2. Background [0002] Conventional computer systems typically include several functional components. These components may include a central processing unit (CPU), main memory, input/output ("I/O") devices, and disk drives. In conventional systems, the main memory is coupled to the

CPU via a system bus or a local memory bus. The main memory is used to provide the CPU access to data and/or program information that is stored in main memory at execution time. Typically, the main memory is composed of random access memory (RAM) circuits. A computer system with the CPU and main memory is often referred to as a host system.

(00031 The main memory is typically smaller than disk drives and may be volatile. Programming data is often stored on the disk drive and read into main memory as needed. The disk drives are coupled to the host system via a disk controller that handles complex details of interfacing the disk drives to the host system.

Communications between the host system and the disk controller is usually provided using one of a variety of standard I/O bus interfaces.

[0004] Typically, a disk drive includes one or more magnetic disks. Each disk typically has a number of concentric rings or tracks on which data is stored. The tracks themselves may be divided into sectors, which are the smallest accessible data units. A positioning head above the appropriate track accesses a sector. An index pulse typically identifies the first sector of a track.

The start of each sector is identified with a sector pulse.

[0005] Typically, the disk drive waits until a desired sector rotates beneath the head before proceeding for a read or write operation. Data is accessed serially, one bit at a time and typically, each disk has its own read/write head.

[0006] The disk drive is connected to the disk controller that performs numerous functions, for example, converting digital data to analog head signals, disk formatting, error checking and fixing, logical to physical address mapping and data buffering. To perform the various functions for transferring data, the disk controller includes numerous components.

[0007] Typically, the data buffering function is used to transfer data between the host and the disk. Data buffering is needed because the speed at which the disk drive can supply data or accept data from the host is different than the speed at which the host can correspondingly read or supply data. Conventional systems include a buffer memory that is coupled to the disk controller. The buffer memory temporarily stores data that is being read from or written to the disk drive.

[0008] Conventionally, when data is read from the disk drive, a host system sends a read command to the disk controller, which stores the read command into the buffer memory. Data is read from the disk drive and stored in the buffer memory. An ECC module determines the errors

that occur in the data and appropriately corrects those errors in the buffer memory. Once it is determined that there are no errors, data is transferred from the buffer memory to the host system.

[0009] Conventional disk controllers do not have an embedded processor or specific modules that can efficiently perform the complex functions expected from disk controllers.

[0010] Conventional disk controllers cannot access plural external memory having different timing characteristics.

In addition, conventional controllers do not easily permit use of different bus data width to which external memory is coupled. In addition, conventional disk controllers do not have a built in module that can track bus activity and hence provide valuable information for de-bugging. In conventional disk controllers, the disk controller must be coupled to an external bus analyzer to debug and/or monitor bus activity. This process is cumbersome and requires additional pins on the disk controller. In addition, conventional monitoring techniques cannot easily isolate components within the disk controller that need to be monitored. Furthermore, conventional disk controllers do not have a dedicated module that controls, prioritizes and generates interrupts.

[0011] Therefore, what is desired is an embedded disk controller system that can efficiently function in the fast paced, media storage environment.

SUMMARY OF THE INVENTION [0012] The present invention solves the foregoing drawbacks by providing an embedded controller with more than one processor. In one aspect of the present invention, a system for an embedded disk controller is provided. The system includes, a first main (system control) processor operationally coupled to a high performance bus; a second processor operationally coupled to a peripheral bus; a bridge that interfaces between the high performance and peripheral bus; and an external bus controller coupled to the high performance bus and operationally coupled to external devices via an external bus interface.

[0013] The system also includes an interrupt controller module that can generate a fast interrupt and prioritize interrupt requests to the first main processor.

[0014] Also provided is a history module coupled to the high performance and peripheral bus for monitoring bus activity; and a servo controller that is coupled to the second processor through a servo controller interface and provides real time servo controller information to the second processor. The second processor may be a digital

signal processor that is operationally coupled to the first main processor through an interface.

[0015] In another aspect of the present invention, the system may be an application specific integrated circuit ("ASIC"). In one aspect of the present invention, because the system has dual embedded processors with dedicated history module, interrupt controller module, servo controller and external bus controller, it can perform various functions independently and in parallel. This also improves communication between a host and external device.

[0016] In another aspect, dual processors also provide a real time overlap for processing host commands. For example, one processor may move the actuator while the other processor translates the LBA into physical information and queue host requests. The dual processors also improve overall performance for the host. It also allows data recovery when ECC cannot correct data failures. Using unique data recovery algorithms and error recovery information data may be recovered where ECC module fails to dynamically correct the data.

[0017] In one aspect of the present invention, a system for an embedded disk controller is provided.

The system includes a first main processor operationally coupled to a high performance bus and a second processor operationally coupled to a

peripheral bus. The system further includes an external bus interface controller ("EBC") for managing devices external to the system via an external bus interface, wherein the EBC is coupled to the high performance bus and includes at least a segment descriptor register and at least a device range register. The segment descriptor register allows firmware to program timing characteristics of the devices. The device range register enables the first main processor to access an address space in the devices.

[0018] In another aspect of the present invention, a method for controlling devices external to an embedded disk controller with a first main processor operationally coupled to a high performance bus and a second processor operationally coupled to a peripheral bus is provided. The method includes receiving an input signal; determining the external device's timing characteristics and device range that is a target for a read or write cycle; and asserting a write enable or read enable signal based on the input signal.

[0019] In yet another aspect of the present invention, the system with an external bus interface controller ("EBC") for managing devices external to an embedded disk controller is provided. The system

includes a state machine logic with a first idle state until a valid input signal is received; a first decoding stage for decoding an address to determine which external device is a target for a read or write cycle ; a second decoding stage that avoids data extension on an external bus; and a chip select signal stage during which an output signal is generated.

[0020] In one aspect of the present invention, the main processor in an embedded disk controller can access multiple devices with different timing characteristics or data width.

[0021] In yet another aspect of the present invention, a history module for monitoring plural components in an embedded disk controller with a first main processor operationally coupled to a first bus and a second processor operationally coupled to a second bus is provided. The history module includes an event control module that receives break point conditions that stops the history module from recording information of a component; and a first register that allows selection or-de-selection of certain components in the embedded disk controller.

The first register can also store a trigger mode value, which specifies a number of entries that are

made in history module buffer (s) after a break point condition is detected.

[00221 The history module continues to record information until a break point condition is encountered. The history module may stop or continue to test for break point condition even after a break point condition is encountered. An interrupt module generates an interrupt after a break point condition is detected and an interrupt source is enabled.

[0023] The history module also uses a second register that includes a pointer which tracks where a next entry in a history module buffer will be made while the history module is recording information.

[0024] In another aspect of the present invention, a method for monitoring plural components in an embedded disk controller with a first main processor operationally coupled to a first bus and a second processor operationally coupled to a second bus is provided. The method includes, determining if break point testing is enabled; determining if a trigger mode field is set up; and testing for break point condition if a break point condition is set.

