rom.asm

   1         SECTION "a",HOME
   2
   3 main:
   4         ld c, $51       ; Note that we are alive.
   5         ld a, $FF
   6         ld [c],a
   7
   8         ld sp, $DFF0
   9
  10         ld hl, $DF81
  11         ld a, $80
  12         ld [hl], a
  13
  14         ld c, $07
  15         ld a, $04       ;start timer, 4.096KHz
  16         ld [c], a
  17 ;diqs:  ei
  18 ;       ld a, $80
  19 ;       ld c, $51
  20 ;       ld [c], a
  21 ;       jr diqs
  22         call irqhand
  23         ei
  24 coqs: jr coqs
  25
  26         section "Diq", HOME[$38]
  27 fuqed:
  28         di
  29         jr fuqed
  30
  31         section "fuq",HOME[$100]
  32 irqhand:
  33         PUSH AF
  34         PUSH BC
  35         PUSH DE
  36         PUSH HL
  37
  38         xor a
  39         ld c, $0F       ; ack the irq
  40         ld [c], a
  41
  42         ld a, $41       ; print A
  43         call putc
  44
  45         ld hl, $DF81
  46         ld a, [hl]
  47         add 1
  48         ld c, $51
  49         ld [c], a
  50         ld [hl], a
  51
  52
  53         POP HL
  54         POP DE
  55         POP BC
  56         POP AF
  57         RETI
  58         db $18,$FE,$18,$FE,$18,$FE,$18,$FE,$18,$FE,$18,$FE,$18,$FE,$18,$FE
  59         db $18,$FE,$18,$FE,$18,$FE,$18,$FE,$18,$FE,$18,$FE,$18,$FE,$18,$FE
  60         db $18,$FE,$18,$FE,$18,$FE,$18,$FE,$18,$FE,$18,$FE,$18,$FE,$18,$FE
  61
  62 putc:
  63         ld b, 0
  64         ld c, $50
  65         push af
  66 .waitport:
  67         ld a,[c]
  68         cp b
  69         jr nz,.waitport
  70         pop af
  71         ld [c],a
  72         ret