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'[OT] HALT instruction Skip always IS useful'
2004\10\06@230417 by Robert Rolf

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William Chops Westfield wrote:
> Always, or Never"  "Subtract One and Skip never" was sometimes used to
> decrement memory, but "skip always" was pretty useless...

Skip always is quite useful when debugging. It allows you to
force a skip without changing the instruction size. This is
particularly useful when debugging code in RAM or where
you have very slow data link for uploading code changes.
(DDT on a TTY at 110 baud).

Robert

Wipe out all of memory with ONE instruction. PDP11 family.
Mov -(PC), -(PC)        ;start at highest memory location.

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2004\10\07@000437 by William Chops Westfield

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On Oct 6, 2004, at 8:03 PM, Robert Rolf wrote:

> Skip always is quite useful when debugging. It allows you to
> force a skip without changing the instruction size.

We must be talking about a slightly different processor.  The
one I'm talking about (PDP10) only had one instruction size,
and "skip" wasn't as simple as a bit.  You're talking about
the pdp8?  IIRC it has some instructions with a bunch of modifier
bits that could be set.

Still DDT, though.  that was a nice debugger for those days.

BillW

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2004\10\07@160941 by Ben Hencke

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Skip always? Something like
btfsc PCLH, 7 ;or some other always 0 bit

I think I used something like that to logical NOT a conditional skip
instruction.
ie

incfsz reg, f
skip
bsf  PORTB, bit

So it would set the pin if reg was zero. Saved the trouble of using goto ;-)

- Ben




On Wed, 06 Oct 2004 21:03:55 -0600, Robert Rolf <spam_OUTrobert.rolfTakeThisOuTspamualberta.ca> wrote:
{Quote hidden}

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