, the value ofd _i can be iteratively derived from its previous value

The exponent of d gives the new grid exponent i.e. The initial value of the grid size and the quantized coordinates of the root bounding box

may be pre-computed during BVH compression. [0041 ] In order to share bounding planes and traversal computations between a parent node and its children, the BVH may be traversed in a topological order, i.e. , a parent node may be traversed before its children. Typically, such a traversal would require a stack, where each stack entry would store the traversal state for the parent node, which includes the values of and d as well as the index of the far child

as shown in Figure 4. Storing the full precision values of and significantly

increases the size of a stack entry compared to an uncompressed BVH, where only the index of the child node has to be stored.

[0042] For each ray-BVH intersection, the values of the parametric distances

are initialized by performing a full precision intersection test with the quantized root bounding box. The initial parametric distances and the ray slope are only computed once per ray in one embodiment and therefore can be evaluated in the shader before initiating hardware based traversal. The computed ray slopes can also be used for watertight ray-triangle intersections.

[0043] If a component of the ray direction along an axis i is zero, then the corresponding values of evaluate to and therefore cannot be derived

incrementally. In such a scenario, the axis i is marked as a degenerate axis and instead of incrementally computing the values of ( the offset of the plane

coordinates is incrementally computed relative to the ray origin

That is equivalent to incrementally computing the value of

Once these coordinate offsets have been derived, they can be directly compared against the ray origin to derive the values of

[0044] Figure 5 is a block diagram of a processing system 100, according to an embodiment. In various embodiments the system 100 includes one or more processors 102 and one or more graphics processors 108, and may be a single processor desktop system, a multiprocessor workstation system, or a server system having a large number of processors 102 or processor cores 107. In one

embodiment, the system 100 is a processing platform incorporated within a system- on-a-chip (SoC) integrated circuit for use in mobile, handheld, or embedded devices.

[0045] An embodiment of system 100 can include, or be incorporated within a server- based gaming platform, a game console, including a game and media console, a mobile gaming console, a handheld game console, or an online game console. In some embodiments system 100 is a mobile phone, smart phone, tablet computing device or mobile Internet device. Data processing system 100 can also include, couple with, or be integrated within a wearable device, such as a smart watch wearable device, smart eyewear device, augmented reality device, or virtual reality device. In some embodiments, data processing system 100 is a television or set top box device having one or more processors 102 and a graphical interface generated by one or more graphics processors 108.

[0046] In some embodiments, the one or more processors 102 each include one or more processor cores 107 to process instructions which, when executed, perform operations for system and user software. In some embodiments, each of the one or more processor cores 107 is configured to process a specific instruction set 109. In some embodiments, instruction set 109 may facilitate Complex Instruction Set Computing (CISC), Reduced Instruction Set Computing (RISC), or computing via a Very Long Instruction Word (VLIW). Multiple processor cores 107 may each process a different instruction set 109, which may include instructions to facilitate the emulation of other instruction sets. Processor core 107 may also include other processing devices, such a Digital Signal Processor (DSP).

[0047] In some embodiments, the processor 102 includes cache memory 104.

Depending on the architecture, the processor 102 can have a single internal cache or multiple levels of internal cache. In some embodiments, the cache memory is shared among various components of the processor 102. In some embodiments, the processor 102 also uses an external cache (e.g., a Level-3 (L3) cache or Last Level Cache (LLC)) (not shown), which may be shared among processor cores 107 using known cache coherency techniques. A register file 106 is additionally included in processor 102 which may include different types of registers for storing different types of data (e.g., integer registers, floating point registers, status registers, and an instruction pointer register). Some registers may be general-purpose registers, while other registers may be specific to the design of the processor 102.

[0048] In some embodiments, processor 102 is coupled with a processor bus 1 10 to transmit communication signals such as address, data, or control signals between processor 102 and other components in system 100. In one embodiment the system 100 uses an exemplary 'hub' system architecture, including a memory controller hub 1 16 and an Input Output (I/O) controller hub 130. A memory controller hub 1 16 facilitates communication between a memory device and other components of system 100, while an I/O Controller Hub (ICH) 130 provides connections to I/O devices via a local I/O bus. In one embodiment, the logic of the memory controller hub 1 16 is integrated within the processor.

[0049] Memory device 120 can be a dynamic random access memory (DRAM) device, a static random access memory (SRAM) device, flash memory device, phase-change memory device, or some other memory device having suitable performance to serve as process memory. In one embodiment the memory device 120 can operate as system memory for the system 100, to store data 122 and instructions 121 for use when the one or more processors 102 executes an application or process. Memory controller hub 1 16 also couples with an optional external graphics processor 1 12, which may communicate with the one or more graphics processors 108 in processors 102 to perform graphics and media operations.

[0050] In some embodiments, ICH 130 enables peripherals to connect to memory device 120 and processor 102 via a high-speed I/O bus. The I/O peripherals include, but are not limited to, an audio controller 146, a firmware interface 128, a wireless transceiver 126 (e.g., Wi-Fi, Bluetooth), a data storage device 124 (e.g., hard disk drive, flash memory, etc.), and a legacy I/O controller 140 for coupling legacy (e.g., Personal System 2 (PS/2)) devices to the system. One or more Universal Serial Bus (USB) controllers 142 connect input devices, such as keyboard and mouse 144 combinations. A network controller 134 may also couple with ICH 130. In some embodiments, a high-performance network controller (not shown) couples with processor bus 1 10. It will be appreciated that the system 100 shown is exemplary and not limiting, as other types of data processing systems that are differently configured may also be used. For example, the I/O controller hub 130 may be integrated within the one or more processor 102, or the memory controller hub 1 16 and I/O controller hub 130 may be integrated into a discreet external graphics processor, such as the external graphics processor 1 12.

[0051 ] Figure 6 is a block diagram of an embodiment of a processor 200 having one or more processor cores 202A-202N, an integrated memory controller 214, and an integrated graphics processor 208. Those elements of Figure 6 having the same reference numbers (or names) as the elements of any other figure herein can operate or function in any manner similar to that described elsewhere herein, but are not limited to such. Processor 200 can include additional cores up to and including additional core 202N represented by the dashed lined boxes. Each of processor cores 202A-202N includes one or more internal cache units 204A-204N. In some embodiments each processor core also has access to one or more shared cached units 206.

[0052] The internal cache units 204A-204N and shared cache units 206 represent a cache memory hierarchy within the processor 200. The cache memory hierarchy may include at least one level of instruction and data cache within each processor core and one or more levels of shared mid-level cache, such as a Level 2 (L2), Level 3 (L3), Level 4 (L4), or other levels of cache, where the highest level of cache before external memory is classified as the LLC. In some embodiments, cache coherency logic maintains coherency between the various cache units 206 and 204A-204N.

[0053] In some embodiments, processor 200 may also include a set of one or more bus controller units 216 and a system agent core 210. The one or more bus controller units 216 manage a set of peripheral buses, such as one or more

Peripheral Component Interconnect buses (e.g., PCI, PCI Express). System agent core 210 provides management functionality for the various processor components. In some embodiments, system agent core 210 includes one or more integrated memory controllers 214 to manage access to various external memory devices (not shown).