[0025] In one aspect of the present invention, the history module selects specific slave or peripheral transactions for recording based on a slave or

peripheral mask. This allows selective monitoring of components.

[0026] In yet another aspect of the present invention, the process provides break point conditions for stopping History module recording.

However, external break point signal may be continually provided after recording stops. In addition, break point conditions may be provided for an Address/Data break point and an Address Range break point. In another aspect of the present invention, an external analyzer is not required to record bus transactions. This saves pins and the effort required for connecting an embedded disk controller to an external device so that its components can be monitored.

[0027] In one aspect of the present invention, a method for generating interrupts in an embedded disk controller is provided. The method includes receiving vector values for an interrupt; determining if an interrupt request is pending; comparing the received vector value with a vector value of the pending interrupt; and replacing a previous vector value with the received vector value if the received vector value has higher priority.

[0028] In another aspect of the present invention, a method for generating a fast interrupt in an embedded

disk controller is provided. The method includes, receiving an input signal from a fast interrupt source; and generating a fast interrupt signal based on priority and a mask signal.

[0029] In another aspect of the present invention, a system for generating interrupts in an embedded disk controller is provided. The system includes, at least one register for storing a trigger mode value which specifies whether an interrupt is edge triggered or level sensitive, and a vector address field that specifies a priority and address for an interrupt, and a mask value which masks an interrupt source.

[0030] In yet another aspect of the present invention, a system for generating fast interrupts in an embedded disk controller is provided. The system includes at least one register for storing a trigger mode value, which specifies whether an interrupt is edge triggered or level sensitive, and a mask value which masks, a fast interrupt source.

[0031] In one aspect of the present invention, a fast interrupt scheme is provided so that for critical interrupts, the main processor does not have to wait.

[0032] In another aspect of the present invention, interrupt priority is established efficiently by a scanning process. In yet another aspect of the present

invention, firmware can change priority and mask interrupts from any source, providing flexibility to a user.

[0033] This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiments thereof in connection with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS [0034] The foregoing features and other features of the present invention will now be described. In the drawings, the same components have the same reference numerals. The illustrated embodiment is intended to illustrate, but not to limit the invention. The drawings include the following Figures: [0035] Figure 1 is a block diagram of a hard disk controller in the prior art; [0036] Figures 2A-2B (referred herein as Figure 2) is a block diagram of an embedded disk controller, according to one aspect of the present invention; [0037] Figure 3 is a block diagram of an external bus controller, according to one aspect of the present invention; [0038] Figures 4A, 4B and 4C (referred herein as Figure 4) show a table with various input signals to the

external bus controller, according to one aspect of the present invention; [0039] Figures 5A-5C (referred herein as Figure 5) show a table with various output signals from the external bus controller, according to one aspect of the present invention; [0040] Figure 6 is a table showing a register map used by the external bus controller, according to one aspect of the present invention; [0041] Figures 7-9 show various registers with plural fields that are used by the external bus controller, according to one aspect of the present invention; [0042] Figures 10-13 show various timing diagrams for the external bus controller, according to one aspect of the present invention; [0043] Figure 14 is a functional block diagram of the external bus controller, according to one aspect of the present invention; [0044] Figure 15 is a state machine diagram of the external bus controller, according to one aspect of the present invention; [0045] Figure 16 is a block diagram of an interrupt controller, according to one aspect of the present invention; [0046] Figures 17A-17B (referred herein as Figure 17) show a table with various input signals to the interrupt

controller, according to one aspect of the present invention; [00473 Figure 18 is a table showing various output signals from the interrupt controller, according to one aspect of the present invention ; [0048] Figure 19 is a table showing a register map used by the interrupt controller, according to one aspect of the present invention; [0049] Figures 20-26 show various registers with various fields that are used by the interrupt controller, according to one aspect of the present invention; [0050] Figures 27A-27B (referred herein as Figure 27) show a functional block diagram of the interrupt controller, according to one aspect of the present invention ; [0051] Figure 28 is a process flow diagram for generating interrupts, according to one aspect of the present invention; [0052] Figure 29 is a process flow diagram for setting interrupt priority, according to one aspect of the present invention; [0053] Figure 30 is a state machine diagram used by the interrupt controller, according to one aspect of the present invention; [0054] Figure 31 is a block diagram of history module, according to one aspect of the present invention;

[0055] Figures 32A-1 to 32A4-4 show a table with various input signals to the history module, according to one ) aspect of the present invention ; [0056] Figure 32B is a table showing various output signals from the history module, according to one aspect of the present invention; [0057] Figures 33-43 show various registers with various fields that are used by the history module, according to one aspect of the present invention; [0058] Figures 44A-44B (referred to herein as Figure 44) show a functional block diagram of the history module, according to one aspect of the present invention; [0059] Figure 45 is a flow diagram of process steps for updating a history stack pointer, according to one aspect of the present invention; [0060] Figures 46-49 show various registers with various fields that are used as"mail boxes", according to one aspect of the present invention; [0061] Figure 50 shows a flow diagram of process steps for inter-processor communication, according to one aspect of the present invention; and [0062] Figures 51-53 show various registers with various fields that are used for indirect access of a memory module, according to one aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0063] To facilitate an understanding of the preferred embodiment, the general architecture and operation of a disk controller will be described initially. The specific architecture and operation of the preferred embodiment will then be described.

[0064] The disk drive system of Figure 1 is an example of an internal (hard) disk drive included in a computer system. The host computer (not shown) and the disk drive communicate via port 102, which is connected to a data bus (not shown). In an alternate embodiment (not shown), the disk drive is an external storage device, which is connected to the host computer via a data bus. The data bus, for example, is a bus in accordance with a Small Computer System Interface (SCSI) specification. Those skilled in the art will appreciate that other communication buses known in the art can be used to transfer data between the disk drive and the host system.

[0065] As shown in Figure 1, the disk drive includes disk controller 101, which is coupled to SCSI port 102, disk port 114, buffer memory 111 and microprocessor 100.

Interface 118 serves to couple microprocessor bus 107 to microprocessor 100. It is noteworthy that microprocessor 100 is not on the same chip as disk controller 101. A read only memory ("ROM") omitted from the drawing is used to store firmware code executed by microprocessor 100. Disk port 114 couples disk controller 101 to disk 115.

[0066] As is standard in the industry, data is stored on disk 115 in sectors. Each sector is byte structured and includes various fields, referred to as the sector format.

A typical sector format includes a logical block address ("LBA") of about four bytes followed by a data field of about 512 bytes. The LBA contains position information, for example, cylinder, head and sector numbers. A field for a CRC checksum of 4 bytes typically follows the data field. A subsequent field for a number of ECC bytes, for example 40-80 bytes, is located at the end of the sector.

[0067] Controller 101 can be an integrated circuit (IC) (or application specific integrated circuit"ASIC") that comprises of various functional modules, which provide for the writing and reading of data stored on disk 115.

Microprocessor 100 is coupled to controller 101 via interface 118 to facilitate transfer of data, address, timing and control information. Buffer memory 111 is coupled to controller 101 via ports to facilitate transfer of data, timing and address information.

[0068] Data flow controller 116 is connected to microprocessor bus 107 and to buffer controller 108. An ECC module 109 and disk formatter 112 are both connected to microprocessor bus 107. Disk formatter 112 is also coupled to data and control port 113 and to data bus 107.

[0069] SCSI controller 105 includes programmable registers and state machine sequencers that interface with

SCSI port 102 on one side and to a fast, buffered direct memory access (DMA) channel on the other side.

[0070] Sequencer 106 supports customized SCSI sequences, for example, by means of a 256-location instruction memory that allows users to customize command automation features. Sequencer 106 is organized in accordance with the Harvard architecture, which has separate instruction and data memories. Sequencer 106 includes, for example, a 32-byte register file, a multi-level deep stack, an integer algorithmic logic unit (ALU) and other special purpose modules. Sequencer 106 support's firmware and hardware interrupts schemes. The firmware interrupt allows microprocessor 100 to initiate an operation within Sequencer 106 without stopping sequencer operation.

Hardware interrupt comes directly from SCSI controller 105.

[0071] Disk formatter 112 is a disk interface controller and performs control operations when microprocessor 100 loads all required control information and parameter values into a writable control store (WCS) RAM (not shown) and issues a command. Disk formatter 112 executes the command with no microprocessor 100 intervention.

[0072] Buffer controller 108 can be a multi-channel, high speed DMA controller. Buffer controller 108 connects buffer memory 111 to disk formatter 112 and to an ECC channel of ECC module 109, a SCSI channel of SCSI

controller 105 and micro-controller bus 107. Buffer controller 108 regulates data movement into and out of buffer memory 111.

[00731 To read data from disk 115, a host system sends a read command to disk controller 101, which stores the read commands in buffer memory 111. Microprocessor 100 then read the command out of buffer memory 111 and initializes the various functional blocks of disk controller 101.

Data is read from disk 115 and is passed through disk formatter 112 simultaneously to buffer controller 108 and to ECC module 109. Thereafter, ECC module 109 provides the ECC mask for errors, which occurred during the read operation, while data is still in buffer controller 108.

The error is corrected and corrected data is sent to buffer memory 111, and then passed to the host system.

[0074] Figure 2 shows a block diagram of an embedded disk controller system 200 according to one aspect of the present invention that not only includes the functionality of disk controller 101, but also includes various other features to meet the demands of storage industry. System 200 may be an application specific integrated circuit ("ASIC").

[0075] System 200 includes a microprocessor ("MP") 240 (which is also the overall system processor) that performs various functions described below. MP 240 may be a Pentium @ Class processor designed and developed by Intel

Corporation @ or an ARM processor (for example, ARM966E-S or any other processor. MP 240 is operationally coupled to various system 200 components via buses 236 and 208.

Bus 236 may be an Advanced High performance (AHB) bus as specified by ARM Inc. Bus 208 may an Advanced Peripheral Bus ("APB") as specified by ARM Inc. The specifications for AHB and APB are incorporated herein by reference in their entirety. It is noteworthy that the present invention is not limited to any particular bus or bus standard.

[0076] Arbiter 245 arbitrates access to AHB bus 236, while APB bridge 235 is used to communicate between buses 236 and 208.

[0077] System 200 is also provided with a random access memory (RAM) or static RAM (SRAM) 238 that stores programs and instructions, which allows MP 240 to execute computer instructions. MP 240 may execute code instructions (also referred to as"firmware") out of RAM 238.

[0078] System 200 is also provided with read only memory (ROM) 237 that stores invariant instructions, including basic input/output instructions.

[0079] MP 240 includes a TAP controller 242 that performs various de-bugging functions.

[0080] MP 240 is also coupled to an External Bus Interface Bridge (or Controller) ("EBC"also referred to as"EBI"or"EBI controller") 228 via an external bus

interface ("EBI/F") 227. EBC 228 allows system 200 via MP 240 and EBI/F 227 to read and write data using an external bus, for example, a storage device external to system 200, including FLASH memory, read only memory and static RAM.

EBC 228 may be used to control external memory (not shown), as discussed in detail below. EBI/F 227 may be programmed to interface with plural external devices.

[0081] System 200 includes an interrupt controller ("IC") 207 that can generate regular interrupts (IRQ 207A) or a fast interrupt (FIQ 207B) to MP 240. In one aspect of the present invention, IC 207 is an embedded system that can generate interrupts and arbitrates between plural interrupts. IC 207 is described below in detail.

[0082] System 200 includes a serial interface ("UART") 201 that receives information via channel 203 and transmits information via channel 204.

[0083] System 200 includes registers 209 that include configuration, system control, clock and power management information.

[0084] System 200 also includes an address break point and history module (also referred to as"history module" or"history stack") 234 that monitors activity on busses 236 and 208 and builds a history stack. Such history stack may be used for debugging, and monitoring plural components of system 200. History module 234 is discussed below in detail.

[0085] System 200 also includes a timer module 206 that controlled by MP 240 and includes various timers, for example, the"Watchdog timer".

[0086] System 200 is provided with a general purpose input/output ("GPIO") module 202 that allows GPIO access to external modules (not shown).

[0087] System 200 is also provided with a digital signal processor ("DSP") 229 that controls and monitors various servo functions through DSP interface module ("DSPIM") 210 and servo controller interface 212 operationally coupled to a servo controller 216.

[0088] DSPIM 109 interfaces DSP 229 with MP 240 and updates a tightly coupled memory module (TCM) 212 (also referred to as"memory module"212) with servo related information. MP 240 can access TCM 212 via DSPIM 210.

[0089] Servo controller interface ("SCI") 211 includes an APB interface 214 that allows SCI 211 to interface with APB bus 208 and allows SC 216 to interface with MP 240 and DSP 229. SCI 211 also includes DSPAHB interface 215 that allows access to DSPAHB bus 233. SCI 211 is provided with a digital to analog/analog to digital converter 213 that converts data from analog to digital domain and vice- versa. Analog data 223 enters module 213 and leaves as data 222 to a servo drive 221.

[0090] SC 212 has a read channel device (RDC) interface 217, a spindle motor control ("SVC") interface 219, a head

integrated circuit (HDIC) interface 218 and servo data ("SVD") interface 219A.

[0091] System 200 also includes a hard disk controller 101A that is similar to the HDC 101 and includes a code cache 101B.

[0092] In one aspect of the present invention, because system 200 includes, dual embedded processors (MP 240 and DSP 229) with dedicated history module 234, IC module 207, servo controller and EBC 228, it can perform various functions independently. This not only saves the resources of MP 240 but also improves communication between a host and an external device.

[0093] In another aspect, embedded processors (MP 240 and DSP 229) provide independent real time control, with one processor as the system control processor (MP 240) and the second processor (DSP 229) as a slave to the first for real time control of the disk servo mechanism. DSP 229 as a slave also provides real time control for positioning a disk actuator. This includes analyzing error positioning data and outputting error correction data.

[0094] Dual processors also provide a real time overlap for processing host commands. For example, one processor may move the actuator while the other processor translates the LBA into physical information and queue host requests.

[0095] The dual processors also improve overall performance for the host. It also allows data recovery

when ECC cannot correct data failures. Using unique data recovery algorithms and error recovery information data may be recovered if the ECC module 109 fails to dynamically correct the data.

[0096] The following describes the various components of system 200 in detail, according to various aspects of the present invention.

[00973 EBC 228 [0098] EBC 228 is a slave on AHB bus 236 and adapts the high performance of AHB bus 236 to a slower external bus (not shown) that can support external memory (including without limitation, flash memory, ROM, and static memory (not shown) ). Figure 3 shows a block diagram of EBC 228 with various input signals (300-313) and output signals (314-323). Figure 4 provides a table describing signals 300-313 and Figure 5 provides a table describing signals 314-323.

[0099] In one aspect of the present invention, MP 240 via EBC 228 may access multiple devices with different timing characteristics or data width. At least a Segment Descriptor register is provided, which specifies the timing characteristic of each external device. Also provided is at least a device range register, which specifies the size of the external device address space.

Depending on the external bus data width, EBC 228 may

convert AHB bus 236 transactions into multiple external bus transactions.

[0100] Figure 6 provides a register map 600 for EBC 228, according to one aspect of the present invention.

Register map 600 includes segment descriptor registers 601, device range registers 602, and EBC 228 configuration register 603.

[01013 Each device segment descriptor register 601 may be formatted the same way with the same fields. Segment descriptor registers 601 allow firmware to program timing characteristics for an external memory device on an external memory bus. For example, as shown in the table of Figure 6, four segment descriptor registers 601 may include timing intervals for four different devices. It is noteworthy that the example in Figure 6 is only to illustrate the adaptive aspects of the present invention and not to limit the number of devices to just four. Any number of devices may be used.

[0102] Figure 7 provides a description of the segment register 601 values. MP 240 writes the values in segment registers 601 during initialization. Register (s) 601 includes various values (601A-601G) that allow the firmware to program timing characteristics for an external memory device. Values include a Write Hold Wait State (WHW) 601A, Transaction Recovery Wait States 601B, Setup 2 Wait States (SW2) 601C, Setup 1 Wait States (SW1) 601D,

Data Width (DW) 601E, Write Wait States (WW) 601F and Read Wait State (RW) 601G, as described in Figure 7.

[0103] DW 601E specifies the data width of an external bus device (not shown). A state machine may be used by EBC 228 to use the various register 601 values, as shown by the state machine diagram in Figure 15 and discussed below. It is noteworthy that the invention is not limited to the command terminology of Figure 7.

[0104] Figure 8 provides a description of device range registers 602. An enable ("EN") bit 602A is set to access the address range of a device, while the device range (DvRng) 602B specifies the number of blocks that may be addressed within the device address space. MP 240 to allow access to the address space within a particular device address initializes device range register 602.

[0105] Figure 9 shows the plural fields (603A and 603B) used for configuring EBC 228. Device allocation bit 603B specifies the number of devices allocated on the external bus (not shown) and field 603A is used to read the external bus width as supported by EBC 228.

[0106] Figure 14 shows a functional block diagram of system 1400 used in EBC 228 for supporting plural external devices. Input signals 302 and 307 from AHB bus 236 are sent to a validation module 1401 that validates the incoming signals. A valid signal is then sent to state machine logic 1402.

[0107] System 1400 includes a set of registers, for example, HaddrReg 1408, HwriteReg 1411 and HsizeReg 1412 register and their usage is described below.

[0108] Figure 15 shows a state machine diagram of process steps used by state machine logic 1402. The following provides a description of the plural states used by state machine logic 1402 to implement the adaptive aspects of the present invention.

[0109] State SO : This is an idle state, until a valid operation on the bus is received.

[0110] State S1 : This is a first stage for decoding an address in HaddreReg 1408 to determine which external device if any, is the target for a read or write cycle.

After determining the target external device, various counter values, as shown in Figure 15, are loaded during this state.

[0111] State S2: This is a second state during which state machine 1402 remains in this stage until the SW1 601D and TRW 601B values expire to avoid data contention on the external bus.

[0112] State S3: The state machine stays in this state for at least one clock cycle with all external bus controls as being inactive. This state is only used for sequential write operations.

[01133 State S4: During this state the appropriate chip select signal (XCS 317) is asserted while the write enable

(XWEn 319) or output enable (XOEn 318) are deasserted, until SW2 601C expires.

[0114] State S5: The state machine logic 1402 stays in this state until a current read or write operation is completed. During this state the chip select, write enable or out enable signals are asserted. For write commands, EBC 228 writes data and for read operation, EBC 228 reads data.

[0115] State S6: This state is entered only during write operations and is used to provide write data hold time.

During this state, EBC 228 continues to drive the write data on the external bus while it keeps the write enable signal de-asserted.

[0116] State S7: During this state, registers within EBC 228 are read or written.

[0117] The relationship between the various states is shown in Figure 15.

[0118] Figures 10-13 show various timing diagrams using input signals 300-313 and output signals 314-323 with respect to the functional block diagram of system 1400 and the state diagram of Figure 15.

[0119] Figure 10 shows a diagram for a half word read access to a 16 bit external bus.

[0120] Figure 11 shows a diagram for a word read access to a 16 bit external bus.

[0121] Figure 12 shows a diagram for a half word write access to a 16 bit external bus.

[0122] Figure 13 shows a diagram for a word write access to a 16 bit external bus.

[0123] Interrupt Controller ("IC") 207: [01241 IC 207 synchronizes and prioritizes interrupt signals as a slave on the APB bus 208. IC 207 handles two types of interrupts, Fast Interrupt Request ("FIQ") and Interrupt Request ("IRQ"). The interrupts are sent to MP 240. The FIQ 207B is used for critical interrupts as defined by a user or firmware. IRQs 207A are provided for routine interrupts. IC 207 provides the interrupts to MP 240 that interrogates IC 207 to retrieve a particular interrupt with an interrupt vector, as described below.

MP 240 may clear the interrupt after retrieving the interrupt information.

[0125] In one aspect of the present invention, IC module 207, provides FIQ 207B for critical interrupts, scans interrupts for priority, prevents interrupt source lockout (interlock) in the interrupt service and allows a user to change various interrupt options using firmware.

