Has anyone run into PCIe x16 link issues when using it as x1?
I have several of these ASUS M4A79XTD
boards and just begun populating them with more than 2 ATI cards each and have run into an interesting issue.
I can successfully run 3 5770's in these boards, 1 in each of the actual x16 slots (onboard) and 1 via an x1 slot/extender (offboard). No problems here.
When I lift the same 5770s offboard and connect 2 of them to the same x16 slots via x1 extenders I lose the second x16 slot entirely. The first x16 slot closest to CPU functions just fine using an x1 extender however the second slot is dead. Nothing in lspci for that slot/card. As expected, dropping 1 5770 back into the second x16 slot and connecting another 5770 via an x1 extender to the first x16 slot works just fine.
I noted in the specs on these Asus boards that 2 GPUs in the x16 slots drop them both to x8 but I doubt that is related unless it is forced x8 link. I have tried several (4) different x1 extenders, all exhibit the same behavior.
I have some x16 extenders on the way which I suspect will resolve the issue but I am curious if anyone else has run into anything similar. Am I missing something obvious?