"7i92+7i76 on P2: SSerial detects board but registration fails with EAGAIN"

Found it — the 5V logic supply was sagging to ~4.08V under load (was running off a 2A phone charger feeding both the 7I92 and 7I76 through the cable). Swapped to a proper 5V/7A supply, and GPIO pins now show a clean, full swing (5.09V/0V) where they were previously stuck flat regardless of software commands.Credit to tommylight and PCW — you both flagged marginal 5V power as a suspect early on, and that's exactly what this turned out to be.

Going to retest the SSerial/x2D setup with solid power now — will report back on whether that resolves the EAGAIN registration failure too.

Thanks both for the help.

You guys rock!

Confirmed — the weak 5V supply was the entire problem. With a proper 5V/7A supply in place, the exact same x2D bitfile that failed with EAGAIN yesterday now registers cleanly and shows full SSerial field I/O (input-00 through input-31, output-00 through output-15, spindle pins, all live). Thanks again for pointing at power — solved it completely.

Final update: fully resolved. Turned out to be two separate issues layered on top of each other — the weak 5V supply (confirmed earlier), plus a ribbon cable causing intermittent SmartSerial comms errors (Timeout/Extra character/Serial Break, escalating to port shutdown after ~6 minutes of runtime). Replaced the ribbon cable with a direct DB25-to-DB25 connection between the 7I92 and 7I76 (board mounted directly on the 7I92's P2 socket) — 30+ minutes stable, zero faults. E-stop wired to TB6-1/input-00 and confirmed working through PathPilot's UI.

It's worth noting, the ribbon cable fault was probably the proximity of a switching power supply nearby with everything laying on a table.

Thanks again to all for the help throughout.