METHOD AND APPARATUS FOR ENFORCING INDEPENDENCE OF PROCESSORS ON A SINGLE IC

Field of the Invention

The present invention relates generally to embedded systems and more specifically to the field of enforcing independence of processors on a single Integrated Circuit (IC).

Background of the Invention

In the field of embedded systems, systems are sometimes required to exhibit a high level of reliability and fault tolerance. A high level of reliability and fault tolerance is typically achieved through the use of redundant processing techniques. For example, a redundant processor may provide continuous verification of a main processor and may be included to achieve a high level of reliability and fault tolerance of the system. In such a case, it is important that the redundant processor be truly independent and unable to affect the output of the main processor, or else the redundant processor will need verification itself. In many cases, the redundant processor is a device that is specifically designed to perform error detection. ^: Having two processors is effective, but has the disadvantage of requiring additional physical components. Having additional physical components often increases the cost and design difficulty. Further, having two processors may not be easily adaptable to new applications, since the redundant processor may need to be redesigned each time new functionality is added.

Despite these disadvantages, many solutions utilize two general purpose microprocessors and many solutions place two microprocessor cores on a single Integrated Circuit (IC). One typical design is a single IC with two microprocessor cores where each processor has its own system bus, memories and embedded peripherals. A second typical design is a single IC with two microprocessor cores, a shared system bus, memories and peripherals, where both microprocessor cores are allowed access to the memories and peripherals. Both of these typical designs have drawbacks, such as those mentioned above. In any case, existing typical designs are not suitable for systems that require a high level of reliability and fault tolerance.

Thus, there is a need for a single IC capable of adapting to a wide range of uses without complete duplication of all system memories and peripherals while still

having the ability to partition the system to create a main processing device and independent verifier.

Brief Description of the Figures

The present invention is illustrated by way of example and not limitation in the accompanying figures, in which like references indicate similar elements, and in which:

FIG. 1 is a block diagram illustrating a high assurance IC in accordance with an embodiment of the present invention.

FIG. 2 is a flow diagram illustrating a method for enforcing independence between processors in accordance with an embodiment of the present invention.

FIG. 3 is a table illustrating an example bus monitor configuration in accordance with an embodiment of the present invention.

FIG. 4 is a flow diagram illustrating an example method for enforcing independence for the example bus monitor configuration of FIG. 3. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. Detailed Description

Before describing in detail embodiments of the present invention, it should be observed that the present invention resides primarily in combinations of method steps and apparatus components. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a

process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises ...a" does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

FIG. 1 is a block diagram graphically illustrating the internal components of a single-chip integrated circuit (IC) 100 in accordance with one embodiment of the present invention. The single-chip IC 100 comprises a system- wide bus 101 equipped with a bus monitor 102 connected to an external alarm signal 107. The single-chip IC also includes two processors where processor A 103 is the main processor and processor B 104 acts as a monitor responsible for verifying the correct behavior of processor A and detecting any faults in the single-chip IC 100. Both processors 103, 104 are connected to the system wide bus 101 so that the processors 103, 104 can access embedded peripherals 105 and memories 106.

In one embodiment, each processor 103, 104 is capable of executing a plurality of applications independently of the other processor. In one embodiment, processor A 103 is an ARM9 processor available from ARM, LTD. Further, processor B 104 is an ARM7 processor available from ARM, LTD. Even though this description illustrates a single-chip IC 100 with two processors, the single-chip IC can comprise any number of processors. As such, the number two is not meant to be a limitation on any embodiment of the present invention. Further, as is known to one of ordinary skill in the art, having a single-chip IC with any number of processors is considered to be equivalent to the embodiment illustrated in FIG. 1.

In one embodiment, example embedded peripherals 105 include a SPI, an USART, a parallel port, and configurable registers. As is known to one of ordinary skill in the art, other such embedded peripherals may be included on the single-chip IC 100. For example, a timer, LFSR, etc. may be included on the single-chip IC 100. In one embodiment, example memories 106 include FLASH, SRAM, and

ROM. As is known to one of ordinary skill in the art, other such memories may be

included on the single-chip IC 100. For example, ROM, RAM, and other memories may be included on the single-chip IC 100.

The bus monitor 102 functions to enforce the independence of the two processors 103, 104 and the embedded peripherals 105 and memories 106 that the processors 103, 104 access. As used herein, enforcing the independence of the two processors 103, 104 means to enforce each processor's access rights to the embedded peripherals 105 and the memories 106. In one embodiment, enforcing independence of the two processors is accomplished by maintaining a table of address ranges that define access rights to the embedded peripherals 105 and the memories 106. In such an embodiment, the table maps access rights to the embedded peripherals 105 and the memories 106.