[0054] In some embodiments, one or more of the processor cores 202A-202N include support for simultaneous multi-threading. In such embodiment, the system agent core 210 includes components for coordinating and operating cores 202A- 202N during multi-threaded processing. System agent core 210 may additionally include a power control unit (PCU), which includes logic and components to regulate the power state of processor cores 202A-202N and graphics processor 208.

[0055] In some embodiments, processor 200 additionally includes graphics processor 208 to execute graphics processing operations. In some embodiments, the graphics processor 208 couples with the set of shared cache units 206, and the system agent core 210, including the one or more integrated memory controllers 214. In some embodiments, a display controller 21 1 is coupled with the graphics processor 208 to drive graphics processor output to one or more coupled displays. In some embodiments, display controller 21 1 may be a separate module coupled with the graphics processor via at least one interconnect, or may be integrated within the graphics processor 208 or system agent core 210.

[0056] In some embodiments, a ring based interconnect unit 212 is used to couple the internal components of the processor 200. However, an alternative interconnect unit may be used, such as a point-to-point interconnect, a switched interconnect, or other techniques, including techniques well known in the art. In some embodiments, graphics processor 208 couples with the ring interconnect 212 via an I/O link 213.

[0057] The exemplary I/O link 213 represents at least one of multiple varieties of I/O interconnects, including an on package I/O interconnect which facilitates

communication between various processor components and a high-performance embedded memory module 218, such as an eDRAM module. In some

embodiments, each of the processor cores 202A-202N and graphics processor 208 use embedded memory modules 218 as a shared Last Level Cache.

[0058] In some embodiments, processor cores 202A-202N are homogenous cores executing the same instruction set architecture. In another embodiment, processor cores 202A-202N are heterogeneous in terms of instruction set architecture (ISA), where one or more of processor cores 202A-202N execute a first instruction set, while at least one of the other cores executes a subset of the first instruction set or a different instruction set. In one embodiment processor cores 202A-202N are heterogeneous in terms of microarchitecture, where one or more cores having a relatively higher power consumption couple with one or more power cores having a lower power consumption. Additionally, processor 200 can be implemented on one or more chips or as an SoC integrated circuit having the illustrated components, in addition to other components.

[0059] Figure 7 is a block diagram of a graphics processor 300, which may be a discrete graphics processing unit, or may be a graphics processor integrated with a plurality of processing cores. In some embodiments, the graphics processor communicates via a memory mapped I/O interface to registers on the graphics processor and with commands placed into the processor memory. In some embodiments, graphics processor 300 includes a memory interface 314 to access memory. Memory interface 314 can be an interface to local memory, one or more internal caches, one or more shared external caches, and/or to system memory.

[0060] In some embodiments, graphics processor 300 also includes a display controller 302 to drive display output data to a display device 320. Display controller 302 includes hardware for one or more overlay planes for the display and

composition of multiple layers of video or user interface elements. In some embodiments, graphics processor 300 includes a video codec engine 306 to encode, decode, or transcode media to, from, or between one or more media encoding formats, including, but not limited to Moving Picture Experts Group (MPEG) formats such as MPEG-2, Advanced Video Coding (AVC) formats such as H.264/MPEG-4 AVC, as well as the Society of Motion Picture & Television Engineers (SMPTE) 421 M/VC-1 , and Joint Photographic Experts Group (JPEG) formats such as JPEG, and Motion JPEG (MJPEG) formats.

[0061 ] In some embodiments, graphics processor 300 includes a block image transfer (BLIT) engine 304 to perform two-dimensional (2D) rasterizer operations including, for example, bit-boundary block transfers. However, in one embodiment, 2D graphics operations are performed using one or more components of graphics processing engine (GPE) 310. In some embodiments, GPE 310 is a compute engine for performing graphics operations, including three-dimensional (3D) graphics operations and media operations.

[0062] In some embodiments, GPE 310 includes a 3D pipeline 312 for performing 3D operations, such as rendering three-dimensional images and scenes using processing functions that act upon 3D primitive shapes (e.g., rectangle, triangle, etc.). The 3D pipeline 312 includes programmable and fixed function elements that perform various tasks within the element and/or spawn execution threads to a 3D/Media sub-system 315. While 3D pipeline 312 can be used to perform media operations, an embodiment of GPE 310 also includes a media pipeline 316 that is specifically used to perform media operations, such as video post-processing and image enhancement.

[0063] In some embodiments, media pipeline 316 includes fixed function or programmable logic units to perform one or more specialized media operations, such as video decode acceleration, video de-interlacing, and video encode acceleration in place of, or on behalf of video codec engine 306. In some embodiments, media pipeline 316 additionally includes a thread spawning unit to spawn threads for execution on 3D/Media sub-system 315. The spawned threads perform

computations for the media operations on one or more graphics execution units included in 3D/Media sub-system 315.

[0064] In some embodiments, 3D/Media subsystem 315 includes logic for executing threads spawned by 3D pipeline 312 and media pipeline 316. In one embodiment, the pipelines send thread execution requests to 3D/Media subsystem 315, which includes thread dispatch logic for arbitrating and dispatching the various requests to available thread execution resources. The execution resources include an array of graphics execution units to process the 3D and media threads. In some

embodiments, 3D/Media subsystem 315 includes one or more internal caches for thread instructions and data. In some embodiments, the subsystem also includes shared memory, including registers and addressable memory, to share data between threads and to store output data. [0065] Figure 8 is a block diagram of a graphics processing engine 410 of a graphics processor in accordance with some embodiments. In one embodiment, the graphics processing engine (GPE) 410 is a version of the GPE 310 shown in Figure 7.

Elements of Figure 8 having the same reference numbers (or names) as the elements of any other figure herein can operate or function in any manner similar to that described elsewhere herein, but are not limited to such. For example, the 3D pipeline 312 and media pipeline 316 of Figure 7 are illustrated. The media pipeline 316 is optional in some embodiments of the GPE 410 and may not be explicitly included within the GPE 410. For example and in at least one embodiment, a separate media and/or image processor is coupled to the GPE 410.

[0066] In some embodiments, GPE 410 couples with or includes a command streamer 403, which provides a command stream to the 3D pipeline 312 and/or media pipelines 316. In some embodiments, command streamer 403 is coupled with memory, which can be system memory, or one or more of internal cache memory and shared cache memory. In some embodiments, command streamer 403 receives commands from the memory and sends the commands to 3D pipeline 312 and/or media pipeline 316. The commands are directives fetched from a ring buffer, which stores commands for the 3D pipeline 312 and media pipeline 316. In one embodiment, the ring buffer can additionally include batch command buffers storing batches of multiple commands. The commands for the 3D pipeline 312 can also include references to data stored in memory, such as but not limited to vertex and geometry data for the 3D pipeline 312 and/or image data and memory objects for the media pipeline 316. The 3D pipeline 312 and media pipeline 316 process the commands and data by performing operations via logic within the respective pipelines or by dispatching one or more execution threads to a graphics core array 414.

