Hmmm, did littel reading in the OpenFirmware manual I linked above. There is an example how to use show-devs for listing the existing devices. The example contains...
/virtual-memory@0,0 /memory@0,0 /counter-timer@1,f3000000 /eeprom@1,f2000000 /openprom So being lucky, the hex numbers given are the physical (non-mapped) address of memory, eeprom and counter-timer (=NVRAM). A check would be using the firmware's read commands to see if there is information starting at f3000000 and more specific whether the locations f3001ff9 - 73001fff show any change (that is the location where the real time clock should appear if there is a NVRAM at this location.
