POP for clearing GOSUBs off stack

[Pinacolada]

I know it's ugly, but I'm working on a program in BASIC where I need to POP the last GOSUB off the stack. I've tried kludges like setting flags to designate GOTO vs RETURN, but I think POP would be better.

I've tried Googling comp.sys.cbm, no luck.

Assembly preferred, mainly so I can study and learn?

Edit: I know where the stack is, there is a value which says "Here is a GOSUB" and four more bytes after that. My assumption is that you would PLA stuff from the stack including and after that byte.

Is there a stack depth byte which needs to be decremented, too?

Edit: TSX and TXS opcodes exist, okay, hmm...

[Pinacolada]

Got this answered by xlar54. Thanks.

[Robin Harbron]

Nov 19, 2008 19:00:43 GMT -5 Pinacolada said:

Got this answered by xlar54. Thanks.

Can you share with us here? I looked into this briefly, but couldn't find a good answer. I wasn't sure if there was more to it than just clearing the info off the 6502's stack (like, if BASIC kept other related info elsewhere).

[Pinacolada]

Here is the disassembly. Can't tell you much about it, don't understand a whole lot. I'll try to study later.

.C:02a7   68         PLA
.C:02a8   68         PLA
.C:02a9   A9 FF      LDA #$FF
.C:02ab   85 4A      STA $4A
.C:02ad   20 8A A3   JSR $A38A
.C:02b0   9A         TXS
.C:02b1   C9       CMP #$
.C:02b3   F0 03      BEQ $02B8
.C:02b5   4C E0 A8   JMP $A8E0
.C:02b8   68         PLA
.C:02b9   68         PLA
.C:02ba   68         PLA
.C:02bb   68         PLA
.C:02bc   68         PLA
.C:02bd   60         RTS