Handling Descriptors With Errors - 4.0 English

QDMA Subsystem for PCI Express Product Guide (PG302)

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4.0 English

If an error is encountered while fetching a descriptor (in pre-fetch or regular mode), the QDMA Descriptor Engine flags the descriptor with error. For a queue in internal mode, the C2H Stream Engine handles the error descriptor by not performing any PCIe or DMA activity. Instead, it waits for the error descriptor to pass through the pipeline and forces a writeback after it is done. For a queue in bypass mode, it is the responsibility of the user logic to not issue a batch of descriptors with an error descriptor. Instead, it must send just one descriptor with error input asserted on the C2H Stream bypass-in interface and set the SOP, EOP, no_dma signal, and sdi or mrkr_req signal to make the C2H Stream Engine send a writeback to Host.