Re: Making an HFS parition boot (6.0.1)

[dempson@actrix.gen.nz (David Empson)]

Supertimer <supertimer@aol.com> wrote:

> m.kelsey@spam.eecs.wsu.edu wrote:
> 
> >What's the trick to getting a GS/OS HFS partition to boot?  I copied
> >the files from a ProDOS 8 volume onto an HFS partition but my RAMfast
> >isn't able to boot.  It just sits there.
> 
> You can't get GS/OS to boot from HFS.
> 
> According to a post by David Empson, GS/OS uses code in the
> boot file "ProDOS" in the root directory of a GS/OS boot volume
> to access the ProDOS file system and load the essential files
> before hitting the FSTs.  Then it loads the ProDOS FST and uses
> that.

Actually, that is only ONE of the problems.

The major problem is that there is no way to put boot code for an Apple
II on an HFS volume, since the HFS format defines the fields at the
start of block 0 as containing information about the volume.

Speaking hypothetically now...

There are several requirements for being able to boot an HFS volume on
the IIgs:

1. An upgrade to the IIgs system firmware so that it recognised an HFS
volume and booted specially, e.g. by using the SmartPort driver to read
block 0, check for HFS, and if identified use a special boot operation,
otherwise jump to the standard boot code for that card (which would load
block 0 at $0800, check that $0800=$01, then jump to $0801 as normal).

Interesting point: the RamFast SCSI card didn't have a SmartPort driver
last time I looked (version 2.x).  If this hasn't changed, then a
generic HFS boot mechanism provided by the system firmware would not
support a RamFast (though the RamFast could implement this itself as
part of its standard boot code).

It would work with an Apple 3.5 Drive, UniDisk 3.5 or SuperDrive on the
IIgs disk port, or with a SuperDrive card, or with an Apple SCSI card
(either type), or a "slinky" memory expansion card.  (Any other
SmartPort devices out there?)

Any such firmware would need to contain a mostly complete read-only
implementation of HFS.  (The Mac can do this because the File Manager,
which implements HFS, is in ROM.  The IIgs has no file system
implementation in ROM, only the barest support for bootstrap loading an
arbitrary operating system.)

2. An HFS-specific version of the GS/OS boot loader (equivalent of the
PRODOS file).

Now that I think about it, having the minimal HFS support in ROM as
described above would completely remove the need for this file, as long
as booting an HFS disk was always going to take you into GS/OS.  The ROM
could simply copy a stub of itself into bank 0 and load START.GS.OS
directly.  START.GS.OS depends on the code provided by the GS/OS boot
loader until the boot FST and device driver have been loaded.

3. A standard for how GS/OS system files are arranged on an HFS volume.
Presumably this would match a ProDOS volume for simplicity, and as long
as the IIgs system folder was called "System", there wouldn't be a
conflict - the disk could boot either a Macintosh or IIgs as long as
both systems were present.


It would be an amusing exercise to write an application that supported
all this.  It could run under DOS 3.3 on a 5.25" disk for example.

Hey - the Apple III returns: must pre-boot from a 5.25" disk!  :-)

Now there's a thought: I wonder how much free space there is in the ROM
of the RamFast and Apple High-Speed SCSI cards?

(Don't mind me - I'm only rambling...)

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand