common/nmi.asm

   1 .include "ppu.h"
   2 .include "sprite.h"
   3 .include "tablecall.h"
   4
   5 .ifdef MMC
   6 .if MMC == 3
   7 .include "../mmc/mmc3.h"
   8 .endif
   9 .endif
  10
  11 .dataseg
  12
  13 .extrn ppu:ppu_state
  14 .extrn sprites:byte
  15
  16 .ifdef MMC
  17 .if MMC == 3
  18 .extrn chr_banks:byte
  19 .extrn chr_addr_toggle:byte
  20 .extrn irq_count:byte
  21 .endif
  22 .endif
  23
  24 in_nmi .byte
  25 frame_count .byte
  26 main_cycle .byte
  27
  28 .public frame_count
  29 .public main_cycle
  30
  31 .codeseg
  32
  33 .public nmi
  34
  35 .extrn flush_ppu_buffer:proc
  36 .ifndef NO_JOYPAD0
  37 .extrn read_joypad:proc
  38 .endif
  39 .ifndef NO_JOYPAD1
  40 .extrn read_joypad1:proc
  41 .endif
  42 .ifndef NO_SOUND
  43 .extrn update_sound:proc
  44 .endif
  45 .extrn table_call:proc
  46 .extrn update_timers:proc
  47
  48 nmi:
  49     sei
  50     pha                     ; preserve A
  51     txa
  52     pha                     ; preserve X
  53     tya
  54     pha                     ; preserve Y
  55
  56     lda     ppu.ctrl1
  57     sta     PPU_CTRL1_REG
  58
  59     lda     in_nmi
  60     bne     skip_nmi        ; skip the next part if the frame couldn't
  61                             ; finish before the NMI was triggered
  62     inc     in_nmi
  63     inc     frame_count
  64
  65     jsr     flush_ppu_buffer
  66
  67 ; update PPU control register 0
  68     lda     ppu.ctrl0
  69     sta     PPU_CTRL0_REG
  70
  71 ; update scroll registers
  72     lda     PPU_STATUS_REG  ; reset H/V scroll flip flop
  73     lda     ppu.scroll_x
  74     sta     PPU_SCROLL_REG
  75     lda     ppu.scroll_y
  76     sta     PPU_SCROLL_REG
  77
  78 .ifndef NO_SPRITE_DMA
  79     lda     #0
  80     sta     SPRITE_ADDR_REG ; reset SPR-RAM address
  81     lda     #>sprites
  82     sta     SPRITE_DMA_REG
  83 .endif
  84
  85 .ifdef MMC
  86 .if MMC == 3
  87 ; set CHR banks
  88     ldx     #$05
  89   - txa
  90     ora     chr_addr_toggle
  91     sta     MMC3_CTRL_REG
  92     lda     chr_banks,x
  93     sta     MMC3_PAGE_REG
  94     dex
  95     bpl     -
  96
  97 ; set up IRQ if requested
  98     lda     irq_count
  99     beq     +
 100     sta     MMC3_IRQ_COUNTER_REG
 101     sta     MMC3_IRQ_LATCH_REG
 102     sta     MMC3_IRQ_ENABLE_REG
 103   +
 104 .endif
 105 .endif
 106
 107 ; read joypad(s)
 108 .ifndef NO_JOYPAD0
 109     jsr     read_joypad
 110 .endif
 111 .ifndef NO_JOYPAD1
 112     jsr     read_joypad1
 113 .endif
 114
 115 .ifndef NO_SOUND
 116     jsr     update_sound
 117 .endif
 118
 119 ; update timers
 120     jsr     update_timers
 121
 122     jsr     go_main_cycle
 123
 124     dec     in_nmi          ; = 0, NMI done
 125     skip_nmi:
 126     pla
 127     tay                     ; restore Y
 128     pla
 129     tax                     ; restore X
 130     pla                     ; restore A
 131     rti
 132
 133 go_main_cycle:
 134     lda     main_cycle
 135     jsr     table_call
 136 .include "maincycletable.asm"
 137
 138 .end