Strange behaviour of my PBP code. [Archive]

Fredrick

- 22nd August 2009, 20:13

I have a strange "bug" in my PBP program that I can´t understand.

I have taken out the code that contains the bug from my bigger program and run it on two different PIC´s on two different devboards and the bug is still there so it must have something with the software to do.

The code lets you to select number of shooters (1-5), if Shooters = 2 the Status_LED will blink 2 times and then delay for a longer time before the next two blink.

You change the Shooters value by pressing SW_Forward or SW_Reverse, SW_Launch will start the rest of the program (not included) with the number of shooters stored in the variable Shooters.

The code works pretty well until yesterday when I tried to press the SW_Forward button for about 10 - 15 times as fast that I could then the program hangs and the Status_LED is constantly on, it looks like the program goes into a never ending loop and I must Reset the PIC to continue. the same thing will happen if I press SW_Reverse as fast I can.

Well the program works, but I want to know why the program hangs when I press the SW_Forward or SW_Reverse buttons several times fast

<html>
<head></head>
<body><pre><code>Define OSC 8
Include "alldigital.pbp" ;DT´s All Digital
Define SHOWDIGITAL 1

Asm ;================================================= ==========================
__CONFIG _CONFIG1L, _PLLDIV_5_1L & _CPUDIV_OSC1_PLL2_1L & _USBDIV_2_1L
__CONFIG _CONFIG1H, _FOSC_HS_1H
__CONFIG _CONFIG2H, _WDT_OFF_2H & _WDTPS_512_2H
__CONFIG _CONFIG3H, _PBADEN_OFF_3H
__CONFIG _CONFIG4L, _LVP_OFF_4L & _XINST_OFF_4L & 0DFh
Endasm;-------------------------------------------------------------------------

Shooters Var Byte
i Var Byte
Delayi Var Byte

SW_Launch Var PORTA.0;================================================= ======
SW_Reverse Var PORTA.1
SW_Forward Var PORTA.2
Status_LED Var PORTC.0;-------------------------------------------------------

Shooters = 2 ;Default value

Main:;================================================= =========================
Gosub Delay2

For i = 1 To Shooters
High Status_LED
Gosub Delay1
Low Status_LED
Gosub Delay1
Next i
Goto Main;----------------------------------------------------------------------

Delay1:;================================================= =======================
For Delayi = 0 To 100
Pause 2
Gosub Check_Buttons
Next Delayi
Return

Delay2:
For Delayi = 0 To 255
Pause 5
Gosub Check_Buttons
Next Delayi
Return;-------------------------------------------------------------------------

Check_Buttons:;================================================= ================
If SW_Launch = 0 Then
High Status_LED
Pause 50
While SW_Launch = 0: Wend
Pause 50
' goto start_new
Endif

If SW_Forward = 0 Then
High Status_LED
Pause 50
Shooters = Shooters + 1
If Shooters > 5 Then Shooters = 1
While SW_Forward = 0:Wend
Pause 50
Low Status_LED
Goto Main
Endif

If SW_Reverse = 0 Then
High Status_LED
Pause 50
Shooters = Shooters - 1
If Shooters < 1 Then Shooters = 5
While SW_Reverse = 0:Wend
Pause 50
Low Status_LED

Goto Main
Endif
Return;-------------------------------------------------------------------------

</code></pre></body>
</html>

Fredrick

- 22nd August 2009, 23:47

Ok.. now I have tested with another PIC,a PIC16F887 and then it works, the "bug" is gone.
So why does it hang with a PIC18F2550, PIC184550, and 18F4520?

Does it have something with the config fuses to do? what have I missed?

Darrel Taylor

- 23rd August 2009, 00:45

Hi Fredrick,

In the Check_Buttons subroutine, there's 2 Goto Main statements.

You should use RETURN to exit a subroutine.

Using GOTO will cause the stack to overflow.
With 18F's a stack overflow can cause a Reset.

But with 16F's the stack just wraps around and seems to work, although it's probably not working 100%.

Fredrick

- 23rd August 2009, 17:15

Ohh so simple!

When I notified the problem fist time I was saying to myself that this time I will try to solve the problem without help from anybody, so I have spent a lot off hours on trying to find the problem, but then I give up and started a thread here again.

Thank you Darrel.

Fredrick

- 23rd August 2009, 19:40

But it´s OK to use Goto´s within the subroutine as long as I call a label that is in the subroutine and only leave the subroutine by doing a Return

Darrel Taylor

- 23rd August 2009, 20:21

Exactly!

You've got it now. http://www.picbasic.co.uk/forum/images/icons/icon14.gif

Fredrick

- 24th August 2009, 11:19

How is it with variables?
If I overflow a byte sized counter it will turn to 0 after passing 255, but is it OK to let a variable overflow? or should I take care of the overflow like this

IF Counter > 254 Then
Counter = 0
Endif

Darrel Taylor

- 24th August 2009, 20:20

For BYTE sized variables, when the value goes over 255 the upper bits are lost, which makes it automatically wrap around to 0.
You don't need to do it manually.

For words, it wraps when over 65535.