[0067] In various embodiments the 3D pipeline 312 can execute one or more shader programs, such as vertex shaders, geometry shaders, pixel shaders, fragment shaders, compute shaders, or other shader programs, by processing the instructions and dispatching execution threads to the graphics core array 414. The graphics core array 414 provides a unified block of execution resources. Multi-purpose execution logic (e.g., execution units) within the graphic core array 414 includes support for various 3D API shader languages and can execute multiple simultaneous execution threads associated with multiple shaders.

[0068] In some embodiments the graphics core array 414 also includes execution logic to perform media functions, such as video and/or image processing. In one embodiment, the execution units additionally include general-purpose logic that is programmable to perform parallel general purpose computational operations, in addition to graphics processing operations. The general purpose logic can perform processing operations in parallel or in conjunction with general purpose logic within the processor core(s) 107 of Figure 5 or core 202A-202N as in Figure 6.

[0069] Output data generated by threads executing on the graphics core array 414 can output data to memory in a unified return buffer (URB) 418. The URB 418 can store data for multiple threads. In some embodiments the URB 418 may be used to send data between different threads executing on the graphics core array 414. In some embodiments the URB 418 may additionally be used for synchronization between threads on the graphics core array and fixed function logic within the shared function logic 420.

[0070] In some embodiments, graphics core array 414 is scalable, such that the array includes a variable number of graphics cores, each having a variable number of execution units based on the target power and performance level of GPE 410. In one embodiment the execution resources are dynamically scalable, such that execution resources may be enabled or disabled as needed.

[0071 ] The graphics core array 414 couples with shared function logic 420 that includes multiple resources that are shared between the graphics cores in the graphics core array. The shared functions within the shared function logic 420 are hardware logic units that provide specialized supplemental functionality to the graphics core array 414. In various embodiments, shared function logic 420 includes but is not limited to sampler 421 , math 422, and inter-thread communication (ITC) 423 logic. Additionally, some embodiments implement one or more cache(s) 425 within the shared function logic 420. A shared function is implemented where the demand for a given specialized function is insufficient for inclusion within the graphics core array 414. Instead a single instantiation of that specialized function is implemented as a stand-alone entity in the shared function logic 420 and shared among the execution resources within the graphics core array 414. The precise set of functions that are shared between the graphics core array 414 and included within the graphics core array 414 varies between embodiments.

[0072] Figure 9 is a block diagram of another embodiment of a graphics processor 500. Elements of Figure 9 having the same reference numbers (or names) as the elements of any other figure herein can operate or function in any manner similar to that described elsewhere herein, but are not limited to such.

[0073] In some embodiments, graphics processor 500 includes a ring interconnect 502, a pipeline front-end 504, a media engine 537, and graphics cores 580A-580N. In some embodiments, ring interconnect 502 couples the graphics processor to other processing units, including other graphics processors or one or more general- purpose processor cores. In some embodiments, the graphics processor is one of many processors integrated within a multi-core processing system.

[0074] In some embodiments, graphics processor 500 receives batches of

commands via ring interconnect 502. The incoming commands are interpreted by a command streamer 503 in the pipeline front-end 504. In some embodiments, graphics processor 500 includes scalable execution logic to perform 3D geometry processing and media processing via the graphics core(s) 580A-580N. For 3D geometry processing commands, command streamer 503 supplies commands to geometry pipeline 536. For at least some media processing commands, command streamer 503 supplies the commands to a video front end 534, which couples with a media engine 537. In some embodiments, media engine 537 includes a Video Quality Engine (VQE) 530 for video and image post-processing and a multi-format encode/decode (MFX) 533 engine to provide hardware-accelerated media data encode and decode. In some embodiments, geometry pipeline 536 and media engine 537 each generate execution threads for the thread execution resources provided by at least one graphics core 580A. [0075] In some embodiments, graphics processor 500 includes scalable thread execution resources featuring modular cores 580A-580N (sometimes referred to as core slices), each having multiple sub-cores 550A-550N, 560A-560N (sometimes referred to as core sub-slices). In some embodiments, graphics processor 500 can have any number of graphics cores 580A through 580N. In some embodiments, graphics processor 500 includes a graphics core 580A having at least a first sub- core 550A and a second sub-core 560A. In other embodiments, the graphics processor is a low power processor with a single sub-core (e.g., 550A). In some embodiments, graphics processor 500 includes multiple graphics cores 580A-580N, each including a set of first sub-cores 550A-550N and a set of second sub-cores 560A-560N. Each sub-core in the set of first sub-cores 550A-550N includes at least a first set of execution units 552A-552N and media/texture samplers 554A-554N. Each sub-core in the set of second sub-cores 560A-560N includes at least a second set of execution units 562A-562N and samplers 564A-564N. In some embodiments, each sub-core 550A-550N, 560A-560N shares a set of shared resources 570A- 570N. In some embodiments, the shared resources include shared cache memory and pixel operation logic. Other shared resources may also be included in the various embodiments of the graphics processor.

[0076] Figure 10 illustrates thread execution logic 600 including an array of processing elements employed in some embodiments of a GPE. Elements of Figure 10 having the same reference numbers (or names) as the elements of any other figure herein can operate or function in any manner similar to that described elsewhere herein, but are not limited to such.

[0077] In some embodiments, thread execution logic 600 includes a shader processor 602, a thread dispatcher 604, instruction cache 606, a scalable execution unit array including a plurality of execution units 608A-608N, a sampler 610, a data cache 612, and a data port 614. In one embodiment the scalable execution unit array can dynamically scale by enabling or disabling one or more execution units (e.g., any of execution unit 608A, 608B, 608C, 608D, through 608N-1 and 608N) based on the computational requirements of a workload. In one embodiment the included components are interconnected via an interconnect fabric that links to each of the components. In some embodiments, thread execution logic 600 includes one or more connections to memory, such as system memory or cache memory, through one or more of instruction cache 606, data port 614, sampler 610, and execution units 608A-608N. In some embodiments, each execution unit (e.g. 608A) is a standalone programmable general purpose computational unit that is capable of executing multiple simultaneous hardware threads while processing multiple data elements in parallel for each thread. In various embodiments, the array of execution units 608A- 608N is scalable to include any number individual execution units.

[0078] In some embodiments, the execution units 608A-608N are primarily used to execute shader programs. A shader processor 602 can process the various shader programs and dispatch execution threads associated with the shader programs via a thread dispatcher 604. In one embodiment the thread dispatcher includes logic to arbitrate thread initiation requests from the graphics and media pipelines and instantiate the requested threads on one or more execution unit in the execution units 608A-608N. For example, the geometry pipeline (e.g., 536 of Figure 9) can dispatch vertex, tessellation, or geometry shaders to the thread execution logic 600 (Figure 10) for processing. In some embodiments, thread dispatcher 604 can also process runtime thread spawning requests from the executing shader programs.

