jumping out of a gosub reminder

[mpgmike]

Here is a simple exercise to review the Stack:

10:  Main:
20:  DO
30:   IF PORTB.1 = 1 THEN
40:      GOSUB CheckIn
'  Stack Contains 40
50:    ENDIF
60:  LOOP

70:  CheckIn:
80:    IF PORTB.2 = 1 THEN
90:      GOTO Verify
' Stack Still Contains 40
100:  ENDIF
110:  RETURN

120:  Verify:
130:    IF PORTB.1 = 1 THEN
140:      RETURN
'  This RETURN jumps to the address in the Stack + 1 (address), so the point of RETURN = 50
150:    ELSEIF PORTB.2 = 1 THEN
160:      GOTO NameCalling
'  Stack Still Contains 40
170:    ENDIF
180:  RETURN

[longpole001]

thanks mike

i am going though this code slowly to find any goto's that have found their way into sub's , fixed about 10 or so that if the error condition happend wold have acted on the goto , and left the stack with the address sitting on there from the gosub

[mpgmike]

I commonly use GOTO to jump from one Sub to another when there is nothing left to do in the first Sub. This keeps the Stack from building up, and reduces execution time. Working with the Nextion TFT screens, sending UART commands must terminate with $FF $FF $FF, which I often add in a subroutine. Since that is the last part of the operation, I GOTO FfFfFf: from the last part of the Send_Data: routine, then RETURN from FfFfFf:. It saves a couple jumps, which may involve ASM BANKSELs.

Know that you are doing it intentionally, know where your Stack is pointing so you know where you ultimately RETURN to, and it can work to your advantage.

[pedja089]

I had similar ideas, but give up on them. I use something like this:

Gosub xx : If err=1 then goto yy

XX:
if something to triger going to err sub then
err=1 ' goto in different sub after retun
else
err=0 ' return and continue normally
endif

But if you must have gosub, without return, you can look up in datasheet of PIC, POP command. It should pop up stack, and free one space.

The TOS value is pulled off the return
stack and is discarded. The TOS value
then becomes the previous value that
was pushed onto the return stack.
This instruction is provided to enable
the user to properly manage the return
stack to incorporate a software stack

If I understand POP and PUSH commands, you could do something like this

If err=1 THEN
@ POP
GOTO ErrHandler
ENDIF

[mpgmike]

Don't use both. What was printed in the above post will GOTO a new address, then erase the RETURN address. This will generate a Stack Underflow condition and the PIC will "exhibit unpredictable behavior". Just use GOTO and leave the Stack alone.

[pedja089]

But if I understand correctly he want to goto and never return.
So you need to pop stack to prevent overflow.

[mpgmike]

Then yes, POP the Stack. Not sure when such an approach might be considered good programming practice, though.