ROM debuggers (was Re: PDP-11/44 boot prompt)

From: D. Peschel <dpeschel_at_u.washington.edu>
Date: Sun Nov 1 21:06:59 1998

> "Max Eskin" <maxeskin_at_hotmail.com> wrote:
> > I mentioned that all Apple computers have debuggers/monitors.
>
> I wrote:
> > That's certainly not true.
>
> "D. Peschel" <dpeschel_at_u.washington.edu> wrote:
> > You need to substantiate your claim.

> Why is my claim (some X don't have Y) more in need of substantiation than a
> "universal" claim (all X have Y)?

1. Combination and degree. If one person claims that all X have Y, and then
you claim that not all X have Y (= no X have Y (which we agree is false in
this case) or some X don't have Y (which is in dispute)) immediately afterward
without giving evidence, that doesn't have the same effect as making your
claim first. Also, your claim is totally opposite from the previous claim
(that's what I meant by "degree"). So if you want me to believe you, sub-
stantiation is nice. Also, you wrote "certainly". That just makes a naked
claim even less appealing to me.

2. Prejudice. I read your argument and wanted to counter it right away.
("Hmph! Is he thinking that old Macs don't have ROM debuggers? That's not
true in my experience. Is he thinking that new Macs don't have ROM debuggers?
That's also not true -- I *know* the iMac has Open Firmware, for example.")

3. Proving your claim. Unless you've disassembled the ROMs, you don't *know*
there isn't a debugger in there. If I claim there *is*, I may be able to show
it to you easily.

> > Which Apple computers don't have ROM debuggers or monitors?
>
> Did you even spend 30 seconds thinking about the question before you gave
> up and asked me?

Yes. I asked you because of reason 4: I think you're at least partially
wrong.

> There have been many; they outnumber the models that *DO* have a ROM debugger.

This I doubt. You could be right (especially in the case of the Performas)
which I will admit if it's true.

> The ones that fall within the charter of this group (introduced before
> November 1, 1988) are:
>
> Macintosh
> Macintosh 512K
> Macintosh 512Ke
> Macintosh 512K/800
> Macintosh Plus
> Macintosh SE
> Macintosh SE/FDHD
> Macintosh II
> Macintosh IIx
> Macintosh IIcx (maybe, not sure of exact intro date)

No. Many of the older models had a plastic switch that snapped into the
ventilation slots; it would reset the machine or bring up a debugger. I
vaguely remember using the SE's debugger to look at a picture of the
development team that was hidden in ROM.

And as it turns out, Apple has a Tech Note (#1136) on the subject.
(I vaguely remembered it before reading your post; afterward I went and looked
it up. So I'm not trying to be *too* unkind or to have all the evidence
beforehand and bait you.) It says:

About MicroBug

   MicroBug was first introduced with the Mac Plus and has been a
   standard component in the ROM of all Mac OS computers since then.
   MicroBug is invoked when the system takes a Non-Maskable Interrupt
   (NMI) and there is no other debugger (e.g., MacsBug) installed.

   MicroBug is not present on the Macintosh 128, Macintosh 512, and
   Macintosh XL computers.

So you're right about the 128, 512, and XL, but wrong about the Plus, SE, II,
IIx, and IIcx.

I just saw the debugger on my 7100/66 the other day when I hit Cmd-Shift-Power
instead of Cmd-Ctrl-Power. I doubt it's been updated to handle the PPC.
I know many newer machines have Open Firmware (hold down Cmd-Opt-O-F when
turning on -- the letter O, not zero) which could be used for debugging, if
you're evil and know FORTH. :)

I'm not going to reboot my machine while I'm writing this message! So I could
be wrong but I doubt it.

-- Derek
Received on Sun Nov 01 1998 - 21:06:59 GMT