Recovering from dead NVRAM on a sun4m

These instructions are here as a memory aid for me, and are used to recover from a dead NVRAM in a sun4m system (tested on Sun SPARCstation 4/5/10/20, and SPARCclassic). First, pick numbers XX, YY, and ZZ, each of which are valid two-digit hex values, and where the MAC address 8:0:20:XX:YY:ZZ is unique on your network.

Any line with a leading # should be treated as a comment and NOT TYPED. At the OpenBoot PROM prompt, enter:

set-defaults
setenv diag-switch? false
# Next command optional and tells system not to test all
# memory every reset. It may be the default on your system.
setenv selftest-#megs 1
# Next command invalidates NVRAM checksum
# so following mkpl command works
f idprom@ 1 xor f mkp
8 0 20 XX YY ZZ XXYYZZ mkpl
# After hitting enter on previous command, there is no prompt.
# Now type Ctrl-D Ctrl-R, and 'ok' prompt should appear.

Now you can reset the system (without disconnecting power!) and it will come up with the MAC address 8:0:20:XX:YY:ZZ.

Note: I couldn't find a clean way to set the NVRAM clock from the OBP prompt, meaning that on first boot, your OS will have a wacky time set.