[0126] Figure 16 shows IC 207 with various input signals (1601-1609) and output signals (1610-1614). Figure 17 and 18 provide a description of signals 1601-1609 and 1610- 1614, respectively.

[0127] IC module 207 uses plural registers for controlling interrupts. The base address of IC module 207 is specified in APB Bridge 235. When signal PSELIC 1604 from APB bridge 235 is sent to IC module 207, the base address of IC module 207 is detected by APB bridge 235 and IC module 207 decodes signals PADDR 1605 and PWRITE 1606 to select the appropriate register address. IC module 207 examines signal PADDR 1605 for exceptions. An access to an undefined or reserved register address results in IC module 207 asserting the PADREXCPT signal 1610 to APB Bridge 235. It is noteworthy that this does not change the state of IC module 207. Also, access to an undefined "read"address results in PADREXCPT signal 1610 to APB Bridge 235.

[0128] Figure 19 shows a register map 1900 for IC module 207. Register map 1900 includes a set of registers 1901 for IRQ control and a register 1904 for FIQ control.

Register 1902 stores a current FIQ interrupt and register 1903 is used to mask/unmask FIQ ability, via firmware.

[0129] Figure 20 shows details of register 1905 that provides status for an IRQ interrupt. Register 1905 includes field 1905A value for IRQValid. When the bit value for IRQValid is valid (for example, 1) then it indicates that IC module 207 has resolved an IRQ interrupt and the Vector Address field 1905B is valid.

[0130] Figure 21 shows details of register 1903 that allows firmware to mask the Interrupt ability. FIQ interrupt ability may be enabled or disabled by setting up FIQInt Mask field 1903B. In addition, by setting field 1903A, IRQ interrupt sources may be masked.

[01313 Figure 22 shows details of various fields used in register 1904, which is an interrupt control register for FIQ source. MK-Read only field 1904A is a copy of the mask bit from register 1903. Interrupt Request Sent ("IRS")-Read Only field 1904B is set when MP 240 reads the corresponding interrupt source as the prioritized interrupt from register 1902.

[0132] Interrupt Request Pending ("IRP") -Read Only field 1904C is set when a corresponding interrupt source is asserted. When IRS 1904B is set, IRP 1904C is cleared.

In addition, when the source interrupt is masked, IRP 1904C may be cleared. Polarity ("PLR") 1904D is used to specify the polarity of an interrupt source.

[0133] Register 1904 also includes a trigger mode TM value 1904E that specifies the mode of an interrupt source signal. Field 1904E specifies whether the interrupt signal is edge triggered or level sensitive. Use of TM 1904E in register 1904 is discussed below in detail.

[0134] Figure 23 provides various fields that are used in IRQ control register (s) 1901, which are interrupt control registers for IRQ sources. MK-Read only fields 1901A and

1901G are copies of the mask bits from register 1903.

Interrupt Request Sent ("IRS")-Read Only fields 1901B and 1901I are set when MP 240 reads the corresponding interrupt source as the prioritized interrupt from register 1905. Interrupt Request Pending ("IRP")-Read Only fields 1901C and 1901H are set when a corresponding interrupt source is asserted. When IRS 1901B or 1901I are set, IRP 1901C or 1901H are cleared respectively. In addition, when the source interrupt is masked, IRP 1901C and 1901H may be cleared. Polarity ("PLR") 1901D and 1901J are used to specify the polarity of the corresponding interrupt sources.

[0135] Register (s) 1901 also include trigger mode TM values 1901E and 1901K that specify the mode of the interrupt source signals. Field 1901E and 1901K specify whether the interrupt signal is edge triggered or level sensitive. Use of TM 1901E and 1901K in register (s) 1901 is discussed below in detail.

[0136] Fields 1901F and 1901L contain interrupt vector addresses assigned by MP 240 to a corresponding interrupt source. This field specifies a vector address to firmware and specifies the priority of the interrupt with the interrupt source. The vector field in 1905B is updated when an entry in the interrupt control register array (described below) that corresponds to an active interrupt

is seen as having a higher priority while the register array is being scanned.

[0137] Figure 24 shows the field used by register 1902.

Field 1902A, when valid indicates that there is a fast interrupt request asserted to MP 240. Field 1902A is cleared when register 1902 is read.

[01381 Figure 25 shows the fields used in register 1907.

Register 1907 is a control register showing when an interrupt has been sent. Field 1907A is used for a FIQ source and field 1907B is used for IRQ sources, as described below.

[0139] Figure 26 shows the fields for register 1906 used for pending interrupts. Field 1906A is used for an FIQ source and field 1906B is used for IRQ sources, as described below.

[0140] Figure 27 shows a functional block diagram of system 2000 used by IC module 207, in various adaptive aspects of the present invention.

[0141] FIQ Interrupts: [0142] Input signal 1608 from a FIQ source is sent to module 2005. Module 2005 selects either the FIQ source signal, or a TestSource signal depending on the state of ICIntTestControl 2017. If the FIQ source signal is selected, then it is synchronized by raw interrupt synchronization module 2006. The synchronized signal is

sent for FIQ registration to FIQ registration module 2007.

Module 2007 includes registers 1904, and 1902.

[0143] Signal 1607 is sent to mask module 2004 (that includes register 1903) and to FIQ IC module 2008. Mask module 2004 sends the mask (1903A) to FIQ IC module 2008, which then sends a signal to interrupt generation module 2009. Interrupt generation module 2009 also receives input from, IRQ Scanner 2011 and based upon the priority of the request, an interrupt is generated, for example FIQn 1611, SysInt 1614 and IRQn 1613.

[0144] When FIQIRP 1904C is set, then a fast interrupt is asserted. The interrupt request signal remains asserted until MP 240 reads register 1902. When register 1902 is read, FIQn signal 1611 is de-asserted by setting FIQIRS 1904B and clearing FIQIRP 1904C.

[0145] In one aspect, another interrupt request cannot be made until FIQIRS 1904B is cleared as follows : (a) If FIQ interrupt source as defined by TM 1904E is level sensitive then the firmware ensures that the FIQ interrupt source is de-asserted and then an end of interrupt ("EOI") is sent to IC 207 to clear the FIQIRS 1904B state; or (b) If the FIQ interrupt source as defined by TM 1904E is edge triggered, the firmware need only read register 1902, FIQIRP 1904C is cleared and FIQIRS 1904B is set. In edge triggered mode, FIQIRS clears when the interrupt

source de-asserts. The next interrupt does not occur until the interrupt source signal de-asserts, and asserts again.

[0146] IRQ Interrupts: [0147] Incoming IRQESOURCE signals 1609 is received by module 2002. Module 2002 selects either the IRQESOURCE signal, or TestSource signals depending on the state of ICTestControl 2015. If the IRQESOURCE signals are selected, then they are synchronized by raw interrupt synchronization module 2003. The synchronized signals are sent for IRQ registration to IRQ registration module 2013.

