Zero Length Descriptor - 2.0 English

Versal Adaptive SoC DMA and Bridge Subsystem for PCI Express Product Guide (PG344)

Document ID
Release Date
2.0 English

The length field in a descriptor can be zero. In this case, the H2C Stream Engine will issue a zero byte read request on PCIe. After the QDMA receives the completion for the request, the H2C Stream Engine will send out one beat of data with tlast on the QDMA H2C AXI4-Stream interface. The zero byte packet will be indicated on the interface by setting the zero_b_dma bit in the tuser. The user logic must set both the SOP and EOP for a zero byte descriptor. If not done, an error will be flagged by the H2C Stream Engine.