Descriptor Bypass - 3.4 English

Versal Adaptive SoC CPM DMA and Bridge Mode for PCI Express Product Guide (PG347)

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3.4 English

The descriptor fetch engine can be bypassed on a per channel basis through AMD Vivado™ IDE parameters. A channel with descriptor bypass enabled accepts descriptor from its respective c2h_dsc_byp or h2c_dsc_byp bus. Before the channel accepts descriptors, the Control register Run bit must be set. The NextDescriptorAddress and NextAdjacentCount, and Magic descriptor fields are not used when descriptors are bypassed. The ie_descriptor_stopped bit in Control register bit does not prevent the user logic from writing additional descriptors. All descriptors written to the channel are processed, barring writing of new descriptors when the channel buffer is full.

When XDMA is configured in descriptor bypass mode, there is an 8 deep descriptor FIFO which is common for all descriptor channels from user.