git.sur5r.net Git - cc65/blob - libsrc/vic20/irq.s

   1 ;
   2 ; IRQ handling (Vic20 version)
   3 ;
   4
   5         .export         initirq, doneirq
   6         .import         callirq
   7
   8         .include        "vic20.inc"
   9
  10 ; ------------------------------------------------------------------------
  11
  12 .segment        "INIT"
  13
  14 initirq:
  15         lda     IRQVec
  16         ldx     IRQVec+1
  17         sta     IRQInd+1
  18         stx     IRQInd+2
  19         lda     #<IRQStub
  20         ldx     #>IRQStub
  21         jmp     setvec
  22
  23 ; ------------------------------------------------------------------------
  24
  25 .code
  26
  27 doneirq:
  28         lda     IRQInd+1
  29         ldx     IRQInd+2
  30 setvec: sei
  31         sta     IRQVec
  32         stx     IRQVec+1
  33         cli
  34         rts
  35
  36 ; ------------------------------------------------------------------------
  37
  38 .segment        "LOWCODE"
  39
  40 IRQStub:
  41         cld                             ; Just to be sure
  42         jsr     callirq                 ; Call the functions
  43         jmp     IRQInd                  ; Jump to the saved IRQ vector
  44
  45 ; ------------------------------------------------------------------------
  46
  47 .data
  48
  49 IRQInd: jmp     $0000