22.6.3.1.3 Adding a Descriptor Between Existing Descriptors

To insert a new descriptor 'C' between two existing descriptors ('A' and 'B'), the descriptor currently executed by the DMA must be identified.

1. If DMA is executing descriptor B, descriptor C cannot be inserted.
2. If DMA has not started to execute descriptor A, follow the steps:
   1. Set the descriptor A VALID bit to ‘0’.
   2. Set the DESCADDR value of descriptor A to point to descriptor C instead of descriptor B (see DESCADDR in the DMAC Register Summary from Related Links).
   3. Set the DESCADDR value of descriptor C to point to descriptor B (see DESCADDR in the DMAC Register Summary from Related Links).
   4. Set the descriptor A VALID bit to ‘1’.
3. If DMA is executing descriptor A:
   1. Apply the software suspend command to the channel and
   2. Perform steps 2.1 through 2.4.
   3. Apply the software resume command to the channel.