[0079] In some embodiments, the execution units 608A-608N support an instruction set that includes native support for many standard 3D graphics shader instructions, such that shader programs from graphics libraries (e.g., Direct 3D and OpenGL) are executed with a minimal translation. The execution units support vertex and geometry processing (e.g., vertex programs, geometry programs, vertex shaders), pixel processing (e.g., pixel shaders, fragment shaders) and general-purpose processing (e.g., compute and media shaders). Each of the execution units 608A- 608N is capable of multi-issue single instruction multiple data (SIMD) execution and multi-threaded operation enables an efficient execution environment in the face of higher latency memory accesses. Each hardware thread within each execution unit has a dedicated high-bandwidth register file and associated independent thread- state. Execution is multi-issue per clock to pipelines capable of integer, single and double precision floating point operations, SIMD branch capability, logical operations, transcendental operations, and other miscellaneous operations. While waiting for data from memory or one of the shared functions, dependency logic within the execution units 608A-608N causes a waiting thread to sleep until the requested data has been returned. While the waiting thread is sleeping, hardware resources may be devoted to processing other threads. For example, during a delay associated with a vertex shader operation, an execution unit can perform operations for a pixel shader, fragment shader, or another type of shader program, including a different vertex shader.

[0080] Each execution unit in execution units 608A-608N operates on arrays of data elements. The number of data elements is the "execution size," or the number of channels for the instruction. An execution channel is a logical unit of execution for data element access, masking, and flow control within instructions. The number of channels may be independent of the number of physical Arithmetic Logic Units (ALUs) or Floating Point Units (FPUs) for a particular graphics processor. In some embodiments, execution units 608A-608N support integer and floating-point data types.

[0081 ] The execution unit instruction set includes SIMD instructions. The various data elements can be stored as a packed data type in a register and the execution unit will process the various elements based on the data size of the elements. For example, when operating on a 256-bit wide vector, the 256 bits of the vector are stored in a register and the execution unit operates on the vector as four separate 64-bit packed data elements (Quad-Word (QW) size data elements), eight separate 32-bit packed data elements (Double Word (DW) size data elements), sixteen separate 16-bit packed data elements (Word (W) size data elements), or thirty-two separate 8-bit data elements (byte (B) size data elements). However, different vector widths and register sizes are possible.

[0082] One or more internal instruction caches (e.g., 606) are included in the thread execution logic 600 to cache thread instructions for the execution units. In some embodiments, one or more data caches (e.g., 612) are included to cache thread data during thread execution. In some embodiments, a sampler 610 is included to provide texture sampling for 3D operations and media sampling for media operations. In some embodiments, sampler 610 includes specialized texture or media sampling functionality to process texture or media data during the sampling process before providing the sampled data to an execution unit.

[0083] During execution, the graphics and media pipelines send thread initiation requests to thread execution logic 600 via thread spawning and dispatch logic. Once a group of geometric objects has been processed and rasterized into pixel data, pixel processor logic (e.g., pixel shader logic, fragment shader logic, etc.) within the shader processor 602 is invoked to further compute output information and cause results to be written to output surfaces (e.g., color buffers, depth buffers, stencil buffers, etc.). In some embodiments, a pixel shader or fragment shader calculates the values of the various vertex attributes that are to be interpolated across the rasterized object. In some embodiments, pixel processor logic within the shader processor 602 then executes an application programming interface (API)-supplied pixel or fragment shader program. To execute the shader program, the shader processor 602 dispatches threads to an execution unit (e.g., 608A) via thread dispatcher 604. In some embodiments, pixel shader 602 uses texture sampling logic in the sampler 610 to access texture data in texture maps stored in memory.

Arithmetic operations on the texture data and the input geometry data compute pixel color data for each geometric fragment, or discards one or more pixels from further processing.

[0084] In some embodiments, the data port 614 provides a memory access mechanism for the thread execution logic 600 output processed data to memory for processing on a graphics processor output pipeline. In some embodiments, the data port 614 includes or couples to one or more cache memories (e.g., data cache 612) to cache data for memory access via the data port.

[0085] Figure 11 is a block diagram illustrating a graphics processor instruction formats 700 according to some embodiments. In one or more embodiment, the graphics processor execution units support an instruction set having instructions in multiple formats. The solid lined boxes illustrate the components that are generally included in an execution unit instruction, while the dashed lines include components that are optional or that are only included in a sub-set of the instructions. In some embodiments, instruction format 700 described and illustrated are macro- instructions, in that they are instructions supplied to the execution unit, as opposed to micro-operations resulting from instruction decode once the instruction is processed.

[0086] In some embodiments, the graphics processor execution units natively support instructions in a 128-bit instruction format 710. A 64-bit compacted instruction format 730 is available for some instructions based on the selected instruction, instruction options, and number of operands. The native 128-bit instruction format 710 provides access to all instruction options, while some options and operations are restricted in the 64-bit format 730. The native instructions available in the 64-bit format 730 vary by embodiment. In some embodiments, the instruction is compacted in part using a set of index values in an index field 713. The execution unit hardware references a set of compaction tables based on the index values and uses the compaction table outputs to reconstruct a native instruction in the 128-bit instruction format 710.

[0087] For each format, instruction opcode 712 defines the operation that the execution unit is to perform. The execution units execute each instruction in parallel across the multiple data elements of each operand. For example, in response to an add instruction the execution unit performs a simultaneous add operation across each color channel representing a texture element or picture element. By default, the execution unit performs each instruction across all data channels of the operands. In some embodiments, instruction control field 714 enables control over certain execution options, such as channels selection (e.g., predication) and data channel order (e.g., swizzle). For instructions in the 128-bit instruction format 710 an exec-size field 716 limits the number of data channels that will be executed in parallel. In some embodiments, exec-size field 716 is not available for use in the 64- bit compact instruction format 730.

[0088] Some execution unit instructions have up to three operands including two source operands, srcO 720, srd 722, and one destination 718. In some

embodiments, the execution units support dual destination instructions, where one of the destinations is implied. Data manipulation instructions can have a third source operand (e.g., SRC2 724), where the instruction opcode 712 determines the number of source operands. An instruction's last source operand can be an immediate (e.g., hard-coded) value passed with the instruction.

[0089] In some embodiments, the 128-bit instruction format 710 includes an access/address mode field 726 specifying, for example, whether direct register addressing mode or indirect register addressing mode is used. When direct register addressing mode is used, the register address of one or more operands is directly provided by bits in the instruction.

[0090] In some embodiments, the 128-bit instruction format 710 includes an access/address mode field 726, which specifies an address mode and/or an access mode for the instruction. In one embodiment the access mode is used to define a data access alignment for the instruction. Some embodiments support access modes including a 16-byte aligned access mode and a 1 -byte aligned access mode, where the byte alignment of the access mode determines the access alignment of the instruction operands. For example, when in a first mode, the instruction may use byte-aligned addressing for source and destination operands and when in a second mode, the instruction may use 16-byte-aligned addressing for all source and destination operands.

