SWCU192 November 2021 CC1312R7 , CC1352P7 , CC2652P7 , CC2652R7
When a μDMA channel requests a transfer, the μDMA controller arbitrates among all the channels making a request, and services the μDMA channel with the highest priority. Once a transfer begins, it continues for a selectable number of transfers before rearbitrating among the requesting channels. The arbitration size can be configured for each channel, ranging from 1 to 1024 item transfers. After the μDMA controller transfers the number of items specified by the arbitration size, the controller then checks among all the channels making a request, and services the channel with the highest priority.
If a lower-priority μDMA channel uses a large arbitration size, the latency for higher-priority channels is increased because the μDMA controller completes the lower-priority burst before checking for higher-priority requests. Therefore, lower-priority channels must not use a large arbitration size for best response on high-priority channels.
The arbitration size can also be thought of as burst size. Arbitration size is the maximum number of items that are transferred at any one time in a burst. Here, the term arbitration refers to the determination of the μDMA channel priority, not arbitration for the bus. When the μDMA controller arbitrates for the bus, the processor always takes priority. Furthermore, the μDMA controller is delayed whenever the processor must perform a bus transaction on the same bus, even in the middle of a burst transfer.