SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
Chaining is a mechanism by which the completion of one transfer automatically sets the event for another channel. When a chained completion code is detected, the value of which is dictated by the transfer completion code EDMA_TPCC_OPT_n[17:12] TCC of the PaRAM set associated with the channel, it results in the corresponding bit in the chained event register EDMA_TPCC_CER to be set EDMA_TPCC_CER[31:0] E[TCC] = 1).
Once a bit is set in EDMA_TPCC_CER, the EDMA_TPCC prioritizes and queues the event in the appropriate event queue. When the event reaches the head of the queue, it is evaluated for submission as a transfer request to the transfer controller.
As in the event-triggered transfers, if the PaRAM set associated with the channel is valid (it is not a null set) then the TR is submitted to the associated EDMA_TPTC and the channel can be triggered again.
If the PaRAM set associated with the channel is a NULL set (see Section 16.2.4.3.3 Null PaRAM Set), then no transfer request (TR) is submitted and the corresponding EDMA_TPCC_CER[31:0] En bit is cleared and simultaneously the corresponding channel bit is set in the event miss register EDMA_TPCC_EMR[31:0] En = 1 to indicate that the event was discarded due to a null TR being serviced. In this case, the error condition must be cleared before the DMA channel can be re-triggered. Good programming practices might include clearing the event missed error before re-triggering the DMA channel.
If a chaining event is being processed (prioritized or queued) and another chained event is received for the same channel prior to the original being cleared EDMA_TPCC_CER[31:0] En != 0), then the second chained event is registered as a missed event in the corresponding channel bit of the event missed register EDMA_TPCC_EMR[31:0] En = 1.
Chained event registers EDMA_TPCC_CER, event registers EDMA_TPCC_ER, and event set registers EDMA_TPCC_ESR operate independently. An event En can be triggered by any of the trigger sources (event-triggered, manually-triggered, or chain-triggered).