Use production DCB with Pathfinder

Production DCBs have an additional input to the master GBTx reset (BP_MC_EC_RESETB) coming from pin H43 on the backplane connector. This pin is grounded in the Pathfinder, and since the RESETB is active low, the DCB was in continuous reset.

We fixed this issue by providing 3V through the manual reset MAN_MC_EC_RESETB, which comes out to the FFC breakout board connected to the optical mezzanine. As shown in the circuit below, the 3 V is divided to 1.5 V at the GBTx input and the DCB worked fine.

Here's a schematic on how a 3 V pull-up would work:

Here's the actual modification needed on the FFC breakout board: