Atari emulators crash with USR function

[Robert S64]

Greetings everyone. I have a little problem with 3 emulators. (I hope this is the right forum). I searched everywhere to find a solution (or lack thereof)

 

When using 3 emulators, (Atari800win Plus 4.0, XFormer and don't know the name of the third. It's an older DOS one) I try to use a USR(X) routine, they all crash.

 

I thought I may have missed something with my code but it was very simplistic so I did a simple...

 

POKE 1536,96 (RTS)

A=USR(1536)

 

Crash

 

It happens with all ROMS. OSA, OSB, XL/XE

 

Anyone know of a resolution for this?

[GroovyBee]

You might find this useful :-

 

http://www.atariarchives.org/roots/chapter_8.php

 

You need a PLA before the RTS to "clear the stack"

[Robert S64]

Ahhhh. Thank you thank you very much. When I added one PLA it still crashed. Then it started all coming back to me. There is a 3 byte stack.

 

Thanks a ton

[Rybags]

1st stack entry, always has to be pulled = number of parameters, 00 = none e.g. USR(routine)

 

e.g. 01 - 1 parameter, like USR(routine,parm1)

 

Each parameter if supplied is another 2 bytes you have to pull. High byte comes off first, then low each time.

Edited July 2, 2011 by Rybags