DEC840: No serial output from BIOS, how to reset?

[feld]

How can I reset the BIOS when there is no serial console output until the Opnsense/FreeBSD kernel loads? I believe this may be due to disabling the Legacy UART to get serial console working again.

If anyone else is reading this, what you probably need to do on this specific hardware is leave the BIOS alone and change the Serial Console to EFI in OpnSense.

[feld]

I got this working again but I'm not sure it was due to my actions.

I pulled the firewall from service and was going to open the chassis when I noticed there was a tiny pinhole on the front that I've never seen before. I pushed the button in the pinhole which I hope cleared CMOS, then did a clean power cycle and I was able to see the serial console again.

I could not find hardware documentation for the DEC840 that indicates exactly what this button is for.