Re: Where does the "16 SECTOR" message come from?

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

Tristan Mumford <xtristan.xmumford@xgmail.xcom> wrote:

> David Empson wrote:
> 
> > Tristan Mumford <xtristan.xmumford@xgmail.xcom> wrote:
> > 
> >> It's probably a blatantly stupid question to most but before today I have
> >> never seen the "16 SECTOR" or "13 SECTOR" boot messages. Where is it
> >> stored? Is it in the diskII ROM or AppleSoft?
> >> 
> >> Sorry for the question, but I can't find where it lives.
> > 
> > Neither of the above.
> > 
> > The Disk ][ controller firmware contains no displayed text at all.
> > 
> > Applesoft predates any disk operating system so it knows nothing about
> > sectors.
> 
> Thought as much about AppleSoft. But this left me doubtful. I have barely
> ever used the controller that generated this message. It was in the
> currently "sleeping" clone ][. it's now in my //e for the purpose of
> testing my 3.5" adaptor.

There's a clue: you have a third-party disk controller? It might contain
additional code which attempts to identify the disk as being 13 sector
or 16 sector, and then boots accordingly.

> > I'm not aware of anything which would display messages saying "16
> > SECTOR" or "13 SECTOR" other than specific code loaded from disk,
> > perhaps the "BASICS" disk which lets you boot a 13 sector disk on a 16
> > sector controller.
> 
> That is truly interesting. Before my head-stepping microcontroller packed up
> on me (working on building an adaptor to use one of my bigger ones) I had a
> few failed attempts at prodos formatting and copying ProDOS to that disk,
> which failed every time because of an error in my uC head stepping code.
> 
> So unless ProDOS has those messages on track 0 which would genuinely
> surprise me

Definitely not. ProDOS wouldn't deign to lower itself to deal with 13
sector disks. Way too passe.

> or this funny clone controller can boot 13 and 16 sector disks, and
> perhaps alert people to a nonbootable disk of a particular type.
> because it displayed "13 SECTOR" and "16 SECTOR" messages very neatly in
> the dead centre of the screen.

That is very likely. I've never seen anything resembling these messages
from any standard Apple software, firmware or hardware.

> > On a standard DOS 3.3 system master (late edition) the only code with
> > support for 13 sector disks is the MUFFIN and BOOT13 programs.
> > Everything else (including DOS 3.3 itself) expects 16 sectors.
> >
> 
> Now I'm really curious. I think I have a dos 3.2 disk somewhere that I can
> test 13 sector with, after I give one of the clone 5.25" drives a good
> clean that is.
> 
> I like a nice little mystery. What gets me is the ROM would have to support
> the normal Disk ][ stuff along with fitting at least "SECTOR" in there too
> and a means of detecting and displaying the message. Now I'm really
> curious.

Me too. It might use bank switching to change the firmware image in the
$Cn00-$CnFF area: the initial code would check the disk format, then it
switches in either the standard 13-sector or 16-sector firmware, so it
should be compatible with code which depends on the standard firmware
(e.g. copying it into RAM and patching it).

The 13/16 sector detection code would only work at boot time, but the
only way I can think of it detecting a boot would be if it was a
power-on reset. Any other method would result in the detection code
appearing, or would require slightly nonstandard firmware to at least
branch out to some extended firmware to do the detection (e.g. in the
$C800 space).

-- 
David Empson
dempson@actrix.gen.nz