Prior to starting CDMA Scatter Gather operations, the software application must set up a transfer descriptor chain. After the AXI CDMA begins SG operations, it fetches, processes, and then updates the descriptors. By analyzing the descriptors, the software application can track the status of the associated CDMA data transfer and determine the completion status of the transfer. With this information, the software application can manage the transfer.
The act of writing to the TAILDESC register causes the AXI CDMA hardware, if it is paused at the tail pointer, to begin processing descriptors again.
If the AXI CDMA hardware is not paused at the TAILDESC pointer, writing to the TAILDESC register (TAILDESC_MSB when in 64 bit mode) makes AXI CDMA continue to process descriptors until it reaches the new tail descriptor pointer location.