11 Sep
2002
11 Sep
'02
4:25 p.m.
The Imlac CPU has a special instruction that generates a TTL signal to
trigger a scope for
debugging, a special 'scope loop' opcode. I'd never seen this before
the Imlac, its been very
handy too!
Tony Duell wrote:
I've never
heard of a scope loop. What is it?
A tight software (or maybe even microcode) loop that keeps on doing the
same thing to a particular section of the circuitry. You thus get
repetitive signals that you can look at on an old-fashioned non-storage
oscilloscope.
Before most serious repairers had logic analysers, such loops were often
the only way to observe how parts of the machine behaved at full speed.
Many diagnostic routines included them (I have certainly seen them
mentioned in MAINDEC listings, for example).
-tony