Date   : Wed, 25 Nov 2009 02:24:39 +0100
From   : rick@... (Rick Murray)
Subject: Quine

Mick Champion wrote:

> Oh right. So you couldn't PLA from within a subroutine when you had 
> PHA'd from the outside it,  unless you pulled it twice amd remembered to 
> push the 1st byte back?

Messing with the stack out-of-sequence can be useful if you are writing 
a custom interrupt handler with dispatching. It can be easier to toss 
stuff off the stack and RTI than to go through a chain of RTSing. 
However it is Hairy (with a capital H). If you're writing your own OS, 
go for it. If you're writing your own single-tasking highly-specific 
program, go for it. If you plan to co-exist with anything else (this 
includes the factory-fitted MOS), you'd better not...


> TSX // take RTS address out of the stack

^ Addresses are 16 bit, remember.

And, um... don't have my booklet to hand, but doesn't TSX copy the stack 
POINTER to X, not actually pull anything?


> Never touched the stack.

Stack's good. Needs discipline though.


Best wishes,

Rick.

-- 
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...
 >> TO PRIVATE MAIL ME, REMOVE [BBC-Micro] FROM SUBJECT <<