First byte of Ethernet preamble being replaced by XGMII start byte

[philn16]

Looking at test_axis_xgmii_rx_64.py, and testing axis_xgmii_rx_64.v it seems that current behavior ignores the first 8 XGMII bytes (including the start byte 0xFB). However, I'd expect it to ignore the first 9 XGMII bytes (including the start byte 0xFB) since the ethernet preamble + start of frame delimiter is 8 bytes.
Additionally, in xgmii_ep.py (which is used to test the XGMII Rx) the first byte is replaced by the XGMII start byte. That is, one of the preamble 0x55 bytes isn't sent through the XGMII.

dl[0] = XGMII_START
cl[0] = 1

I added a print out for d and c in xgmii_ep.py when running test_axis_xgmii_rx_64.py and got what's below. You can see 0x55 is only repeated 6 times instead of 7.

d is d5555555555555fb
c is 1

[philn16]

I've noticed the Xilinx MAC core does the same thing, so this is probably a non issue

[alexforencich]

The XGMII start character replaces the first preamble byte as per IEEE 802.3.

[alexforencich]

Specifically IEEE 802.3 46.2.2.