Data transactions on the AXI write channel can only be controlled using the flow-control interface (FCI). The FCI is implemented per channel to provide read/write access flow control ability to the PL slave. The FCI can be independently controlled from each channel's control register. Software configures what accesses are flow controlled by the FCI (read/write).
The PL slave provides credits to the DMA channel. Each credit is a permission for a single AXI transaction. When the FCI is attached to the SRC (read), there is a permission to generate one AXI data read transaction (write transaction when FCI is attached to DST (write)). Table: Flow Control Interface Signals lists the FCI signals.
IMPORTANT: The maximum number of credits accepted are 32.
The timing diagram for the flow control interface is as shown in This Figure.
Software can configure FCI to flow control either the SRC or DST based on whether the DMA channel is reading from or writing to the PL slave.
•FCI must be configured to flow control SRC if the DMA is reading from the PL slave.
•FCI must be configured to flow control DST if the DMA is writing to the PL slave.