Found on Sunsolve (realize things like Stop-a may crash your server):


Here are the steps to set up several (TurboGX) tgx cards.

(This may make assumptions about the OpenBoot[TM] prom rev level
and the resolutions the frame buffer supports.)

1) The console monitor is set up using output-device

User can find which device is the console monitor with:

L1-A (Stop-a)
ok devalias screen

It should say something like /sbus@1,f8000000/cgsix@3,0 this is
the console screen. This string will differ on other types of
hardware. For instance, it may be /obio/cgfourteen@2,0 on a
sparc-20.


Next, look at all the frame buffers on the system:

ok show-devs
... /cgsix@0,0
... /cgsix@2,0
... /cgsix@3,0


It has already been seen which device was the console frame buffer.
The other two frame buffers are cgsix@2 and cgsix@3. This output
will widely vary depending on the system architecture.


Now, set up a shell script:


#!/bin/sh
eeprom output-device='screen:r1280x1024x76'
eeprom fcode-debug\?=true
eeprom nvramrc='probe-sbus
" /iommu/sbus/cgsix@2" select-d ev
r1280x1024x76
" /iommu/sbus/cgsix@2" " set-resolution" execute-device-method drop
device-end
" /iommu/sbus/cgsix@3" select-dev
r1280x1024x76
" /iommu/sbus/cgsix@3" " set-resolution" execute-device-method drop
device-end
install-console
banner
'
eepr om use-nvramrc\?=true


Pay attention to the spaces within the double-quotes.

The output-device line sets the resolution for the console, which
is the primary frame buffer.

The nvramrc line sets up code that executes each time the system
boots. This program sets up the resolution on the second and
third tgx devices.

The last line says to use the script in nvramrc when booting.

Notes:

To find built-in resolutions available for some of the newer frame
buffers (this doesn't work for all devices), type:

L1-A
ok show-devices
...
/sbus@1,f8000000/cgsix@3,0 <-- this is the frame buffer
...
ok cd /sbus/cgsix@3,0
ok words

The resolutions supported show up like r1280x1024x76 (or hdtv).

Other references:
Open Boot Command Reference

Writing Fcode Programs