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algorithm. 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.The framework preempts Algorithm A to run algorithm B. Algorithm A'sdata transfer is aborted to free the DMA channel to Algorithm B.
3.Algorithm B requests a data transfer by calling ACPY2_start(). The framework executes this request immediately since the DMA channel is free.
4.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.
5.The framework returns control to Algorithm A and also restarts the data transfer that was aborted in Event #2.
6.Algorithm A calls ACPY2_wait() to wait for the data transfer to complete. The framework checks to see that data is still being transferred.
7.The data transfer is complete and the framework returns control to Algorithm A so it can process the transferred data.
Scenario 1 can result in algorithm A waiting for the DMA transfer to complete longer than necessary because of the abort/restart policy. However, in this scenario it is more important to grant the DMA channel to the higher priority algorithm.
∙Scenario 2: The system policy is to let the current DMA transfer issued by the lower priority algorithm finish before starting a DMA transfer issued by the higher priority algorithm. See Section 6.15.5.
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CPU context |
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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 B requests a data transfer by calling ACPY2_start(). Note that the framework has preempted Algorithm A to run algorithm B. Algorithm A'sdata transfer is still in progress, so algorithm B'stransfer will be delayed.
3.Algorithm A'sdata transfer has completed and Algorithm B'sdata transferred request can be executed.
4.Algorithm B calls ACPY2_complete() to check if the data transfer has completed. The framework checks to see that data is still being transferred.
5.Algorithm B calls ACPY2_complete() to check if the data transfer has completed. The framework checks to see that data transfer has completed. Algorithm B can process the transferred data.
6.Algorithm A calls ACPY2_wait() to wait for the data transfer to complete. The framework checks to see that data transfer has completed. The framework returns control to Algorithm A so it can process the transferred data.
Scenario 2 can result in a delay of the data transfer for algorithm B since the transfer for algorithm A might still be active.
SPRU352G | Use of the DMA Resource | 73 |