IRQ interrupt registration module 2013 sets the field 1906B in register 1906. Signal 1607 is sent to mask module 2004 (that includes register 1903) and to IRQ Interrupt Registration Module 2013. Mask module 2004 sends the mask (1903A) to IRQ Interrupt Registration module 2013, which then sends signals to the IRQ Priority Evaluation And Scanner module 2011 (also referred herein as"IRQ Scanner 2011"). It is noteworthy that firmware may mask an interrupt before it is sent to MP 240. This de-registers the interrupt by clearing field 1906B.

[0148] For each possible interrupt input, information regarding that interrupt is stored in IRQ register control array 1901. Register control array 1901 includes vector values (1901F and 1901L), TM values (1901E and 1901K) and PLR values (1901D and 1901J) for each interrupt source, i. e. even and odd source. MP 240 may write the foregoing

values in register control array 1901. Vector values 1901F and 1901L provide the offset for firmware to access the interrupt handler (Not shown) and establish the priority of the interrupt within plural interrupt sources, for example, 16 IRQ sources. It is noteworthy that the invention is not limited to 16 IRQ sources. In one aspect, the highest vector value is given the highest priority.

When one of the registers in register control array 1901 is read then, the mask, IRS, IRP, Vector, TM and PLR values are also read at the same time. Output 2012 from register control array 1901 is sent to IRQ scanner 2011 that scans the vector values, as described below. IRQ scanner 2011 provides an input 2011A to interrupt generator 2009 that generates IRQn 1613.

[0149] When MP 240 retrieves the IRQ interrupt from IC module 207 it reads register 1905 which sets the IRQIRS bit (1901B or 19011) associated with the interrupt source in register 1905, which prevents the same interrupt source from generating another interrupt until the IRQIRS bit is cleared.

[0150] In one aspect, another interrupt from the same source cannot be made until IRQIRS (1901B or 19011) is cleared as follows: (a) If the IRQ interrupt source is defined by TM 1901E or 1901K as level sensitive then the firmware ensures that the IRQ interrupt source is de-asserted. Thereafter, an

end of interrupt ("EOI") is sent to IC 207 to clear the IRQIRS 1901B or 19011 state; or (b) If the IRQ interrupt source is defined by TM 1901E or 1901K as edge triggered, the firmware need only read register 1905. IRQIRP 1901C or 1901H is cleared and IRQIRS 1901B or 19011 is set. In edge triggered mode, IRQIRS clears when the interrupt source de-asserts. The next interrupt does not occur until the interrupt source signal de-asserts, and asserts again.

[0151] Figure 28 is a flow diagram for IRQ generation with respect to the functional diagram of Figure 27 and the various registers described above.

[0152] In step S2800, an IRQ signal 1609 is received from an interrupt source.

[0153] In step S2801, IRQ signal 1609 is selected by logic 2002.

[0154] In step S2802, valid IRQ signal 1609A is synchronized by synchronization module 2003.

[0155] In step S2803, synchronized IRQ signal 1609B is registered by IRQ interrupt registration module 2013.

[0156] In step S2804, registers in register control array 1901 are read.

[0157] In step S2805, vector values are scanned (discussed below with respect to Figure 29).

[0158] In step S2806, based on the vector values, output interrupt signal 1613 is sent to MP 240.

[0159] Figure 29 is a flow diagram showing executable process steps used by IRQ scanner 2011.

[0160] In step S2900, IRQ scanner 2011 receives register values 2012 from register control array 1901 and IRQESOURCE 2013A from IRQ interrupt registration module 2013. IRQ scanner 2011 receives vector values from register control array 1901. IRQ scanner 2011 examines each interrupt during every interrupt cycle [0161] In step S2901, the process determines if an interrupt is being sent (sent as used here includes "pending"interrupts). If an interrupt is being sent (or pending), then in step S2902, IRQ scanner 2011 compares the vector values of the interrupt being sent (or pending) with the scanned vector values of every other active interrupt input in a given interrupt cycle.

[0162] In step S2903, IRQ scanner 2011 replaces the previous vector values if the most current vector values have higher priority.

[0163] If an interrupt is not being sent (or pending) in step S2901, then in step S2904, IRQ scanner 2011 loads the current vector values from an active interrupt input from S2901 and the process moves to step S2902.

[0164] Figure 30 shows a state diagram for interrupt control, according to one aspect of the present invention.

It is noteworthy, that although the state diagram of Figure 30 shows that it is for IRQ interrupts, the same

will also apply for FIQ interrupts. State diagram includes three states 3000,3001 and 3002. State 3000 is for receiving an interrupt request. State 3001 is an interrupt pending state and state 3002 is an interrupt sent state. Based on the foregoing discussions regarding Figures 16-29, the state transitions of state diagram in Figure 30 are self-explanatory.

[0165] In one aspect of the present invention, a fast interrupt scheme is provided so that for critical interrupts, MP 240 does not have to wait.

[0166] In another aspect of the present invention, interrupt priority is established efficiently by a scanning process.

[0167] In yet another aspect of the present invention, firmware can change priority and mask interrupts from any source, providing flexibility to a user and also optimizes MP 240 usage.

[0168] In another aspect of the present invention, use of TM values prevents interlocking of interrupt service by MP 240.

[0169] History Module 234: [0170] History module 234 is a peripheral on APB Bus 208 that records transaction information over either AHB Bus 236 and/or APB Bus 208. The recorded information may be used for debugging and analyzing firmware and hardware problems. History module 234 is set up and initiated

through APB Bridge 235 and information from History module 234 is extracted through APB Bridge 235. History module 234 includes a buffer (s) (not shown) for reading and writing recorded information.

[0171] Figure 31 shows a top-level block diagram of History Module 234 with plural input and output signals.

[0172] Figures 32A-1,32A-2, 32A-3,32A-4 and 32B provide a description of the input and output signals, respectively.

[0173] Figure 33 provides a listing of a register map 3309 used by History Module 234. Register map 3309 includes various registers that are used for setting up History Module 234 recording and control conditions. The base address of History Module 234 is specified in APB bridge 235 and when PSELABPHS 3108 is asserted to History Module 234, the base address has been detected by APB bridge 235. History Module 234 decodes PADDR 1605 and PWRITE 1606 to select accessed memory mapped registers.

[0174] Figure 34 provides a table for register 3300 with the various fields (3300A-3300J) to control and set up History Module 234. SelectMask 3300A field if set isolates certain components in system for monitoring and recording by History Module 234. Firmware can also filter read and/or write operations. By setting fields 3300B and 3300C, read and/or write operations are not recorded by History Module 234.

[0175] Field 3300J defines break point conditions for History Module 234. Break point conditions are those, which stop recording/monitoring by History Module 234.

