11.1.6 Channel Priority

Each DMA channel functions independently of the others, but also competes with the others for access to the data and DMA buses. When access collisions occur, the DMA Controller arbitrates between the channels using a user-selectable priority scheme. Two schemes are available:

• Round Robin: When two or more channels collide, the lower numbered channel receives priority on the first collision. On subsequent collisions, the higher numbered channels each receive priority based on their channel number.
• Fixed: When two or more channels collide, the lowest numbered channel always receives 
priority, regardless of past history; however, any channel being actively processed is not available for an immediate retrigger. If a higher priority channel is continually requesting service, it will be scheduled for service after the next lower priority channel with a pending request.