Accessing the Sun PROM on OpenBSD

After installing OpenBSD on my Sun Blade 100, the "stop-a" BREAK sequence no longer provided access to the PROM (which I expected to happen). While running OpenBSD, however, I found that it is impossible to access the PROM (key-words: while running...you can still access it before the OS loads). Using eeprom or openprom allows you to modify various PROM settings while OpenBSD is running, but sometimes you need to get to the actual PROM.

Problem

How to access the Sun PROM when an OS other than Solaris is installed? When I shut down, I can see the PROM command line, but it doesn't accept input?

Solution

Once the OS starts to load, you will be unable to access the PROM like you normally can when running Solaris. You must reboot the system and send a BREAK sequence before the OS starts to load (on a Sun keyboard, this is done via the "stop-a" sequence). You will then have access to the PROM command line.

To make it easier, you could simply set the PROM variable auto-boot? to false so that whenever your system starts up, the OS will not automatically boot and you will be given a PROM command line.

To do this, use eeprom (or openprom if eeprom is not available) and do the following:

   # eeprom auto-boot?=false

If your shell is trying to interpret the '?', just escape it:

   # eeprom auto-boot\?=false