Field 3300I enables break points, while break point testing stops after a break point is detected, if field 3300E is set.

[0176] Trigger mode field 3300G specifies the number of entries made in a History Module 234 buffer after a break point condition is detected.

[0177] Figure 35 shows register 3500 that stores a history stack pointer (referred to as"HstryStkPtr"or "HSP") 3501. HSP 3501 provides the address of the next entry at a given time, for either reading from, or writing to, the history module 234 buffer.

[0178] HSP 3501 may be zero at the beginning of a recording session. Firmware has the flexibility to change HSP 3501 values. In one aspect, firmware may set this value to zero. HSP 3501 allows the firmware to recover a recording regardless of the reason why a recording session stopped. HSP 3501 is incremented each time an entry is accessed from the history stack buffer.

[0179] Figure 36A shows register 3603 that provides the address break point pattern for address break point testing. Field 3602 provides the address break point pattern for such break point testing.

[0180] Figure 36B shows a data/address break point pattern register 3600 (DataAdrBPPReg 3600) that stores break point data pattern ("BPData") field 3601. BPDATA field 3601 is compared against a data and address break point condition. Based on the selected break point condition and the comparison a break point sets and recording by History Module 234 stops when the trigger mode is satisfied.

[0181] Figure 37 shows register 3700 that includes recorded AHB bus 236 information in history module 234 buffer. When register 3700 is read, history stack pointer 3501 is incremented.

[0182] Figure 38 shows register 3800 that includes recorded APB bus 208 address information (similar to register 3700). Register 3500 is incremented after register 3800 is read.

[0183] Figure 39 shows a control history register 3900 that includes recorded AHB bus 236 information. Register 3500 is incremented after register 3900 is read.

[0184] Figure 40 shows a control history register 4000 that includes recorded APB bus 208 information. Register 3500 is incremented after register 4000 is read.

[0185] Figure 41 shows register 4100, which includes AHB bus 236 or APB bus 208 data specified by the pointer value in register 3500. Register 3500 is incremented after register 4100 is read.

[0186] Figure 42 shows register 4200 that includes a Clear History Stack Buffer ("CHSB") field 4201.

Setting CHSB field 4201 clears HSP 3501. CHSB 4201 is set while zero data is being written to buffers 4313 to 4315.

[0187] Figure 43 shows register 4300 that includes a"Set EnableRecord"field 4300A that may be set by firmware.

When field 4300A is set, History module 234 starts recording and the recording stops when field 4300A is cleared.

[0188] Figure 44 is a functional block diagram, of history module 234 that will be described below with respective to various inventive aspects of the present inventions. History module 234 may be setup by firmware to perform its various function. Control information is written to register 3300. If a break point is desired for address and/or data, or address range, then MP 240 sets registers 3600 and 3603.

[0189] To start history module 234, field 4300A of register 4300 is set, that allows recording when signals HREADY 307 or PENABLE 1607 are asserted. In one aspect of the present invention, history module234 may record data simultaneously for buses 236 and 208. This allows history module 234 to write in buffers 4313,4314 and 4315.

Although Figure 44 shows three buffers for address, control and data information, the invention is not limited

to the number of buffers used by history module 234. For example, only one or more buffers may be used to implement the adaptive aspects of the present invention.

[01903 History module 234 continues to make entries until a break point (or event) is reached as defined by fields 33001 and 3330J in register 3300 or field 4300A is cleared by firmware, as discussed below in detail.

[0191] Valid Recorded Entry: Before recording, buffers 4313,4314 and 4315 are cleared by firmware issuing a "clear History stack Buffer Access 4201 command. All valid entries in buffer 4314 are cleared. When recording, field 4201 is toggled each time an entry is made in buffers 4313-4315.

[0192] Break Point and Break Point Interrupt: Firmware can set field 33001 to enable a break point defined by break point condition field 3300J. Event control module 4336 generates field 4300A value that is sent to flip-flop module 4323. Firmware can set field 4300A value that enables flip-flop module 4323. History module 234 tests for break point condition 3300J in every clock cycle as defined by firmware.

[0193] When history module 234 detects the defined break point condition then it stops recording bus transactions based on TM value 3300G and an interrupt may be generated, as discussed below. After a break point is detected, history module 234 stops recording and based on field

3300E setting either continues to test for the break condition or stops testing for the break point condition.

[0194] An interrupt is generated based on the detection of the break point condition and if field 3300F is set, after the interrupt source is enabled in IC module 207.

[01951 Break points may be set for address and/or data or address range based on fields 3601 and 3602. Firmware may also send a"Clear Enable Record status"field 4300A to trigger a firmware break point, if a firmware break point condition is set in 3300J.

[0196] Clock Slam: When a break point condition is detected, and if field 3300D is enabled (Enable clock Slam), history module 234 asserts signal ClkSlam 4343 to clock control via flip-flop module 4340. Break point condition 3300J', which indicates that a break point condition has occurred, is sent to event control module 4336 with trigger mode value 3300G. This stops all the clocks in system 200. This signal remains asserted until system 200 is reset. This allows system 200 component information to be scanned out for analysis and diagnosis using standard debugging tools.

[0197] Filter Control: History module 234 can selectively filter out system 200 components based on filter control command 4324. Filter control command 4324 is based on select mask field 3300A in register 3300. If field 3300A is set then transactions related to, a specific

peripheral (s) or slave (depending on the bus) is not recorded.

[0198] Trigger Mode: [0199] Trigger mode field 3300G specifies the number of entries that are made in buffers 4313-4315 after a break point condition has been detected. In one aspect, field 3300G may be set so that history module 207 stops recording within a single clock cycle, or may continue to record a pre-defined amount of data before stopping.

[0200] Starting and Stopping Recording : [0201] History module 234 starts and stops recording based on register 4300 fields. Field 4300A when set to "EnableRcrdReg", allows history module 234 to record.

Setting"Clear Enable Record and Status"bit in field 4300A stops history module 234 from recording and break point testing, unless specified otherwise by firmware.

[0202] Bus (208 and 236) transactions are recorded when EnableRcrdReg is set. Mux 4324 samples signals HREADY 307 and PENABLE 1603. The signals indicate that a valid transaction is on the bus that may be recorded unless masked by field 3300A.

[0203] History Stack Pointer: [0204] History stack pointer 3500, as shown in Figure 35, keeps track of where the next entry in buffer 4313-4315 will be made while history module 234 is recording. When an entry is made in buffers 4313-4315, pointer 3501 is

updated. When history module 234 stops making entries in buffers 4313-4315, the value of 3501 points to the last entry plus one.

[0205] Extracting Recorded History Information: [0206] As stated above, when recording stops, history stack pointer 3501 points to the"oldest recorded entry".

