Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 7/19/2024
Public

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5.1.7.9. Switching to a New Descriptor List in the Receive DMA

Switching to a new descriptor list is different in the RX DMA as compared to TX DMA. Switching to a new descriptor list is permitted when the RX DMA is in SUSPEND state. This is because:
  • Generally, the RX DMA prepares the descriptors in advance.
  • If the RX DMA goes to SUSPEND mode due to descriptors being unavailable, it is a major failure (software is not able to free the filled-up descriptors/buffers) and if not rectified immediately, it leads to loss of frames due to RX FIFO overflow. The software is allowed to create a new descriptor list and program the RX DMA to start using it immediately, without going into STOP state.