1 Mar
2008
1 Mar
'08
10:25 p.m.
On Sunday 02 March 2008 00:44, Vincent Slyngstad wrote:
I think of blinkenlights as way ahead of a ROM with a
debugger in it,
and not for just the aesthetic reasons folks are talking about. It's
a little like Tony's fondness for "things he can understand". When I
use a front panel, there's no question what's going on in the hardware
or what's in the register. The front panel is such a simple device
there is no way for it to lie to me. No way is it going to miss my
breakpoint and wander into the weeds, etc. I'm not acting through
an intermediary -- I really am in control of the machine, and I'm
seeing the real machine state.
I think that's a pretty good point, there.
Later, this got stretched a bit. The actual workings
of an IMSAI
front panel leave some potential for strange things to happen, as
what going on there is a little like a debugger activated by switches.
At least you can really stop the machine, etc.
Which aspects of the IMSAI are you referring to here? The one I have does not
have the original CPU board in it, and the front panel functions are
seriously limited, as in most of it doesn't do much of anything.
Some of the 7-segment front panels with the
microprocessor in them
The Heath H-8 comes to mind.
are stretching the point, too. There's a lot that
can go wonky in those,
that will make it look like things are going on in the CPU that aren't.
Good point. Though that H8 only displayed things in octal, and I always
preferred hex. Otherwise you get into silly nonsense like split octal or
whatever. Too bad it wasn't as easy to get hex displays back when.
But the classic wall-of-switches and lights was wired
into the machine
directly, and couldn't lie to you if it wanted to (except for the occasional
burned out incandescent bulb :-)).
I can see where bi-color LEDs might come in handy here. :-)
One of my first attempts at a logic probe, which I may still have someplace,
was a bit of stuff on perfboard, where two transistors drove two LEDs so
that with the input grounded or open the red one would be lit, and with +5
the green one, so by looking at what you had you could see the level pretty
good. One more circuit detecting transitions and stretching the pulses (the
yellow one of course :-) completed that half of things. I don't think the
tricolor stuff that's out there now was available back when I built that.
I do use debuggers in core, of course, but I percieve
that as a
trade of ease-of-use vs knowing what's really going on.
It all depends on what you're trying to do. Get hardware working at all? Or
something just a bit beyond that...
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin