Tips and Tricks For The PROM

SPARC-based computer systems use what's called the PROM to control hardware,
boot the system, and run diagnostics.  The PROM is actually the memory chip
and it stores the firmware that the system executes.  The software that runs
is called OpenBoot.

The system boots, loads the firmware, and executes it.  The firmware is then
responsible for making sure all the hardware works, loading a single program
into memory, and running it.  Most often, this single program is an operating
system.  But it doesn't have to be.

OpenBoot may look alien to you if you have a lot of experience with Intel
hardware.  But rest assured, after a few days of entering commands at the
"ok" prompt, you'll feel at home in no time.


SUMMARY

   Like I mentioned, OpenBoot is the software on the PROM chip that the
   system loads and executes each time you turn on the system.  OpenBoot
   is built around the Forth interpreted programming language, so anything
   you want to add to it can be written in Forth.

   To access OpenBoot, hit STOP+A (or L1+A) on your keyboard.  If the system
   is just starting up, you will be presenting with an "ok" prompt.  If the
   system is currently running that single program, you will see something
   like this:

      Type b (boot), c (continued), or n (new command mode)
      >

   Hit "n" at that prompt and you'll get an "ok" prompt.

   Congratulations, you're now at the OpenBoot console!


BASIC COMMANDS

   The obvious first command would be "help", which displays a list of
   available commands.  You can in turn type "help <command>" for help on
   that specific command.  The most useful commands are described below:

   printenv
      Displays the current system settings.

   setenv
      Used to change a system setting.

   reset
      Restart the system.

   boot
      Boot the system.

   You should have a look at each of the help screens for those commands.
   In fact, play around with each of those to become comfortable using them.
   If you render the system settings completely useless, you can enter the
   OpenBoot console and type "set-defaults" to restore factory defaults.
   Of course, if you go and set a password and then forget it, you have no
   way of recovering that except to buy a new NVRAM chip from Sun.  :^)


DEVICES

   All of the system devices are represented in the device tree.  This is
   a virtual thing that is layed out like a filesystem.  To start, type
   "show-devs".  You will see a listing of the devices on the system.  You
   can type "cd" and "ls" on these nodes just like you would on directories
   and files on a real filesystem.  Typing ".attributes" in a directory
   will show you the values for the current node.

   You'll soon find that device paths in the device tree are incredibly
   long.  So long, that you'll want shorter names to represent common 
   devices.  The "devalias" command can help there.  The syntax is:

      devalias <alias> <device node>

   You can alias a node to something like "harddisk".  Or something similar.
   Keep in mind that the devalias command will not retain the device aliases
   after a system reset.  Therefore, you should probably use the "nvalias"
   command to set the alias so it stores it to the nvramrc.  This file is
   sourced by OpenBoot when you enter the console.  The syntax is the same
   as the devalias command.  To undo an nvalias, use "nvunalias".

   Diagnostics are always impressive.  And OpenBoot offers several tools for
   checking the system.

   test <device node>
      Test a specific device.

   test-all
      Test all devices.

   probe-scsi
      Search for onboard, Sun SCSI controllers and devices.

   probe-scsi-all
      Search for any and all SCSI devices in the system, even third party ones.

   watch-clock
      Test the clock.

   watch-net
      Monitor network traffic.

   show-sbus
      Search for any SBus adapters.


COOL STUFF

   I like to setup nvaliases for my Slackware and Solaris partitions so that
   I can easily type "boot linux" or "boot solaris" at the ok prompt.  Using
   the nvalias command, you can set up these aliases.  Don't forget to run
   "setenv use-nvramrc? true" so that the nvramrc file will be sourced when
   you boot the machine.

   And I also like to replace my default boot logo with the Slackware
   "underbar S" logo.  The http://www.ccl.kuleuven.ac.be/~bob/oem-logo.html
   page can help you with that.  :^)


Enjoy!

--
David Cantrell
david@slackware.com