In any case, enforcing independence of the two processors means that the bus monitor validates bus accesses against its configuration. In one embodiment, if any disallowed accesses are attempted, the bus access is blocked and an alarm signal is activated, e.g. via alarm signal 107. In one embodiment, the activation of the alarm signal consists of an automatic write to a register internal to the device that causes an external electrical signal to be raised. Raising an external electrical signal may allow external devices to take actions necessary to contain the detected failure. In one embodiment, the bus monitor comprises mutually exclusive permissions so that only one processor has write access to the embedded peripherals and the memories. For example, processor A 103 may have read and write access to embedded peripherals 105 and memories 106, while processor B 104 may only have read access to embedded peripherals and memories. By allowing only one device to have write access to the embedded peripherals and the memories, independent subsystems are created in the single-chip IC 100.

FIG. 2 illustrates a method for enforcing independence between processors in accordance with an embodiment of the present invention. At step 202, a processor, e.g. processor A 103, requests access to an embedded peripheral or memory. Since the bus monitor 102 monitors the system- wide bus 101, the request is received by the bus monitor 102. Further, the request identifies an address that is associated with the embedded peripheral or the memory. For example, an embedded peripheral, such as a parallel port, may be accessed by address OxOOlO. If a processor, e.g. processor A

103, wants access to the parallel port, the request will contain the address 0x0010. At step 204, the bus monitor receives the request and compares the address contained in the request with its configuration to determine whether the processor should be allowed access to the address. In one embodiment, the configuration that the bus monitor utilizes for enforcing independence between the processors is a table that maps an embedded peripheral 105 or memories 106 to access rights for a given processor.

At Step 204, the bus monitor determines whether the address in the request is in a defined region in its configuration. If the address does not fall within one of the address ranges configured in the bus monitor (Step 204), the access is permitted (Step 210). If the address does fall within one of the configured address ranges (Step 204), the permissions associated with the address range are examined (Step 206). In one embodiment, the permissions are specific to a given processor. For example, processor A 103 may be able to write to address region #1, but processor B 104 may only be able to read to address region #1. If the requested access is not prohibited for the processor requesting the access (Step 206), then the access is allowed (Step 210). If the requested access is prohibited for the processor requesting access (Step 206), then the access is not allowed (Step 208). In one embodiment, if an access is not allowed, then an alarm signal, e.g. alarm signal 107) is activated. FIG. 3 illustrates an example bus monitor configuration. In this example, each processor is given specific access rights based upon the address region. For each address region, each processor may be given read, write and/or execute access independently of the other processor. For example, in FIG. 3, processor A 103 is given read and write access to address region #1 302, e.g. a block of SRAM memory. However, processor B 104 only has read access to address region #1 302. By allowing processor B 104 to read address region #1, processor B 104 is able to monitor and verify data being processed by processor A 103, without altering the operation of processor A 103. In such a manner, processor B 104 is able to verify the correct behavior of processor A 103 without affecting the operation of processor A 103.

Furthermore, the example configuration shows address ranges for address regions #2 304 and #3 306 which allow for both read and write access to an USART.

If address region #2 maps to a first USART and address region #3 maps to a second USART, then processor A is able to utilize the first USART while processor B is not able to utilize the first USART since it is assigned to processor A. In the example configuration of FIG. 3, the bus monitor is configured so that each processor is only permitted to use the USART assigned to it. In an embodiment, the receive line of the USART assigned to processor B 104 is externally connected to the transmit line of processor A 103's USART and the transmit functionality of the USART assigned to processor B 104 is physically disconnected so that it is not usable. By allowing processor B 104 access to processor A's USART, processor B 104 can verify the data being sent out of the single-chip IC 100.

FIG. 4 shows an example where a request by processor B 104 activates an alarm signal based upon the example configuration of FIG. 3. At step 402, processor B 104, attempts write access to address region #1 302. The bus monitor 102 processes the request for a write access and identifies address region #1 302 for the request. At step 404, the bus monitor receives the request and compares the address contained in the request with its configuration to determine whether processor B 104 should be allowed access to the address region #1 302. Since the address falls in one of the configured address ranges (Step 404), namely address region #1 302, the permissions associated with address range #1 302 are examined (Step 406). Since the requested access is prohibited for processor B 104, then the access is not allowed and an alarm signal is activated (Step 408).

In a further embodiment, a single-chip IC 100 may be configured to allow protection of sensitive data against misuse by untrusted software running on one of the processors. For example, the bus monitor may be configured to disallow the processor running the untrusted software access to the sensitive data and hence preventing unauthorized access to the sensitive data.

It will be appreciated that embodiments of the present invention described herein may be comprised of one or more conventional processors and unique stored program instructions that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions described herein. The non-processor circuits may include, but are not limited to, a radio receiver, a radio transmitter, signal drivers, clock circuits, power source circuits,

and user input devices. As such, these functions may be interpreted as steps of a method. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used. Thus, methods and means for these functions have been described herein. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.

In the foregoing specification, the invention and its benefits and advantages have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.