[0091 ] In one embodiment, the address mode portion of the access/address mode field 726 determines whether the instruction is to use direct or indirect addressing. When direct register addressing mode is used bits in the instruction directly provide the register address of one or more operands. When indirect register addressing mode is used, the register address of one or more operands may be computed based on an address register value and an address immediate field in the

instruction.

[0092] In some embodiments instructions are grouped based on opcode 712 bitfields to simplify Opcode decode 740. For an 8-bit opcode, bits 4, 5, and 6 allow the execution unit to determine the type of opcode. The precise opcode grouping shown is merely an example. In some embodiments, a move and logic opcode group 742 includes data movement and logic instructions (e.g., move (mov), compare (cmp)). In some embodiments, move and logic group 742 shares the five most significant bits (MSB), where move (mov) instructions are in the form of OOOOxxxxb and logic instructions are in the form of 0001xxxxb. A flow control instruction group 744 (e.g., call, jump (jmp)) includes instructions in the form of 0010xxxxb (e.g., 0x20). A miscellaneous instruction group 746 includes a mix of instructions, including synchronization instructions (e.g., wait, send) in the form of 001 Ixxxxb (e.g., 0x30). A parallel math instruction group 748 includes component-wise arithmetic

instructions (e.g., add, multiply (mul)) in the form of 0100xxxxb (e.g., 0x40). The parallel math group 748 performs the arithmetic operations in parallel across data channels. The vector math group 750 includes arithmetic instructions (e.g., dp4) in the form of 0101xxxxb (e.g., 0x50). The vector math group performs arithmetic such as dot product calculations on vector operands.

[0093] Figure 12 is a block diagram of another embodiment of a graphics processor 800. Elements of Figure 12 having the same reference numbers (or names) as the elements of any other figure herein can operate or function in any manner similar to that described elsewhere herein, but are not limited to such.

[0094] In some embodiments, graphics processor 800 includes a graphics pipeline 820, a media pipeline 830, a display engine 840, thread execution logic 850, and a render output pipeline 870. In some embodiments, graphics processor 800 is a graphics processor within a multi-core processing system that includes one or more general purpose processing cores. The graphics processor is controlled by register writes to one or more control registers (not shown) or via commands issued to graphics processor 800 via a ring interconnect 802. In some embodiments, ring interconnect 802 couples graphics processor 800 to other processing components, such as other graphics processors or general-purpose processors. Commands from ring interconnect 802 are interpreted by a command streamer 803, which supplies instructions to individual components of graphics pipeline 820 or media pipeline 830.

[0095] In some embodiments, command streamer 803 directs the operation of a vertex fetcher 805 that reads vertex data from memory and executes vertex- processing commands provided by command streamer 803. In some embodiments, vertex fetcher 805 provides vertex data to a vertex shader 807, which performs coordinate space transformation and lighting operations to each vertex. In some embodiments, vertex fetcher 805 and vertex shader 807 execute vertex-processing instructions by dispatching execution threads to execution units 852A-852B via a thread dispatcher 831 .

[0096] In some embodiments, execution units 852A-852B are an array of vector processors having an instruction set for performing graphics and media operations. In some embodiments, execution units 852A-852B have an attached L1 cache 851 that is specific for each array or shared between the arrays. The cache can be configured as a data cache, an instruction cache, or a single cache that is partitioned to contain data and instructions in different partitions.

[0097] In some embodiments, graphics pipeline 820 includes tessellation

components to perform hardware-accelerated tessellation of 3D objects. In some embodiments, a programmable hull shader 81 1 configures the tessellation operations. A programmable domain shader 817 provides back-end evaluation of tessellation output. A tessellator 813 operates at the direction of hull shader 81 1 and contains special purpose logic to generate a set of detailed geometric objects based on a coarse geometric model that is provided as input to graphics pipeline 820. In some embodiments, if tessellation is not used, tessellation components (e.g., hull shader 81 1 , tessellator 813, and domain shader 817) can be bypassed.

[0098] In some embodiments, complete geometric objects can be processed by a geometry shader 819 via one or more threads dispatched to execution units 852A- 852B, or can proceed directly to the clipper 829. In some embodiments, the geometry shader operates on entire geometric objects, rather than vertices or patches of vertices as in previous stages of the graphics pipeline. If the tessellation is disabled the geometry shader 819 receives input from the vertex shader 807. In some embodiments, geometry shader 819 is programmable by a geometry shader program to perform geometry tessellation if the tessellation units are disabled.

[0099] Before rasterization, a clipper 829 processes vertex data. The clipper 829 may be a fixed function clipper or a programmable clipper having clipping and geometry shader functions. In some embodiments, a rasterizer and depth test component 873 in the render output pipeline 870 dispatches pixel shaders to convert the geometric objects into their per pixel representations. In some embodiments, pixel shader logic is included in thread execution logic 850. In some embodiments, an application can bypass the rasterizer and depth test component 873 and access un-rasterized vertex data via a stream out unit 823.

[0100] The graphics processor 800 has an interconnect bus, interconnect fabric, or some other interconnect mechanism that allows data and message passing amongst the major components of the processor. In some embodiments, execution units 852A-852B and associated cache(s) 851 , texture and media sampler 854, and texture/sampler cache 858 interconnect via a data port 856 to perform memory access and communicate with render output pipeline components of the processor. In some embodiments, sampler 854, caches 851 , 858 and execution units 852A- 852B each have separate memory access paths.

[0101 ] In some embodiments, render output pipeline 870 contains a rasterizer and depth test component 873 that converts vertex-based objects into an associated pixel-based representation. In some embodiments, the rasterizer logic includes a windower/masker unit to perform fixed function triangle and line rasterization. An associated render cache 878 and depth cache 879 are also available in some embodiments. A pixel operations component 877 performs pixel-based operations on the data, though in some instances, pixel operations associated with 2D operations (e.g. bit block image transfers with blending) are performed by the 2D engine 841 , or substituted at display time by the display controller 843 using overlay display planes. In some embodiments, a shared L3 cache 875 is available to all graphics components, allowing the sharing of data without the use of main system memory.

[0102] In some embodiments, graphics processor media pipeline 830 includes a media engine 837 and a video front end 834. In some embodiments, video front end 834 receives pipeline commands from the command streamer 803. In some embodiments, media pipeline 830 includes a separate command streamer. In some embodiments, video front-end 834 processes media commands before sending the command to the media engine 837. In some embodiments, media engine 837 includes thread spawning functionality to spawn threads for dispatch to thread execution logic 850 via thread dispatcher 831.

[0103] In some embodiments, graphics processor 800 includes a display engine 840. In some embodiments, display engine 840 is external to processor 800 and couples with the graphics processor via the ring interconnect 802, or some other interconnect bus or fabric. In some embodiments, display engine 840 includes a 2D engine 841 and a display controller 843. In some embodiments, display engine 840 contains special purpose logic capable of operating independently of the 3D pipeline. In some embodiments, display controller 843 couples with a display device (not shown), which may be a system integrated display device, as in a laptop computer, or an external display device attached via a display device connector.

