GTS AXI Multichannel DMA IP for PCI Express* User Guide
A.1.1.2.1. D2H Descriptor Fetch
When you enable multiple DMA channels in AXI-S mode, the GTS AXI MCDMA IP limits the number of the channels that can be active or can prefetch the descriptors for the data movement to avoid implementing the larger memory to hold descriptors simultaneously for all channels.
The descriptor FIFO is designed to hold descriptors only for a defined number of channels. When the data is received on the user interface, there is no handshake between the host software and User Logic through the GTS AXI MCDMA IP to control the order of descriptor fetch or data movement of multiple channels. To enable easy access to descriptors of multiple channels, the GTS AXI MCDMA IP implements segmentation of the descriptor FIFO.
In AXI-S mode, when data is received for a channel that does not have Tail pointer (TID) updates from the host, the corresponding AXI-Stream packet from SOF to EOF is dropped.