SPRUJ53B April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
In this mode, all channels have equal priority and each enabled channel is serviced in round-robin fashion as:
CH1 → CH2 → CH3 → CH4 → CH5 → CH6 → CH1 → CH2 → … |
In the case above, after each channel has transferred a burst of words, the next channel is serviced. The user can specify the size of the burst for each channel. Once CH2CH6 (or the last enabled channel) has been serviced, and no other channels are pending, the round-robin state machine enters an idle state.
From the idle state, channel 1 (if enabled) is always serviced first. However, if the DMA is currently processing another channel x, all other pending channels between x and the end of the round are serviced before CH1. All the channels are of equal priority. For instance, take an example where CH1, CH4, and CH5 are enabled in round-robin mode and CH4 is currently being processed. Then CH1 and CH5 both receive an interrupt trigger from the respective peripherals before CH4 completes. CH1 and CH5 are now both pending. When CH4 completes the burst, CH5 is serviced next. Only after CH5 completes a burst is CH1 serviced. Upon completion of the CH1 burst, if there are no more channels pending, the round-robin state machine enters an idle state.
A more complicated example is:
The round-robin state machine can be reset to the idle state using the DMACTRL[PRIORITYRESET] bit.