[0104] In some embodiments, graphics pipeline 820 and media pipeline 830 are configurable to perform operations based on multiple graphics and media

programming interfaces and are not specific to any one application programming interface (API). In some embodiments, driver software for the graphics processor translates API calls that are specific to a particular graphics or media library into commands that can be processed by the graphics processor. In some

embodiments, support is provided for the Open Graphics Library (OpenGL), Open Computing Language (OpenCL), and/or Vulkan graphics and compute API, all from the Khronos Group. In some embodiments, support may also be provided for the Direct3D library from the Microsoft Corporation. In some embodiments, a

combination of these libraries may be supported. Support may also be provided for the Open Source Computer Vision Library (OpenCV). A future API with a compatible 3D pipeline would also be supported if a mapping can be made from the pipeline of the future API to the pipeline of the graphics processor.

[0105] Figure 13A is a block diagram illustrating a graphics processor command format 900 according to some embodiments. Figure 13B is a block diagram illustrating a graphics processor command sequence 910 according to an

embodiment. The solid lined boxes in Figure 13A illustrate the components that are generally included in a graphics command while the dashed lines include

components that are optional or that are only included in a sub-set of the graphics commands. The exemplary graphics processor command format 900 of Figure 13A includes data fields to identify a target client 902 of the command, a command operation code (opcode) 904, and the relevant data 906 for the command. A sub- opcode 905 and a command size 908 are also included in some commands.

[0106] In some embodiments, client 902 specifies the client unit of the graphics device that processes the command data. In some embodiments, a graphics processor command parser examines the client field of each command to condition the further processing of the command and route the command data to the appropriate client unit. In some embodiments, the graphics processor client units include a memory interface unit, a render unit, a 2D unit, a 3D unit, and a media unit. Each client unit has a corresponding processing pipeline that processes the commands. Once the command is received by the client unit, the client unit reads the opcode 904 and, if present, sub-opcode 905 to determine the operation to perform. The client unit performs the command using information in data field 906. For some commands an explicit command size 908 is expected to specify the size of the command. In some embodiments, the command parser automatically

determines the size of at least some of the commands based on the command opcode. In some embodiments commands are aligned via multiples of a double word.

[0107] The flow diagram in Figure 13B shows an exemplary graphics processor command sequence 910. In some embodiments, software or firmware of a data processing system that features an embodiment of a graphics processor uses a version of the command sequence shown to set up, execute, and terminate a set of graphics operations. A sample command sequence is shown and described for purposes of example only as embodiments are not limited to these specific commands or to this command sequence. Moreover, the commands may be issued as batch of commands in a command sequence, such that the graphics processor will process the sequence of commands in at least partially concurrence.

[0108] In some embodiments, the graphics processor command sequence 910 may begin with a pipeline flush command 912 to cause any active graphics pipeline to complete the currently pending commands for the pipeline. In some embodiments, the 3D pipeline 922 and the media pipeline 924 do not operate concurrently. The pipeline flush is performed to cause the active graphics pipeline to complete any pending commands. In response to a pipeline flush, the command parser for the graphics processor will pause command processing until the active drawing engines complete pending operations and the relevant read caches are invalidated.

Optionally, any data in the render cache that is marked 'dirty' can be flushed to memory. In some embodiments, pipeline flush command 912 can be used for pipeline synchronization or before placing the graphics processor into a low power state.

[0109] In some embodiments, a pipeline select command 913 is used when a command sequence requires the graphics processor to explicitly switch between pipelines. In some embodiments, a pipeline select command 913 is required only once within an execution context before issuing pipeline commands unless the context is to issue commands for both pipelines. In some embodiments, a pipeline flush command 912 is required immediately before a pipeline switch via the pipeline select command 913.

[01 10] In some embodiments, a pipeline control command 914 configures a graphics pipeline for operation and is used to program the 3D pipeline 922 and the media pipeline 924. In some embodiments, pipeline control command 914 configures the pipeline state for the active pipeline. In one embodiment, the pipeline control command 914 is used for pipeline synchronization and to clear data from one or more cache memories within the active pipeline before processing a batch of commands.

[01 1 1 ] In some embodiments, return buffer state commands 916 are used to configure a set of return buffers for the respective pipelines to write data. Some pipeline operations require the allocation, selection, or configuration of one or more return buffers into which the operations write intermediate data during processing. In some embodiments, the graphics processor also uses one or more return buffers to store output data and to perform cross thread communication. In some

embodiments, the return buffer state 916 includes selecting the size and number of return buffers to use for a set of pipeline operations. [01 12] The remaining commands in the command sequence differ based on the active pipeline for operations. Based on a pipeline determination 920, the command sequence is tailored to the 3D pipeline 922 beginning with the 3D pipeline state 930 or the media pipeline 924 beginning at the media pipeline state 940.

[01 13] The commands to configure the 3D pipeline state 930 include 3D state setting commands for vertex buffer state, vertex element state, constant color state, depth buffer state, and other state variables that are to be configured before 3D primitive commands are processed. The values of these commands are determined at least in part based on the particular 3D API in use. In some embodiments, 3D pipeline state 930 commands are also able to selectively disable or bypass certain pipeline elements if those elements will not be used.

[01 14] In some embodiments, 3D primitive 932 command is used to submit 3D primitives to be processed by the 3D pipeline. Commands and associated parameters that are passed to the graphics processor via the 3D primitive 932 command are forwarded to the vertex fetch function in the graphics pipeline. The vertex fetch function uses the 3D primitive 932 command data to generate vertex data structures. The vertex data structures are stored in one or more return buffers. In some embodiments, 3D primitive 932 command is used to perform vertex operations on 3D primitives via vertex shaders. To process vertex shaders, 3D pipeline 922 dispatches shader execution threads to graphics processor execution units.

[01 15] In some embodiments, 3D pipeline 922 is triggered via an execute 934 command or event. In some embodiments, a register write triggers command execution. In some embodiments execution is triggered via a 'go' or 'kick' command in the command sequence. In one embodiment, command execution is triggered using a pipeline synchronization command to flush the command sequence through the graphics pipeline. The 3D pipeline will perform geometry processing for the 3D primitives. Once operations are complete, the resulting geometric objects are rasterized and the pixel engine colors the resulting pixels. Additional commands to control pixel shading and pixel back end operations may also be included for those operations. [01 16] In some embodiments, the graphics processor command sequence 910 follows the media pipeline 924 path when performing media operations. In general, the specific use and manner of programming for the media pipeline 924 depends on the media or compute operations to be performed. Specific media decode operations may be offloaded to the media pipeline during media decode. In some embodiments, the media pipeline can also be bypassed and media decode can be performed in whole or in part using resources provided by one or more general purpose processing cores. In one embodiment, the media pipeline also includes elements for general-purpose graphics processor unit (GPGPU) operations, where the graphics processor is used to perform SIMD vector operations using

computational shader programs that are not explicitly related to the rendering of graphics primitives.

