XGMII interface needs to send control codes

[nltcn]

Control codes cannot be sent out due to the _run requiring preamble to payload. When a local fault occurs on the receive side, we must advise link partner and restart sync with a control code.
Add a way to transmit control codes.

[alexforencich]

What control codes do you want to send? Ordered sets?

As far as I can tell, the local fault/remote fault ordered sets are only for indication, they have no effect over the actual link. CDR and block lock is completely independent of the data being sent over the link.

[nltcn]

When in local fault, the XGMII will output 0x0100009c with control mask 0x11. The system must send 0x0200009c with control mask 0x11 (yes, it is part of the ordered set) to let the link partner that it is not ready yet and that resync is required. Once local fault has been cleared, we can send the idle.

[alexforencich]

So you want to have the local fault/remote fault indication. What's the purpose? It has no effect on the operation of the actual link.

[alexforencich]

Ah sorry, I just realized this is the cocotbext-eth repo, not the actual HDL one. I need to figure out the proper way of handing ordered sets, as they're not data and it doesn't really make sense to handle them as such, at least in terms of local fault and remote fault.