Date: Thu, 2 Feb 1995 18:35:35 -0800
From: stevez@bigboy74.West.Sun.COM (Steve Zucker)
Subject: Item #228: Proposal for change to PowerPC binding

P1275 Openboot Working Group Proposal -- Proposal #:228 Ver 1


Title:          Boot order change for PowerPC

Author:         Steve Zucker

Date:           2 Feb 1995

Ed/Tech:        Technical

Synopsis:       Boot from ISO-9660 directory before checking for partitions

Doc & Version:  All to date

Problem:

	OS vendors (at least SunSoft) will want to provide one CD-ROM
	for both "legacy" firmware and Open Firmware on PowerPC.  One
	nice way to do this is to boot a software implementation of
	Open Firmware on legacy systems.  If the "search order" is the
	same on legacy and Open Firmware implementations, Open Firmware
	would perforce boot the software implementation, which would
	then reboot itself ad infinitum.

	As presently written, the PowerPC supplement to 1275
	("Partition formats" section) specifies that the presence of a
	partition table on the boot medium causes Open Firmware to boot
	from the active or selected partition, even if there is a valid
	ISO-9660 directory on the medium.  This is exactly what the
	legacy firmware does, leading to the inability to simply boot
	a software implementation of Open Firmware.

Proposal:       

	In the "Algorithm locating boot file", move the test for ISO-9660
	to be first, so that with real Open Firmware, the file will be
	located in the ISO-9660 directory, while with legacy code, an Open
	Firmware software implementation can be booted from a bootable
	partition specified in a partition table.

	After the change, the algorithm will read:


	read sector 16.
	if a valid ISO-9660 directory is found
		locate the file, using the ISO-9660 directory
	else
		read sector 0 (bootsector).
		if last 2 bytes of sector are 0AA55h (little-endian)
			if bsMedia == 0F8h ...
			...
			use directory of the selected partition to locate file
		else (non-partitioned)
			use FAT-12/FAT-16 directory to locate file
			

[ P1275 Item #228 -- Received: Thu Feb  2 18:38:59 PST 1995 ]