[01 17] In some embodiments, media pipeline 924 is configured in a similar manner as the 3D pipeline 922. A set of commands to configure the media pipeline state 940 are dispatched or placed into a command queue before the media object commands 942. In some embodiments, media pipeline state commands 940 include data to configure the media pipeline elements that will be used to process the media objects. This includes data to configure the video decode and video encode logic within the media pipeline, such as encode or decode format. In some embodiments, media pipeline state commands 940 also support the use of one or more pointers to "indirect" state elements that contain a batch of state settings.

[01 18] In some embodiments, media object commands 942 supply pointers to media objects for processing by the media pipeline. The media objects include memory buffers containing video data to be processed. In some embodiments, all media pipeline states must be valid before issuing a media object command 942. Once the pipeline state is configured and media object commands 942 are queued, the media pipeline 924 is triggered via an execute command 944 or an equivalent execute event (e.g., register write). Output from media pipeline 924 may then be post processed by operations provided by the 3D pipeline 922 or the media pipeline 924. In some embodiments, GPGPU operations are configured and executed in a similar manner as media operations. [01 19] Figure 14 illustrates exemplary graphics software architecture for a data processing system 1000 according to some embodiments. In some embodiments, software architecture includes a 3D graphics application 1010, an operating system 1020, and at least one processor 1030. In some embodiments, processor 1030 includes a graphics processor 1032 and one or more general-purpose processor core(s) 1034. The graphics application 1010 and operating system 1020 each execute in the system memory 1050 of the data processing system.

[0120] In some embodiments, 3D graphics application 1010 contains one or more shader programs including shader instructions 1012. The shader language instructions may be in a high-level shader language, such as the High Level Shader Language (HLSL) or the OpenGL Shader Language (GLSL). The application also includes executable instructions 1014 in a machine language suitable for execution by the general-purpose processor core 1034. The application also includes graphics objects 1016 defined by vertex data.

[0121 ] In some embodiments, operating system 1020 is a Microsoft® Windows® operating system from the Microsoft Corporation, a proprietary UNIX-like operating system, or an open source UNIX-like operating system using a variant of the Linux kernel. The operating system 1020 can support a graphics API 1022 such as the Direct3D API, the OpenGL API, or the Vulkan API. When the Direct3D API is in use, the operating system 1020 uses a front-end shader compiler 1024 to compile any shader instructions 1012 in HLSL into a lower-level shader language. The

compilation may be a just-in-time (JIT) compilation or the application can perform shader pre-compilation. In some embodiments, high-level shaders are compiled into low-level shaders during the compilation of the 3D graphics application 1010. In some embodiments, the shader instructions 1012 are provided in an intermediate form, such as a version of the Standard Portable Intermediate Representation (SPIR) used by the Vulkan API.

[0122] In some embodiments, user mode graphics driver 1026 contains a back-end shader compiler 1027 to convert the shader instructions 1012 into a hardware specific representation. When the OpenGL API is in use, shader instructions 1012 in the GLSL high-level language are passed to a user mode graphics driver 1026 for compilation. In some embodiments, user mode graphics driver 1026 uses operating system kernel mode functions 1028 to communicate with a kernel mode graphics driver 1029. In some embodiments, kernel mode graphics driver 1029

communicates with graphics processor 1032 to dispatch commands and instructions.

[0123] One or more aspects of at least one embodiment may be implemented by representative code stored on a machine-readable medium which represents and/or defines logic within an integrated circuit such as a processor. For example, the machine-readable medium may include instructions which represent various logic within the processor. When read by a machine, the instructions may cause the machine to fabricate the logic to perform the techniques described herein. Such representations, known as "IP cores," are reusable units of logic for an integrated circuit that may be stored on a tangible, machine-readable medium as a hardware model that describes the structure of the integrated circuit. The hardware model may be supplied to various customers or manufacturing facilities, which load the hardware model on fabrication machines that manufacture the integrated circuit. The integrated circuit may be fabricated such that the circuit performs operations described in association with any of the embodiments described herein.

[0124] Figure 15 is a block diagram illustrating an IP core development system 1 100 that may be used to manufacture an integrated circuit to perform operations according to an embodiment. The IP core development system 1 100 may be used to generate modular, re-usable designs that can be incorporated into a larger design or used to construct an entire integrated circuit (e.g., an SOC integrated circuit). A design facility 1 130 can generate a software simulation 1 1 10 of an IP core design in a high level programming language (e.g., C/C++). The software simulation 1 1 10 can be used to design, test, and verify the behavior of the IP core using a simulation model 1 1 12. The simulation model 1 1 12 may include functional, behavioral, and/or timing simulations. A register transfer level (RTL) design 1 1 15 can then be created or synthesized from the simulation model 1 1 12. The RTL design 1 1 15 is an abstraction of the behavior of the integrated circuit that models the flow of digital signals between hardware registers, including the associated logic performed using the modeled digital signals. In addition to an RTL design 1 1 15, lower-level designs at the logic level or transistor level may also be created, designed, or synthesized. Thus, the particular details of the initial design and simulation may vary.

[0125] The RTL design 1 1 15 or equivalent may be further synthesized by the design facility into a hardware model 1 120, which may be in a hardware description language (HDL), or some other representation of physical design data. The HDL may be further simulated or tested to verify the IP core design. The IP core design can be stored for delivery to a 3 ^rd party fabrication facility 1 165 using non-volatile memory 1 140 (e.g., hard disk, flash memory, or any non-volatile storage medium). Alternatively, the IP core design may be transmitted (e.g., via the Internet) over a wired connection 1 150 or wireless connection 1 160. The fabrication facility 1 165 may then fabricate an integrated circuit that is based at least in part on the IP core design. The fabricated integrated circuit can be configured to perform operations in accordance with at least one embodiment described herein.

[0126] Figures 16-18 illustrated exemplary integrated circuits and associated graphics processors that may be fabricated using one or more IP cores, according to various embodiments described herein. In addition to what is illustrated, other logic and circuits may be included, including additional graphics processors/cores, peripheral interface controllers, or general purpose processor cores.

[0127] Figure 16 is a block diagram illustrating an exemplary system on a chip integrated circuit 1200 that may be fabricated using one or more IP cores, according to an embodiment. Exemplary integrated circuit 1200 includes one or more application processor(s) 1205 (e.g., CPUs), at least one graphics processor 1210, and may additionally include an image processor 1215 and/or a video processor 1220, any of which may be a modular IP core from the same or multiple different design facilities. Integrated circuit 1200 includes peripheral or bus logic including a USB controller 1225, UART controller 1230, an SPI/SDIO controller 1235, and an l ² S/l ² C controller 1240. Additionally, the integrated circuit can include a display device 1245 coupled to one or more of a high-definition multimedia interface (HDMI) controller 1250 and a mobile industry processor interface (MIPI) display interface 1255. Storage may be provided by a flash memory subsystem 1260 including flash memory and a flash memory controller. Memory interface may be provided via a memory controller 1265 for access to SDRAM or SRAM memory devices. Some integrated circuits additionally include an embedded security engine 1270.

