GOTO vs RETURN after a GOSUB

[rsocor01]

Hi, I have the following code,

MainLoop:

'DO SOME STUFF HERE.....

    FOR J = 0 TO 7
        GOSUB SearchForClockSignal
    NEXT J

goto MainLoop

SearchForClockSignal:

    USBSERVICE
    SERIN2 PORTE.3, 32, 3, CLOCKSEARCHFAILED, [wait(252), STR RFID_IN\6]
    USBSERVICE 

    IF RFID_IN[0] = 252 THEN GOTO MAINLOOP  

    SquaresArray[0] = 255
    SquaresArray[1] = 202                       
    SquaresArray[2] = RFID_IN[0]                        
    SquaresArray[3] = RFID_IN[1]  
    SquaresArray[4] = RFID_IN[2]                        
    SquaresArray[5] = RFID_IN[3]
    SquaresArray[6] = RFID_IN[4]                        
    SquaresArray[7] = RFID_IN[5] 
    
    if PPB_DeviceState = 32 then   'ONLY WHEN THERE IS A USB CONNECTION PRESENT     
        GOSUB SendUSBData
    endif
    
    GOTO MAINLOOP   'CLOCK SERIAL COMMUNICATION WAS RECEIVED
    
CLOCKSEARCHFAILED:

RETURN

The program above will run for about 20 seconds and then it will stop working. Now, if I replaced the code in red "GOTO MAINLOOP" above by RETURN, then the code works just fine. Now, I understand that every GOSUB waits for a RETURN, but since I had the option "STACK OVERFLAW" disabled I thought that I could get away with it. Can somebody explains to me what is going on with this issue?

Thanks,

Robert

[pedja089]

Better question is why you would use GOSUB without RETURN? That just doesn't have any sense.
If stack is full then PBP can't call internal subroutines, and it crash...
You just disabled reset on overflow. That fuse doesn't expand stack to infinity and beyond.

Better solution to get same result

MainLoop:
 GOSUB SearchForClockSignal
goto MainLoop

SearchForClockSignal:
   FOR J = 0 TO 7
    USBSERVICE
    SERIN2 PORTE.3, 32, 3, CLOCKSEARCHFAILED, [wait(252), STR RFID_IN\6]
    USBSERVICE 

    IF RFID_IN[0] = 252 THEN RETURN 'GOTO MAINLOOP  

    SquaresArray[0] = 255
    SquaresArray[1] = 202                       
    SquaresArray[2] = RFID_IN[0]                        
    SquaresArray[3] = RFID_IN[1]  
    SquaresArray[4] = RFID_IN[2]                        
    SquaresArray[5] = RFID_IN[3]
    SquaresArray[6] = RFID_IN[4]                        
    SquaresArray[7] = RFID_IN[5] 
    
    if PPB_DeviceState = 32 then   'ONLY WHEN THERE IS A USB CONNECTION PRESENT     
        GOSUB SendUSBData
    endif
    
    RETURN   'CLOCK SERIAL COMMUNICATION WAS RECEIVED
    
CLOCKSEARCHFAILED:
    NEXT J
RETURN

[Dave]

It's probably overflowing the stack and halting.

[sayzer]

This should work.

MainLoop:

'DO SOME STUFF HERE.....

    FOR J = 0 TO 7
        GOTO SearchForClockSignal
    NEXT J

goto MainLoop

[rsocor01]

Better question is why you would use GOSUB without RETURN?

Yes, I'm asking myself the same question . Yes, your code looks better than mine. The program is probably overflowing the stack and halting like Dave said. Will the program restart from the beginning if the stack overflow is enabled?

[Dave]

Yes it should create an internal reset condition.

[pedja089]

Yes. It have almost same effect as MCLR pulled low, then high. Only 2 bits are different, if I remember correctly.

[rsocor01]

Thank you guys.

Robert

[Art]

If you want to be a cowboy for some reason you could have used GOTO instead of GOSUB.
Then you could GOTO back as well (instead of RETURN).

The difference between GOTO and GOSUB is that GOSUB loads the stack with the location it was called from so that a RETURN can go back there, but GOTO doesn’t need to do that.

BUT! using a GOTO to go somewhere, and another GOTO to go back, just means that neither GOTO had to exist, and you could have just dropped the routine right in where the GOTO was.

[Ioannis]

Also, using GOSUB reduces code size as this Sub can be called from various points of the program to do the same job, maybe with some parameters passing to it.

Keeps things structured.

Ioannis