The following table includes details of the transmit buffer descriptor list.
|31:0||Byte address of buffer.|
|31||Used: must be zero for the controller to read data to the transmit buffer. After it is successfully transmitted, the controller sets this bit to one for the first buffer of a frame. Software must clear this bit before the buffer can be used again.|
|30||Wrap: marks last descriptor in the transmit buffer descriptor list. This can be set for any buffer within the frame.|
|29||Retry limit exceeded, transmit error detected.|
|28||Always set to 0.|
|27||Transmit frame corruption due to AXI error: set if an error occurs midway while reading through the transmit frame from the AXI, including RESP errors, and buffers exhausted mid-frame. If the buffers run out during transmission of a frame, then transmission stops, the FCS is incorrect, and tx_er is asserted.|
|26||Late collision, transmit error detected. Late collisions force this status bit to be set in gigabit mode.|
|23||For extended buffer descriptor mode. This bit indicates a timestamp is captured in the buffer descriptor. Otherwise the bit is reserved.|
Transmit IP/TCP/UDP checksum generation offload errors:
No CRC to be appended by the MAC. When set this bit implies that the data in the buffers already contains a valid CRC and no CRC or padding is appended to the current frame by the MAC.
This control bit must be set for the first buffer in a frame and is ignored for the subsequent buffers of a frame. This bit must be clear when using the transmit IP/TCP/UDP checksum generation offload, otherwise checksum generation and substitution does not occur.
|15||Last buffer, this bit (when set) indicates that the last buffer in the current frame is reached.|
|13:0||Length of buffer.|
|64-bit Addressing for AXI DMA Interface||32-bit Addressing for External FIFO Interface||Field||Description|
|Word 0||Word 0||31:0||Byte address of buffer|
|Word 1||Word 1||31:0||Miscellaneous fields|
|Word 2||-||31:0||Upper 32-bit address of the data buffer|
|Word 3||Word 2||31:0||Not used|
|Word 4||Word 3||
Timestamp seconds [1:0]