MP 240 bus master (not shown) reads the history address buffer 4313 and history module 234 places the recorded entry into register 4300 (Figure 43) and history stack pointer now pointing to the last entry read is incremented by one. APB bridge 235 returns the recorded entry to MP 240 bus master and it increments it's read count. After buffer 4313 is read, the same process is applied to buffers 4314 and 4315.

[0207] Figure 45 shows a flow diagram of executable process steps in history module 207 for recording bus transactions in system 200, according to one aspect of the present invention.

[0208] Turning in detail to Figure 45, is step S4500, the process sets up registers for recording. Field 4300A is set to"EnableRcrdReg" (also referred to as"EnRcrdReg"in Figure 43) to record transactions.

[0209] In step S4501, the process determines if field 3300E is set to enable any break point testing. Field 3300J in register 3300 may be used to specify break point conditions.

[0210] In step S4502, transactions are recorded. Bus (208 and 236) transactions are recorded when EnableRcrdReg field 4300 is set. Signals HREADY 307 and PENABLE 1603 are sampled by Mux 4324. The signals indicate that a valid transaction is on the bus that may be recorded unless masked by field 3300A. When an entry is made in buffers 4313-4315, pointer 3501 is updated. When history module 234 stops making entries in buffers 4313-4315, the value of 3501 points to the last entry plus one.

[0211] In step S4503, based on whether break point condition testing is enabled, history module 234 tests for break point conditions. Based on the setting of EnBPStp 3300E, history module 234 may continue or stop break point condition testing after a particular break point is encountered.

[0212] In step S4504, the process determines the value of TM field 3300G. This sets the amount of data that is to be recorded after a break point condition is detected. It is noteworthy that steps S4502-4504 may occur simultaneously.

[0213] In step S4505, recording is stopped and field 4300A is cleared.

[0214] In step S4506, recorded information is extracted.

MP 240 bus master (not shown) reads the history address buffer 4313 and history module 234 places the recorded entry into register 4327 (Figure 44A) and history stack

pointer 3501 is incremented by one. APB bridge 235 returns the recorded entry to MP 240 bus master and it increments its'read count. After buffer 4313 is read, the same process is applied to buffers 4314 and 4315.

[0215] In one aspect of the present invention, history module 234 provides visibility to transactions on the internal AHB Bus 236 or APB Bus 208.

[0216] In one aspect of the present invention, history module 234 selects specific slave or peripheral transactions for recording based on a slave or peripheral mask. This allows selective monitoring of system 200 components.

[0217] In yet another aspect of the present invention, the process described above provides break point conditions for stopping History module 234 recording.

However, external break point signal may be continually provided after recording stops. In addition, break point conditions may be provided for an Address/Data break point and an Address Range break point.

[0218] In another aspect of the present invention, an external analyzer is not required to record bus transactions. This saves pins and the effort required connecting system 200 to an external device so that its components can be monitored.

[0219] Firmware Synchronization :

[0220] DSPIM 210 provides an interface for communication between MP 240 and DSP 229 as a bridge between APB bus 208 and DSPAHB bus 233. DSPIM 210 provides an IN/OUT register f file for passing command and status parameters between MP 240 and DSP 229. Figure 46 and 47 show registers that are used for MP 240 and DSP 210 to communicate with each other. Register 4600 and 4700 are addressable from APB bus 208 and DSPAHB bus 233. Registers 4600 and 4700 provide a"mail box"for exchange of information between MP 240 and DSP 229. Register 4600 can be read and written by MP 240. MP 240 can only read register 4700, while DSP 229 may read or write. An attempt by MP 240 to write into register 4700 results in declaration of"address exception"by DSPIM 210. Contents of registers 4600 and 4700 are based on firmware and user defined parameters.

[0221] MP 240 writes in register 4600 and interrupt is sent to DSP 229. MP 240 sets field 4900C in status register 4900, which generates an interrupt to DSP 229.

[0222] Figure 50 shows a flow diagram of communication between MP240 and DSP 229 using IN/Out registers 4600 and 4700, respectively.

[0223] In step S5000, MP 240 send information to DSP 229.

[0224] In step S5001, MP240 writes the information (or address of the information) in register 4600.

[0225] In step S5002, MP 240 sets field 4900C and generates an interrupt for DSP 229.

[0226] In step S5003, DSP 229 services the interrupt by reading register 4600 and clears field 4900C.

[0227] In step S5004, register 4600 is again available for MP 240 to write into register 4600.

[0228] DSPIM 210 is operationally coupled to memory module 212 via interface 230. MP240 and DSP 229 for storing firmware control instructions and any other information may use memory module 212. Interface 230 allows APB bus 208 to access memory module 212 while DSPIM 210 executes firmware instructions.

[0229] Memory module 212 is shared using registers 4600, 4700 and semaphore register 5100 shown in Figure 51.

Semaphore register 5100 field 5100A provides firmware interlock when MP 240 acquires the semaphore. Semaphore register 5100 field 5100B provides hardware interlock when MP 240 acquires the semaphore. DSP 229 cannot execute a write access to any register except register 5100 or a status register.

[0230] Memory module 212 uses an indirect access register 5200 that facilitates communication between DSP 229 and MP 240 without using any counters. Memory module 212 uses at least a FIFO buffer from where data may be read and/or written. Memory module 212 uses register 5300 (Figure 53) that includes FIFO data. MP 240 sets up field 5200A that allows indirect access. Field 5200G indicates the starting

address of memory module 212. Each access to register 5300 updates field 5200G.

[0231] An indirect read transaction may be initiated by setting up field 5200A and 5200C. Each time register 5300 is accessed, the address in field 5200F is updated. If field 5200C is set then it indicates that the read access is a sequence of continual read accesses that keeps memory module 212 FIFO (not shown) full.

[0232] An indirect write access may be initiated by setting field 5200A and 5200B. After the indirect access, register 5300 is updated with data that is written into memory module 212. Each time data is written into register 5300, DSPIM 210 writes data into memory module 212.

[0233] One advantage of providing the mail-box"concept is that no write conflict occurs between MP 240 and DSP 229.

[0234] In one aspect, MP 240 and/or DSP 229 do not have to gain ownership and then relinquish ownership (clear) of any registers to communicate with each other. This saves performance time and improves overall efficiency, because the registers are dedicated.

[0235] In another aspect of the present invention, indirect access is available to access memory module 212.

[0236] In another aspect of the present invention, the IN/Out mailbox environment may be used to efficiently run

test cases. MP 240 using Assembler or any other language may run test cases. A sub-set of test instructions may be executed by DSP 229. The mailboxes have a buffer (not shown) that keeps a real-time picture of a test case.

When the test is complete, mail-boxes are unloaded and a report may be generated that can be used for bug fixing and analysis.

[0237] Although the present invention has been described with reference to specific embodiments, these embodiments are illustrative only and not limiting. Many other applications and embodiments of the present invention will be apparent in light of this disclosure and the following claims.