Converting PBP interrupt to ASM - 18F25K20

[achilles03]

I have a couple interrupt routines using DT's instant interrupts in PBP that I'd like to convert to asm to reduce execution time. One of the ISRs uses an external interrupt to time pulses and store the results in an array (ppm) and increments to the array index (ppm_n). Bit 4 of ppm_n is set to 0 so that ppm_n rolls over from 15 to 0. I read the array outside of the interrupt and verify the bit ppmwrite hasn't changed while reading the data, else the interrupt could have occured while reading the data.

This compiles but it appears none of the array values are updating except for index 15, which appears to be randomly assigned and never changes even though the array is cleared at startup. However it appears the index ppm_n is incrementing and ppmwrite is being toggled. Typical output from the code below looks like this (first 16 values are the ppm array, red is ppm_n, and blue is ppmwrite):

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 29184 8 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 29184 6 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 29184 5 1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 29184 3 1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 29184 2 0

I cobbled together the code below from some helpful posts in these forums and the datasheet. I still include "ReEnterPBP-18.bas" since I use that for another ISR that still uses PBP, but that is not included in this test code. I'm not that experienced with asm (yet), so any pointers are greatly appreciated!

pausetime   var   word
ppm         var   word[16]
ppm_n       var   byte
n           var   byte
ppmwrite    var   bit

T3CON = %10110000 'ppm timer: Prescaler = 8:1,  Timer off; bit 5-4 is prescaler (00=1:1, 01=2:1 ... 11=8:1)

INCLUDE "DT_INTS-18.bas" ' Base Interrupt System
INCLUDE "ReEnterPBP-18.bas" ' Include if using PBP interrupts

'----[High Priority PPM Interrupt]----------------------------------------------
ASM
INT_LIST macro ; IntSource, Label, Type, ResetFlag?
INT_Handler INT0_INT, _PULSE_WIDTH, ASM, yes 
endm
INT_CREATE ; Creates the interrupt processor
ENDASM

'clear ppm array
for n=0 to 15
ppm[n]=0
next n

ppm_n=0

@ bsf     T3CON, TMR3ON   ; Start timer 
@ INT_ENABLE INT0_INT ; enable external (INT) interrupts

ppmloop:
pause 100
@ INT_DISABLE INT0_INT ; disble external (INT) interrupts
serout2 PIN_OUT,6,[dec ppm[0]," ",dec ppm[1]," ",dec ppm[2]," ",dec ppm[3]," ",dec ppm[4]," ",dec ppm[5]," ",dec ppm[6]," ",dec ppm[7]," ",dec ppm[8]," ",dec ppm[9]," ",dec ppm[10]," ",dec ppm[11]," ",dec ppm[12]," ",dec ppm[13]," ",dec ppm[14]," ",dec ppm[15]," ",dec ppm_n," ",dec ppmwrite,13,10]
@ INT_ENABLE INT0_INT ; enable external (INT) interrupts
goto ppmloop

PULSE_WIDTH:
ASM
   movff  TMR3L, _pausetime           ; Read LB and store in variable 'pausetime' - also loads TMR3H into buffer
   movff  TMR3H, _pausetime + 1       ; Read HB from buffer
   movf   _ppm_n, W                   ; Get index value from variable 'ppm_n' for array address, store in WREG
   rlncf  WREG, W                     ; Multiply by 2 since ppm array is words (16bit)
   addlw  _ppm                        ; add base address of ppm array to offset in W
   movwf  FSR0                        ; store the calculated address in FSR0
   movf   _pausetime, W               ; load pausetime LB into WREG
   movwf  INDF0                       ; move LB into ppm[ppm_n] 
   incf   FSR0                        ; move to next pointer loation for HB
   movf   _pausetime + 1, W           ; load pausetime HB into WREG
   movwf  INDF0                       ; move HB into ppm[ppm_n] 	
   incf   _ppm_n, f                   ; increment array index variable ppm_n
   bcf    _ppm_n, 4                   ; clear bit 4 so array starts over after index 15 (b1111)
   btg    _ppmwrite                   ; toggle ppmwrite to check if interrupt occured in main program
INT_RETURN
ENDASM

[achilles03]

I might have figured it out. It looks like I wasn't loading the full pointer into FSR0 since it's a 12-bit pointer. Also I hit on the POSTINC0 option, which is nifty. I believe the ISR should be something like this (see below). I am currently assuming that word arrays in PBP are allocated with the low byte in the lower address and the high byte at the next address (I need to verify this). Any errors in the code or any suggestions to consolidate instructions are much appreciated!

PULSE_WIDTH:
ASM
   movff  TMR3L, _pausetime           ; Read LB and store in variable 'pausetime' - also loads TMR3H into buffer
   movff  TMR3H, _pausetime + 1       ; Read HB from buffer
   lfsr   FSR0,  _ppm                 ; Load the full 12-bit address of ppm into FSR0
   movf   _ppm_n, W                   ; Get index value from variable 'ppm_n' for array address, store in WREG
   rlncf  WREG, W                     ; Multiply by 2 since ppm array is words (16bit)
   addwf  FSR0L, f                    ; Add offset to low byte of pointer
   movlw  0                           ; clear WREG although carry flag is still active in STATUS REGISTER bit 0 (pretty sure that's how it works?)
   addwfc FSR0H, f                    ; Add carry to high byte of pointer
   movf   _pausetime, W               ; Load pausetime LB into WREG  
   movwf  POSTINC0                    ; Store pausetime LB in ppm location and automatically increment FSR0
   movf   _pausetime + 1, W           ; Load pausetime HB into WREG     
   movwf  INDF0                       ; Store pausetime HB in ppm location
   incf   _ppm_n, f                   ; increment array index variable ppm_n
   bcf    _ppm_n, 4                   ; clear bit 4 so array starts over after index 15 (b1111)
   btg    _ppmwrite                   ; toggle ppmwrite to check if interrupt occured in main program
INT_RETURN
ENDASM