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.