Re: Superdrive Controllers $59

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

<pubpc1@library.ucla.edu> wrote:

> David Empson wrote,
> in response to my reply:
> > > The fact that GS/OS can't boot without the ProDOS
> > > FST demonstrates this same levelness.
> > 
> > Was there a typo in that last sentence?  GS/OS _can_ boot without the
> > ProDOS FST, but only if booted from an AppleShare server.
> 
> You caught my mistake.  :)
> 
> My point was that in order to boot from a ProDOS formatted
> volume, GS/OS needs the ProDOS FST.

Ah, that makes more sense.

> I was pointing out that this illustrates GS/OS has no default
> filesystem.  It communicates with ProDOS on the same level as HFS,
> AppleShare, and ISO-9660.  Namely, through FST's.

Yes indeed.

The main reason that it is not possible to boot GS/OS from an HFS volume
is that block 0 of an HFS disk contains data in the first few bytes,
where the boot code would need to reside to be supported by the
firmware.

The easiest way GS/OS could have been made to boot via HFS would be to
update the firmware in all affected ROMs (motherboard ROM for the 3.5"
drive, all SCSI cards, the SuperDrive card, etc.) so that they recognise
an HFS volume and adjust the boot procedure slightly.  It would also
require a device which has SmartPort firmware (which rules out the
RamFast, at least the last version I looked at).

Another option would be to modify just the motherboard firmware so that
the boot sequence made use of the SmartPort driver to pre-read the boot
block and use alternative code if an HFS volume is detected.  This
wouldn't cope with a direct jump to $Cn00, however.

GS/OS would also require a new stub OS loader, the equivalent of the
PRODOS file in the root directory.  This would load the main components
of GS/OS and tell the OS that HFS is the boot FST, which would take over
for subsequent file loading.  In theory, this part could be in ROM, but
that might tie the system down to the OS too much.

AppleShare already goes through a different boot mechanism, so it
doesn't have this problem.  All the relevant boot code is supplied by
the server.

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