11.10.1 Interrupt Handler Example

The following example provides a Reset function and a default interrupt handler in assembly language. The default interrupt handler uses persistent data storage to keep a count of unexpected interrupts and/or error traps.

       .include "xc.inc"
       .text

       .global __reset
__reset:
       ;; takes control at device reset/power-on
       mov   #__SP_init,w15      ; initialize stack pointer
       mov   #__SPLIM_init,w0    ;  and stack limit register
       mov   w0,SPLIM          ;

       btst  RCON,#POR         ; was this a power-on reset?
       bra   z,start           ;  branch if not

       clr   FaultCount        ; else clear fault counter
       bclr  RCON,#POR         ;  and power-on bit
start:
       goto  main              ; start application

       .global __T1Interrupt
__T1Interrupt:
       ;; services timer 1 interrupts
       bclr  IFS0,#T1IF        ; clear the interrupt flag
       retfie                  ;  and return from interrupt

       .global __DefaultInterrupt
__DefaultInterrupt:
       ;; services all other interrupts & traps
       inc  FaultCount         ; increment the fault counter
       reset                   ;  and reset the device

       .section .pbss,persist  ; persistent data storage
       .global FaultCount      ;  is not affected by reset
FaultCount:
       .space 2                ; count of unexpected interrupts

The standard naming conventions for interrupt handlers are described in the sections below.