Texas Instruments TMS320 DSP manual Preemptive System

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Inter-Algorithm Synchronization

Algorithm A

Algorithm B

CPU context

active

active

(timeline)

1

2

3

4

5

DMA context

(timeline)

DMA/CPU idle

CPU context switch

CPU/DMA active

Events

1.Algorithm A requests a data transfer by calling ACPY2_start(). The framework executes this request immediately since the DMA channel is free.

2.Algorithm A calls ACPY2_wait() to wait for the data transfer to complete. The framework checks to see that the data are still being transferred.

3.The data transfer is complete and the framework returns control to Algorithm A so it can process the transferred data.

4.Algorithm B requests a data transfer by calling ACPY2_start().The framework executes this request immediately since the DMA channel is free.

5.Algorithm B calls ACPY2_complete() to check if the data transfer has completed. The framework checks to see that the data has been transferred. Algorithm B can process the transferred data.

Notice that algorithm A must wait for the transfer to complete because the parallel CPU processing takes less time than the data transfer, whereas algorithm B'sdata transfer has completed at the time of synchronization.

In summary, we can see from Section 6.15.2 that sharing a physical DMA channel between several algorithms is trivial as long as the algorithms don'tpreempt each other.

6.15.3 Preemptive System

Sharing a physical DMA channel among two algorithms in a preemptive system requires some procedure to manage the shared resource. The system must have a policy for handling the situation where one algorithm preempts another algorithm while the shared physical DMA channel is currently being used.

Let'sassume that the framework preempts algorithm A in order to run algorithm B.

∙Scenario 1: The system policy is to abort the current DMA transfer to free-up the DMA device to the higher priority algorithm. See Section 6.15.4.

Algorithm A			Algorithm B		Algorithm A
active			active			active
CPU context
(timeline)
1	2	3	4	5	6	7
DMA context
(timeline)

DMA/CPU idle

CPU context switch

CPU/DMA activ

The system'spolicy is to abort the current DMA transfer when context switching to a higher priority

72

Use of the DMA Resource

SPRU352G –June 2005 –Revised February 2007

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Contents Users Guide Rules and GuidelinesSubmit Documentation Feedback Contents Use of the DMA Resource Urls List of Figures Read This First Intended AudienceDocument Overview Related Documentation Text ConventionsRule n Guideline nOverview Scope of the Standard Rules for TMS320C5x Rules for TMS320C6xRules and Guidelines Requirements of the StandardGoals of the Standard Intentional OmissionsSystem Architecture FrameworksAlgorithms Core Run-Time SupportGeneral Programming Guidelines Use of C Language Threads and ReentrancyThreads RulePreemptive vs. Non-Preemptive Multitasking ReentrancyExample Data Memory Data MemoryMemory Spaces Scratch versus PersistentScratch vs Persistent Memory Allocation Algorithm versus Application GuidelineProgram Memory ROM-abilitySection Name Purpose Use of Peripherals Use of PeripheralsAlgorithm Component Model Interfaces and Modules Algorithms PackagingInterfaces and Modules Implementation Fir.hExternal Identifiers Naming Conventions Module Initialization and FinalizationModule Instance Objects Design-Time Object Creation Run-Time Object Creation and DeletionModule Configuration Example ModuleMultiple Interface Support Interface Inheritance SummaryElement Description RequiredAlgorithms AlgorithmsPackaging Object CodeHeader Files Debug Verses ReleaseModuleversvendorvariant.1arch Algorithm Performance Characterization Data Memory Program Memory Interrupt Latency Execution TimeHeap Memory ExternalSize Stack Memory Static Local and Global Data MemoryData Bss Object files Size Interrupt Latency Execution TimeMips Is Not Enough OperationExecution Time Model Execution Timeline for Two Periodic TasksProcess 19800059000 198000 Submit Documentation Feedback DSP-Specific Guidelines CPU Register Types Register TypesUse of Floating Point TMS320C6xxx Rules and GuidelinesEndian Byte Ordering Data ModelsRegister Conventions Status RegisterRegister Use Type CSR Field Use TypeInterrupt Latency TMS320C54xx Rules and GuidelinesProgram Models TMS320C54xx Rules and Guidelines Status Registers ST0 Field Name Use TypeST1 Field Name Use Type TMS320C55x Rules and Guidelines Stack ArchitecturePmst Field Name Use Type Relocatability ExampleSSP Status Bits ST2 Field Name Use TypeST3 Field Name Use Type Homy TMS320C24xx Guidelines GeneralTMS320C28x Rules and Guidelines TMS320C28x Rules and GuidelinesXAR0 M0M1MAP Use of the DMA Resource Submitting DMA Transfer RequestsOverview Algorithm and FrameworkRequirements for the Use of the DMA Resource Logical ChannelData Transfer Properties Data Transfer SynchronizationAbstract Interface DMA GuidelineDMA Rule Resource Characterization Data Transfers bytes FrequencyAverage Maximum Runtime APIs Strong Ordering of DMA Transfer RequestsSubmitting DMA Transfer Requests Device Independent DMA Optimization GuidelineCache Coherency Issues for Algorithm Producers 13 C6xxx Specific DMA Rules and GuidelinesSupporting Packed/Burst Mode DMA Transfers 14 C55x Specific DMA Rules and GuidelinesMinimizing Logical Channel Reconfiguration Overhead Addressing Automatic Endianism Conversion IssuesInter-Algorithm Synchronization Non-Preemptive SystemPreemptive System Algorithm B Algorithm a Inter-Algorithm Synchronization Appendix a General Rules Performance Characterization Rules DMA RulesGeneral Guidelines DMA Guidelines Submit Documentation Feedback DSP/BIOS Run-time Support Library Core Run-Time APIsDSP/BIOS Run-time Support Library TI C-Language Run-Time Support LibraryBibliography BooksSubmit Documentation Feedback Glossary Glossary of TermsGlossary of Terms Glossary of Terms Important Notice