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

From: D. Peschel <dpeschel_at_u.washington.edu>
Date: Sun Nov 1 19:54:38 1998

> OK, off the top of my head :
>
> Later PETs (the earliest ROMs had diagnostics instead)
> Tatung Einstein (A reasonable Z-80 monitor in ROM, including disk sector
> read/write).
> Science of Cambridge MK14
> All the Intel SDKs (I would think - certainly the SDK-85 does)
> Intellec MCS8i (both a real frontpanel _and_ a ROM monitor...)
> Intel MDS800
> PDP11/03, 11/23, 11/73, etc.
> SGS Nanocomputer
> Heathkit H8, H88, H89, etc (and a lot of other Heath/Zenith systems)
> HP-48SX (not the GX, alas). There's a little hex editor in the ROM which
> you get to by an undocumented key combination.
> Sage II (and I assume Sage IV)
> MPF-88 (and I assume other MicroProfessors)

The Memorex-Telex MTX-500 series has a (very?) good debugger in ROM. I think
the debugger has its own chunk of RAM in a separate address space too. Do
any of the other examples have this?

One of the examples you mentioned is unfortunately not useful to the hobbyist
user (even if the user has experience). The HP-48S and SX hex editor is only
a gimmick without a very detailed description of the internal structures of
the system. (And being in a FORTH-like language on a 4-bit processor, the
internal structures are _vital_. There are lots of magic addresses at other
special addresses in memory. The 4-bit architecture is *little-endian* so
you have to reverse each hex digit of the addresses too.) It's not very easy
to use even if you do have that information.

Besides, the editor is a pain to use. A raw dump of nibbles, only a line of
them, with no address or context information, and an *invisible* cursor?
Realistically I think it was designed for factory testing.

Other examples may fit in the same category. Many Macintoshes have a debugger
in ROM which is so low-level that it's a step back from the Apple ][ monitor
in functionality. Fortunately Apple made up for that by acquiring MACSBUG
from Motorola and adding Mac-specific features. MACSBUG is so powerful that
you can do _interesting_ things like removing copy protection (but you still
need to be pretty expert on the Mac). It's free from Apple. Unfortunately
it's not in ROM.

I'm really hijacking the topic to ask about _useful_ debuggers. Allison
thinks debuggers are a thing of the past. I disagree -- I think they can be
very useful even on a cutting-edge system. Or perhaps my ideal useful debugger
can be very useful on my ideal cutting-edge system. :) Unfortunately their
usefulness depends on the software they're debugging. Perhaps Allison was
making her point because Windows is such a mess and is so undocumented.

Of course writing a useful debugger was difficult in 1980 and is even more
difficult now. (No, I don't know how. No, I'm not sure what's required for
a debugger to be useful.)

-- Derek
Received on Sun Nov 01 1998 - 19:54:38 GMT