Seeking Tips Converting from INTERRUPT to INTERRUPT NOPRESERVE

Yendor · 2008-08-04 21:00

I apologize if this is repeated in the forum (it's not coming back with any hits for INTERRUPT NOPRESERVE).

I'm needing to shave off a few cycles in my interrupt.

I'm trying to do some code optimization, but am tempted to use the NOPRESERVE feature.
·
I currently have some SX/B in the interrupt with some nested ·if..then.else statements that uses the __PARAM1 variable, like the following...

MOV FSR,MyVal                 ;  IF MyVal = 1 THEN
MOV __PARAM1,IND              
BANK $00                      
CJNE __PARAM1,#1,@i__ELSE_2   
;...etc

·And note that the asm code show it push and popping the parms before and after the interrupt code.

; save/preserve param1 and param2 

MOV FSR,#__INTPARAMFSR 

MOV IND,M 

INC FSR 
MOV IND,__PARAM1 

INC FSR 
MOV IND,__PARAM2 
;...__PARAM3...etc.
'interrupt code
;pop stack

Other than code optimization, upping the clock, and doubling the interrupt period/reducing the sampling rate of my interrupt, which may not work in my application, what would the 'pro' approach be in reducing the 'stack', and the interrupt clocks using INTERRUPT NOPRESERVE?·

Would it be to introduce·different global·variables to replace _PARAM1, or would it be to only preserve the variables the interrupt really needs to reuse ? e.g.·__INTPARAMFSR,·__PARAM1 in this case?

Many thanks!

Rodney

Post Edited (Yendor) : 8/4/2008 9:07:29 PM GMT

JonnyMac · 2008-08-04 22:17

If myVal was a global then the ISR wouldn't need indirect addressing; that might be an easy change. Or, you can borrow from SX/B (I do it a lot) and create your own "push" and "pop" code to protect the __PARAMx vars that might get used by the ISR:

Set your ISR to NOPRESERVE and then use this at the beginning of the ISR:

Push_Global:
  ASM
    MOV   FSR, #__INTPARAMFSR 
    MOV   IND, M 
    INC   FSR
    MOV   IND, __PARAM1
    BANK  $00
  ENDASM

And this right before the RETURNINT:

Pop_Global:
  ASM
    MOV   FSR, #__INTPARAMFSR
    MOV   M, IND
    INC   FSR
    MOV   __PARAM1, IND
    BANK  $00
  ENDASM

Yendor · 2008-08-05 16:21

Thanks for confirming Jon!

Seeking Tips Converting from INTERRUPT to INTERRUPT NOPRESERVE

Comments