boot call procedure: New World ROM


Subject: boot call procedure: New World ROM
From: perry phillips (pm_perry@pacbell.net)
Date: Sun Jul 22 2001 - 14:02:07 MDT


Thanks Tim!

This out to be on the Terra Soft website if not in the documentation,
particularly given the problematic nature of multiple boot systems
which many of us are trying to set up. I was starting to get a crude
idea of this by reading the entire ybin program and various technical
notes on OF. YDL is a world all its own and desperately needs
overview documentation like this.
Thanks also for your clear notes on adding "brokenosx" to yaboot.conf
for multiple boot including OS X!

regards,
perry

>
>
>>Still hoping someone will give a crude overview of the order of boot call
>>procedures...
>
>The basics:
>
>Step #1: Open Firmware initializes hardware.
>
>Step #2: OF looks at the "boot-device" OF environment variable
>(which is kept in nonvolatile memory so it's remembered across power
>cycles) to figure out where it should look for something to boot.
>
>Step #3: OF attempts to load whatever "boot-device" points at. If
>it succeeds, it transfers control to the code that was loaded. If
>it fails, it goes through some fallback routines which try to scan
>for MacOS ROM files and the like.
>
>
>When ybin sets up a bootstrap partition, it creates an Open Firmware
>script named ofboot.b in the partition's root directory. This
>script is what provides the textual boot menu, and is a suitable
>target for OF to load in steps 2 and 3.
>
>So, when you type
>
> setenv boot-device hd:XX,ofboot.b
>
>you are simply telling Open Firmware where to find ofboot.b. "hd"
>is an Open Firmware alias that Apple puts into all their OF
>environments; it points to the master device on the primary ATA bus.
>"XX" is the partition number to look at on "hd". The characters
>after the comma are what file to load from the specified drive and
>partition. The comma and colon are simply separator characters.
>
>So -- the failures when using "ofboot,b" are simply because OF can't
>find any file with that name.
>
>The only other way to get ofboot.b to load is something similar to this:
>
> hd:,\\:tbxi
>
>This is a special code which tells Open Firmware to scan each
>partition of "hd" for a file with the Macintosh creator code "tbxi",
>and load the first one it finds. Usually such files are Classic
>MacOS ROM files, but ybin creates ofboot.b with the creator code
>tbxi so it can be recognized by this scanning routine.
>
> Tim Seufert

-- 



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