Scatter Gather Transfer Descriptor Definition - 4.1 English

This defines the format and contents of the AXI CDMA Scatter Gather Transfer Descriptors. These are used only by the SG function if it is enabled in the CDMA and the CDMACR.SGMode bit is set to 1. A transfer descriptor consists of eight 32-bit words. The descriptor represents the control and status information needed for a single CDMA transfer plus address linkage to the next sequential descriptor. Each descriptor can define a single CDMA transfer of up to 67,108,863 Bytes of data. A descriptor chain is defined as a series of descriptors that are sequentially linked through the address linkage built into the descriptor format.

The AXI CDMA SG Engine traverses the descriptor chain following the linkage until the last descriptor of the chain (descriptor defined by TAILDESC) has been completed. The relationship and identification of the AXI CDMA transfer descriptor words is shown in the following table.

Note:   Transfer Descriptors must be aligned on 16 32-bit word alignment. Example valid offsets are 0x00, 0x40, 0x80, and 0xC0.