Method of executing concurrent tasks by a subsystem managed by a central processor

• US 20040268355A1
• Filed: 04/23/2004
• Published: 12/30/2004
• Est. Priority Date: 04/24/2003
• Status: Active Grant

• Current Assignee: Stmicroelectronics France (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Inventors: Robin, Frederic, Artieri, Alain, Lefftz, Vincent, Audrain, Stephane, Dumarest, Jacques
• Granted Patent: US 7,797,700 B2
• Time in Patent Office: Days
• US Class Current: 718/100
• CPC Class Codes: G06F 9/52 Program synchronisation; Mutual exclusion, e.g. by means of semaphores
• CPC Class Codes: H04N 19/42 characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation H04N19/635 takes precedence

Abstract

Systems and methods are provided for processing different concurrent tasks by a subsystem managed by a central processor. Each tasks is comprised of successive messages including a first message, intermediate messages, and a last message. Each intermediate message comprises a subtask parameter and a link to the next message that indicates the time when the next message is to be processed. The central processor and the subsystem are connected to a storage memory and several counters associated with respective tasks. The system and method reduce task disruptions of the system.

Claims

1. A method of processing concurrent tasks by a subsystem managed by a central processor, each of the tasks being comprised of successive messages including a first message, intermediate messages, and a last message, each of the intermediate messages comprising at least one subtask parameter and a link to the next message that indicates a time of processing of the next message, the method comprising, for each task, the steps of:

writing by the central processor, the writing step including the sub-steps of;

writing a message in a memory;

if a counter is initially free for access, prohibiting access to the counter by the subsystem, and then;

if the counter has a zero value, writing in the subsystem a link that indicates a time of processing of the first message by the subsystem;

otherwise, writing in the subsystem a link to the next message, the link to the next message being included in the message written in the memory;

incrementing the counter by a number representative of presence of the message of the task in the memory; and

ending the prohibition against accessing the counter; and

processing by the subsystem, the processing step including the sub-steps of;

if the counter is initially free for access, prohibiting access to the counter by the central processor;

if the counter has a non-zero value, reading the link to the next message and decrementing the counter;

ending the prohibition against accessing the counter; and

processing the subtask parameters of the next message at the time indicated in the link to the next message.

2. The method according to claim 1, wherein the link to the next message also indicates a length of the next message.

3. The method according to claim 1, wherein the messages of one task are arranged sequentially in the memory.

4. The method according to claim 3, wherein the link to the next message does not include an address of the next message in the memory.

5. The method according to claim 1, wherein the link to the next message also indicates an address of the next message in the memory.

6. The method according to claim 5, wherein the writing step further includes the sub-step of:

prior to the sub-step of writing the message in the memory, consulting a list of available addresses in the memory, determining an address at which to store the message in the memory, and writing the address of the message in the link of the preceding message.

7. The method according to claim 1, wherein the link to the next message also indicates a type of the next message.

8. The method according to claim 7, wherein the link to the next message is capable of indicating an immediate processing of the next message.

9. The method according to claim 8, wherein the link to the next message is capable of indicating processing conditioned by an external event.

10. The method according to claim 9, wherein the processing step further includes the sub-step of:

receiving a video synchronization signal representative of an external event, and then processing the next message.

11. The method according to claim 1, wherein the link to the next message indicates the time of processing the next message by a relative time interval separating the processing of the next message and processing of the message comprising the link to the next message.

12. The method according to claim 1, wherein the first message of the task does not include subtask parameters.

13. The method according to claim 12, wherein the last message of the task comprises a link indicating end of the task.

14. The method according to claim 13, wherein the indication of the time of processing of the next message in the last message comprises a zero value.

15. The method according to claim 1,

wherein the subsystem executes video processing tasks comprising the management of image acquisition, the management of image display, and image encoding/decoding, and

when two or more links indicate the same time of processing the next message, the subsystem gives priority to processing the subtask parameters of an image acquisition management message, then to the subtask parameters of an image display message, and then to the subtask parameters of an image encoding/decoding message.

16. The method according to claim 1, further comprising the step of providing a common clock signal to the subsystem and the central processor, each of the subsystem and the central processor determining its system time based on the common clock signal.

17. The method according to claim 16, wherein the processing of parameters of a message is performed when the system time of the subsystem is equal to the time indicated for the processing of the message.

18. An electronic system for executing concurrent tasks, the system comprising:

a storage memory;

a central processor capable of generating and writing messages of the concurrent tasks in the storage memory, each of the tasks being comprised of a first message, a plurality of intermediate messages, and a last message, and each intermediate message comprising at least one subtask parameter and a link to the next message;

a subsystem capable of reading the messages from the storage memory, the subsystem comprising command means for requesting the processing of one of the messages at the time specified in the link of the preceding message, and processing means for processing the message in response to the request;

a plurality of counters, each of the counters being associated with one of the tasks, being capable of being incremented by the central processor, and being capable of being decremented by the subsystem; and

semaphores associated with the counters, each of the semaphores authorizing an access by the central processor to the counter associated with that semaphore only in the absence of an access by the subsystem to that counter, and authorizing an access by the subsystem to the associated counter only in the absence of an access by the central processor to that counter.

19. The system according to claim 18, wherein the memory comprises at least a plurality of FIFO-type parallel storage lines, the input of each line being connected to the central processor and the output of each line being connected to the subsystem.

20. The system according to claim 18, further comprising a clock supplying a single clock signal to the central processor and the subsystem.

21. The system according to claim 20, wherein the central processor and the subsystem each include means for determining a system time as a function of the single clock signal.

22. The system according to claim 21, wherein the subsystem comprises a time module for comparing the system time and the time of processing of a message, and for generating the request upon an equality between the system time and the time of processing.

23. The system according to claim 18, wherein the subsystem includes an input for receiving external events other than clock signals.

24. The system according to claim 23, wherein the subsystem includes means for synchronizing the processing of at least one message with a received external event.

25. The system according to claim 18, wherein one of the counters comprises the number of messages of one of the tasks stored in the memory.

26. A machine-readable medium encoded with a program for processing concurrent tasks by a subsystem managed by a central processor, each of the tasks being comprised of successive messages including a first message, intermediate messages, and a last message, each of the intermediate messages comprising at least one subtask parameter and a link to the next message that indicates a time of processing of the next message, the program containing instructions for performing, for each task, the steps of:

writing by the central processor, the writing step including the sub-steps of;

writing a message in a memory;

if a counter is initially free for access, prohibiting access to the counter by the subsystem, and then;

if the counter has a zero value, writing in the subsystem a link that indicates a time of processing of the first message by the subsystem;

otherwise, writing in the subsystem a link to the next message, the link to the next message being included in the message written in the memory;

incrementing the counter by a number representative of presence of the message of the task in the memory; and

ending the prohibition against accessing the counter; and

processing by the subsystem, the processing step including the sub-steps of;

if the counter is initially free for access, prohibiting access to the counter by the central processor;

if the counter has a non-zero value, reading the link to the next message and decrementing the counter;

ending the prohibition against accessing the counter; and

processing the subtask parameters of the next message at the time indicated in the link to the next message.

27. The machine-readable medium according to claim 26, wherein the messages of one task are arranged sequentially in the memory.

28. The machine-readable medium according to claim 26, wherein the link to the next message indicates the time of processing the next message by a relative time interval separating the processing of the next message and processing of the message comprising the link to the next message.

29. The machine-readable medium according to claim 26, wherein the program further contains instructions for performing the step of providing a common clock signal to the subsystem and the central processor, each of the subsystem and the central processor determining its system time based on the common clock signal.