2 Mar
2008
2 Mar
'08
8:06 a.m.
From: "Chuck Guzis" <cclist at sydex.com>
On 1 Mar 2008 at 21:44, Vincent Slyngstad wrote:
I'm not talking about debugging hardware. I'm not really very good at
that, so wouldn't presume to tell you which tools to use :-).
We always assumed our machines were in good repair, and that the
hardware was essentially perfect. (Our PDP-8's never contradicted
us, either :-).)
What I am saying is that, when debugging software, it is useful to
be really sure about what is happening, an the front panels gave
that reassurance, in a way that debuggers and emulators just don't.
Since debuggers and emulators crash or malfunction, they don't
mimic the underlying hardware perfectly, whereas the front panels
gave visibility into the real thing.
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".
Well, if I were debugging hardware, I'll take a logic analyzer and a
scope, thank you. I'm not sure how broad the range of hardware
faults is that a bunch of blinking LEDs will indicate. I'm not above
using a bus card with indicators and switches on it--but the card
goes as soon as the hardware gets debugged. I earned my stripes in the big-iron days.
Hands-on-dedicated time on
systems was hard to come by. Come in at 2AM or 3AM, in hopes of
getting some work done, hang around for the 9AM status report, go
home, eat supper and go to bed. A worse case happens when the
closest available machine is half across the country--and you have to
catch a flight to check out your system changes. It made me hate
travel something awful.
Sure.
With hurdles like that, you tend to develop a habit of
debugging your
code *away* from the machine. Even when time was available, often
there simply weren't any good tools. Try debugging a CDC 6600 PPU
program. No lights, displays or anything else to help you. If
you're patient and the CEs aren't too nosy (they don't like non-CE
types going behind the skins), you can grab a scope and read the P-
counter of a specific PPU--assuming that your code hasn't trashed its
memory and rendered any postmortem dump you get meaningless.
The fact that you ever had to grap a 'scope and read the P-counter
seems to support my argument for real lights, not refute it :-).
That isn't to say that I've never used a
machine with an elaborate
front panel; I just never found one to be terribly useful in the long
run.
I don't claim they are useful in the long run. They are useful in
certain difficult debug situations, similar to what is done nowdays
with ICE.
Vince