[Simh] On {O,D}DDT

[Timothe Litt]

On 21-Jan-16 11:53, Paul Koning wrote:
>> On Jan 21, 2016, at 10:58 AM, Ethan Dicks <ethan.dicks at gmail.com> wrote:
>>
>> On Wed, Jan 20, 2016 at 8:37 PM, Johnny Billquist <bqt at softjar.se> wrote:
>>> ODT actually stands for On-line Debugging Tool, not Online Debugging
>>> Technique.
>> I recall Octal Debugging Technique.  Anyone else remember that definition?
> Things get interesting...
>
> The name ODT was derived from the TOPS-10 debugger DDT -- an obvious name in that era for something that gets rid of bugs, but officially it stood for "Dynamic Debugging Technique".
>
> ODT was much simpler, not offering symbolic debugging for one thing.  So it got a different name, and since its I/O was pretty much just octal numbers, replacing "dynamic" by "octal" made sense.
>
> Then again, the DOS V9 manual says it's "On-line debugging technique".  So do several RT11 manuals.  Hm.  Now I'm puzzled.  I clearly remember "octal" and don't remember ever seeing "on-line".  And sure enough, the header of the source code for RSTS "monitor ODT" (the kernel debugger) says "Octal debugging tool".
>
> So it looks like DEC wasn't consistent.  On-line in some places, octal in others, and "technique" in the official documents I remember but "tool" at least internally (a more obvious word to use, certainly).
>
> 	paul
>
>
Besides multiple technical writers, editors and product managers: there
were multiple implementations - including some for non-DEC machines.  I
had a small part in DDT-11, and also implemented an ODT-clone on 8 and
16-bit uPs.  ODT was, IIRC originally called Octal Debugging Technique,
in a nod to DDT.    Actually, there are two DDT-11s; one that runs on
the -11 (used in ANF-10 network nodes), and one that lives on a -10 (or
-20) and remotely debugs the -11, and/or the 11's crash dumps.  In fact,
DDT-11 can be booted in exec mode on a KS10, and run PDP-11 diagnostics
under simulation against real hardware.  (Yes, I did that.)

Of course, DDT was also an octal debugger (unless you changed the input
or output radix) - and more capabie as it could deal with symbol tables,
paging, and so forth.  But ODT was *only* capable of debugging in
octal.  (A consequence of the PDP-11's 4KW minimal and 28K maximum
memory size.)  So that's what it was called.  Someone in marketing
decided that octal was too geeky, and that 'on-line' would sell better. 

Engineers being what we are (many students of human, as well as computer
languages), pointed out that "technique" is how one uses a tool.  But
it's a stretch to call a tool a technique, at least in ordinary usage. 
So 'tool' was floated, but by that time ran against the couple of
decades of established culture.  (A very long time in technology-years.)

An early DDT manual (~ 1970, but I've lost the colophon page) explains
the DDT situation thusly:

INTRODUCTION
DDT-10 (for Dynamic Debugging Technique) * .... long page

In very small print, smaller than I can reproduce here:
*Historical footnote: DDT was developed at MIT for the PDP-1 computer in
1961.  At that time DDT stood for "DEC Debugging Tape".  Since then, the
idea of an on-line debugging program has propagated thoroughout the
computer industry.  DDT programs are now available for all DEC
computers.  Since media other than tape are now frequently used, the
more descriptive name "Dynamic Debugging Technique" has been adopted,
retaining the DDT acronym.  Confusion between DDT-10 and another
well-known pesticide, dichloro-diphenyl-trichloroethane (C_14 H_9 Cl_5 )
should be minimal since each attacks a different, and apparently
mutually exclusie, class of bugs.

Oddly enough, this paragraph subsequently caught the attention of folks
who had power, but not much humor.  So it was removed.  But it stuck
with me, and is one of the few chemical formulae that I always have
instantly to hand.

We also had *DDT products for various high-level languages, among them
ALGDDT (Algol), PASDDT (Pascal), COBDDT (COBOL), FORDDT (FORTRAN) and
SIMDDT (SIMULA).  But none retained the marvelously efficient, if not
obvious at first glance, command syntax.  They all used DCL-like syntax,
though they were long before that standardization effort: "examine",
"break", etc.  I still think '/' is the obvious way to examine a
variable... and $B to set a breakpoint.  My  fingers still rebel at
verbose commands and carriage-returns when debugging on 'modern' machinery.

The other somewhat amusing thing is that DDT's adoption of the <ESC>
(echoed as '$') key required a lot of explanation in the manuals, as
various models of Teletype^TM caused keys located in the upper left
corner of their keyboard to emit different codes -- or the same codes,
with different labels.  The monitor had SET TTY commands to map these
down to <033>.

And that's more than you wanted to know...probably.





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