Crashing program

[Charles Linquis]

A couple of lines got left off. The basic flow is:
---------------------------------------------------------------------

DEFINE INTHAND IntSerial

(Setup main registers)

wsave VAR BYTE bankA system
ssave VAR BYTE bankA system
fsave VAR WORD bankA system

(Define other variables)


GOTO START

************** ISR STARTS HERE *************
asm
IntSerial

(Save W,STATUS,FSR0)

endasm

(BASIC PROGRAM to handle serial buffer, sets flag when carriage return received)


asm
(Restore W,STATUS,FSR0)
endasm

************ ISR ENDS HERE ***************

START:

(BASIC PROGRAM to handle buffer, do other things)

GOTO START

---------------------------------------------------------------

The program runs, but every once in awhile, I get odd port bits toggling.
Must I write my entire ISR in assembly, or can I keep it in BASIC as I am doing now?

[Bruce]

Hi Charles,

With assembler interrupts, you have two options.

1. Write your entire interrupt handler in assembler.

2. Save all PBP system variables on entry, and restore all PBP system
variables on exit, from your interrupt handler.

With assembler interrupts, you can interrupt any PBP command in mid-stroke.
What this means is you exit from "any" command whether it's completed
execution or not.

Then when you enter your interrupt handler, and use BASIC commands, you
are again using PBP system variables.

If you over-write a single system variable that was being used at the time
the interrupt occured, then once you return to the interrupted BASIC library
routine, there's a good chance you have corrupted whatever system variables
were being used by the interrupted BASIC library function.

Your program goes haywire, and the rest is history.

Darrel posted several excellent interrupt routines. Take a peek at this thread
http://www.picbasic.co.uk/forum/showthread.php?t=3251

The .lst file generated at compile time gives you a full list of all system vars
you'll need to save/restore during an assembler interrupt.

[sougata]

Hi,

What are you doing inside the basic routine ? If you are sure that you program is not taking much time for a single example then depending on the input baud rate / execution speed you can even handle the entire stuff in PBP. But if it needs to be fast then it is best to write in asm completely. Saving the PBP variables can be a little tricky if your code grows with future requirement. As you mentioned you are new to asm (so am I) give it a try and there are guys out here who can help. Keep the Faith

[Charles Linquis]

Unfortunately, Darrel himself states that the routines don't work with 18F parts - which is all I ever use.