[0128] Figure 17 is a block diagram illustrating an exemplary graphics processor 1310 of a system on a chip integrated circuit that may be fabricated using one or more IP cores, according to an embodiment. Graphics processor 1310 can be a variant of the graphics processor 1210 of Figure 16. Graphics processor 1310 includes a vertex processor 1305 and one or more fragment processor(s)

1315A1315N (e.g., 1315A, 1315B, 1315C, 1315D, through 1315N-1 , and 1315N). Graphics processor 1310 can execute different shader programs via separate logic, such that the vertex processor 1305 is optimized to execute operations for vertex shader programs, while the one or more fragment processor(s) 1315A-1315N execute fragment (e.g., pixel) shading operations for fragment or pixel shader programs. The vertex processor 1305 performs the vertex processing stage of the 3D graphics pipeline and generates primitives and vertex data. The fragment processor(s) 1315A-1315N use the primitive and vertex data generated by the vertex processor 1305 to produce a framebuffer that is displayed on a display device. In one embodiment, the fragment processor(s) 1315A-1315N are optimized to execute fragment shader programs as provided for in the OpenGL API, which may be used to perform similar operations as a pixel shader program as provided for in the Direct 3D API.

[0129] Graphics processor 1310 additionally includes one or more memory management units (MMUs) 1320A-1320B, cache(s) 1325A-1325B, and circuit interconnect(s) 1330A-1330B. The one or more MMU(s) 1320A-1320B provide for virtual to physical address mapping for integrated circuit 1310, including for the vertex processor 1305 and/or fragment processor(s) 1315A-1315N, which may reference vertex or image/texture data stored in memory, in addition to vertex or image/texture data stored in the one or more cache(s) 1325A-1325B. In one embodiment the one or more MMU(s) 1325A-1325B may be synchronized with other MMUs within the system, including one or more MMUs associated with the one or more application processor(s) 1205, image processor 1215, and/or video processor 1220 of Figure 17, such that each processor 1205-1220 can participate in a shared or unified virtual memory system. The one or more circuit interconnect(s) 1330A- 1330B enable graphics processor 1310 to interface with other IP cores within the SoC, either via an internal bus of the SoC or via a direct connection, according to embodiments.

[0130] Figure 18 is a block diagram illustrating an additional exemplary graphics processor 1410 of a system on a chip integrated circuit that may be fabricated using one or more IP cores, according to an embodiment. Graphics processor 1410 can be a variant of the graphics processor 1210 of Figure 16. Graphics processor 1410 includes the one or more MMU(s) 1320A-1320B, caches 1325A-1325B, and circuit interconnects 1330A-1330B of the integrated circuit 1300 of Figure 17.

[0131] Graphics processor 1410 includes one or more shader core(s) 1415A- 1415N (e.g., 1415A, 1415B, 1415C, 1415D, 1415E, 1415F, through 1315N-1 , and 1315N), which provides for a unified shader core architecture in which a single core or type or core can execute all types of programmable shader code, including shader program code to implement vertex shaders, fragment shaders, and/or compute shaders. The exact number of shader cores present can vary among embodiments and implementations. Additionally, graphics processor 1410 includes an inter-core task manager 1405, which acts as a thread dispatcher to dispatch execution threads to one or more shader cores 1415A-1415N and a tiling unit 1418 to accelerate tiling operations for tile-based rendering, in which rendering operations for a scene are subdivided in image space, for example to exploit local spatial coherence within a scene or to optimize use of internal caches.

[0132] The following clauses and. /or examples pertain to further embodiments:

One example embodiment may be a method comprising reusing, in a child node, a computation for a parent node in a reduced precision bounding volume hierarchy ray traversal for graphics processing. The method may also include for minimum node coordinates, identifying coordinates that are different from the minimum parent node coordinates. The method may include calculating differences between parent and child node coordinates. The method may include quantizing the differences. The method may include for maximum node coordinates, identifying coordinates that are different from the maximum parent node coordinates. The method may include calculating differences between parent and child node coordinates. The method may include quantizing the differences. The method may include determining where a ray enters a bounding box and using a first quantized coordinate to get a first parametric distance The method may include

determining where the rays exists in the bounding box using a second quantized coordinate to get a second parametric distance The method may include

comparing to determine ray/bounding box intersection by multiplying the

ray's slope and and the ray's slope and using reduced precision multiplication.

[0133] Another example embodiment may be at least one non-transitory computer readable media storing instructions to perform a sequence comprising reusing, in a child node, a computation for a parent node in a reduced precision bounding volume hierarchy ray traversal for graphics processing. The media may include for minimum node coordinates, identifying coordinates that are different from the minimum parent node coordinates. The media may include calculating differences between parent and child node coordinates. The media may include quantizing the differences. The media may include for maximum node coordinates, identifying coordinates that are different from the maximum parent node coordinates. The media may include calculating differences between parent and child node coordinates. The media may include quantizing the differences. The media may include determining where a ray enters a bounding box and using a first quantized coordinate to get a first parametric distance The media may include determining where the rays exists in the bounding box using a second quantized coordinate to get a second parametric distance The media may include comparing μ _i and to determine ray/bounding

box intersection by multiplying the ray's slope and and the ray's slope and using reduced precision multiplication.

[0134] In another example embodiment may be an apparatus comprising a processor to reuse, in a child node, a computation for a parent node in a reduced precision bounding volume hierarchy ray traversal for graphics processing, and a memory coupled to said processor. The apparatus of said processor to include for minimum node coordinates, identify coordinates that are different from the minimum parent node coordinates. The apparatus of said processor to calculate differences between parent and child node coordinates. The apparatus of said processor to quantize the differences. The apparatus of said processor to include for maximum node coordinates, identify coordinates that are different from the maximum parent node coordinates. The apparatus of said processor to calculate differences between parent and child node coordinates. The apparatus of said processor to quantize the differences. The apparatus of said processor to determine where a ray enters a bounding box and using a first quantized coordinate r _t to get a first parametric distance X _t . The apparatus of said processor to determine where the rays exists in the bounding box using a second quantized coordinate s _i to get a second parametric distance μ _i . The apparatus of said processor to compare μ _i and X _t to determine ray/bounding box intersection by multiplying the ray's slope and X _t and the ray's slope and μ _ί using reduced precision multiplication.

[0135] The graphics processing techniques described herein may be implemented in various hardware architectures. For example, graphics functionality may be integrated within a chipset. Alternatively, a discrete graphics processor may be used. As still another embodiment, the graphics functions may be implemented by a general purpose processor, including a multicore processor.

[0136] References throughout this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation

encompassed within the present disclosure. Thus, appearances of the phrase "one embodiment" or "in an embodiment" are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be instituted in other suitable forms other than the particular embodiment illustrated and all such forms may be encompassed within the claims of the present application.

[0137] While a limited number of embodiments have been described, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this disclosure.