For host-to-card transfers, data is read from the host at the source address, but the
destination address in the descriptor is unused. Packets can span multiple descriptors.
The termination of a packet is indicated by the EOP control bit. A descriptor with an
EOP bit asserts tlast on the AXI4-Stream user
interface on the last beat of data.
Data delivered to the AXI4-Stream interface will be packed for each descriptor. tkeep is all 1s except for the last cycle of a data transfer of the descriptor if it is not a multiple of the datapath width. The DMA does not pack data across multiple descriptors.