Post by thread:[OT] HALT instruction Skip always IS useful

'[OT] HALT instruction Skip always IS useful'

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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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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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.rolfTakeThisOuTualberta.ca> wrote:

{Quote hidden}> 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.

> 

> _______________________________________________

> http://www.piclist.com

> View/change your membership options at

> http://mailman.mit.edu/mailman/listinfo/piclist

>

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