Add registers.asm file. Refer to registers by name.
This commit is contained in:
Colin McMillen
parent
6d94f5d032
commit
1925869fb6
47
pewpew.asm
47
pewpew.asm
@ -1,6 +1,6 @@
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.INCLUDE "header.asm"
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.INCLUDE "InitSNES.asm"
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.INCLUDE "registers.asm"
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.BANK 0 SLOT 0
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.ORG 0
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@ -11,31 +11,29 @@
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; 00-0F: scratch space for functions.
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; 10-13: controller state.
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; 14-17: 32-bit counter of vblanks.
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; 20-22: [rgb] color values to use for background color.
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; 20-22: RGB color values to use for background color, from [0-31].
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Start:
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InitSNES ; Initialize SNES.
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; Turn on the screen.
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; $2100: Screen display register [INIDISP]
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;
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; Format: x000bbbb
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; x: 0 = screen on, 1 = screen off, bbbb: Brightness ($0-$F)
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lda #%00001111
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sta $2100
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sta INIDISP
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; Enable NMI interrupt & joypad.
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; Register $4200: Counter enable [NMITIMEN]
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; n-vh---j n: NMI interrupt enable v: vertical counter enable
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; h: horizontal counter enable j: joypad enable
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lda #$81
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sta $4200
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sta NMITIMEN
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; Store zeroes to the controller status registers.
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; TODO(mcmillen): is this needed? I think the system should do this.
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stz $4218
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stz $4219
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; TODO(mcmillen): is this needed? I think the system will overwrite these
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; automatically.
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stz JOY1H
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stz JOY1L
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; Write something recognizable into our scratch space.
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jsr FillScratch
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@ -82,12 +80,11 @@ JoypadHandler:
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; Format: AXLR0000
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; $4219: Joypad #1 status [JOY1H]
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; Format: BYsSudlr (s=select, S=start, udlr = joypad)
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; Joypad #2 status would be $421A [JOY2L] and $421B [JOY2H].
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jsr JoypadDebug ; DEBUG
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; TODO(mcmillen): read joypad from local memory instead of registers?
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JoypadUp:
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lda $4219
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lda JOY1H
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and #$08 ; Up
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cmp #$08
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bne JoypadDown ; Button not pressed.
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@ -97,8 +94,8 @@ JoypadUp:
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inc $20
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JoypadDown:
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lda $4219
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and #$04 ; Down
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lda JOY1H
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and #$04
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cmp #$04
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bne JoypadLeft ; Button not pressed.
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lda $20
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@ -107,7 +104,7 @@ JoypadDown:
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dec $20
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JoypadLeft:
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lda $4219
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lda JOY1H
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and #$02 ; Left
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cmp #$02
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bne JoypadRight ; Button not pressed.
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@ -117,7 +114,7 @@ JoypadLeft:
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dec $22
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JoypadRight:
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lda $4219
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lda JOY1H
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and #$01
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cmp #$01 ; Right
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bne JoypadB ; Button not pressed.
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@ -127,7 +124,7 @@ JoypadRight:
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inc $22
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JoypadB:
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lda $4219
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lda JOY1H
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and #$80 ; B
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cmp #$80
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bne JoypadY ; Button not pressed.
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@ -137,7 +134,7 @@ JoypadB:
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inc $21
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JoypadY:
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lda $4219
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lda JOY1H
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and #$40 ; Y
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cmp #$40
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bne JoypadDone ; Button not pressed.
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@ -153,13 +150,13 @@ JoypadDone:
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JoypadDebug:
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; Load joypad registers into RAM for easier inspection.
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lda $4218
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lda JOY1L
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sta $10
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lda $4219
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lda JOY1H
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sta $11
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lda $421A
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lda JOY2L
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sta $12
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lda $421B
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lda JOY2H
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sta $13
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rts
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@ -175,7 +172,7 @@ SetBackgroundColor:
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asl
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.endr
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ora $20 ; Red.
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sta $2122
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sta CGDATA
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; Compute the high-order byte and store it in CGDATA.
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lda $22 ; Blue.
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@ -188,12 +185,12 @@ SetBackgroundColor:
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lsr
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.endr
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ora $00
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sta $2122
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sta CGDATA
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; Set the background color.
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; $2121 is the color palette selection register [CGADD].
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; Entry 0 corresponds to the SNES background color.
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stz $2121
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stz CGADD
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rts
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46
registers.asm
Normal file
46
registers.asm
Normal file
@ -0,0 +1,46 @@
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; Definitions of commonly-used special memory addresses.
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;
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; These are commonly called "registers" in online documentation, even though
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; that feels like a misnomer; these aren't necessarily hardware registers in
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; the same sense as PC, A, X, Y, and so on. Despite that, I call them
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; "registers" too, since that's what everyone else calls them.
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;
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; Where possible, I have named these register definitions in the same way that
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; they're named in Yoshi's venerable snes.txt document.
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; $2100: Screen display register [INIDISP]
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; Format: x000bbbb
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; x: 0 = screen on, 1 = screen off, bbbb: Brightness ($0-$F)
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.define INIDISP $2100
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; $2121: Color palette selection register [CGADD]
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; Entry 0 corresponds to the SNES background color.
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.define CGADD $2121
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; $2122: Color data register [CGDATA]
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; The palette color format is 15-bit: [0bbbbbgg][gggrrrrr].
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; You will typically write to this register twice in a row: first for the
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; low-order byte (containing green and red) and then for the high-order byte
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; (containing blue and green).
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.define CGDATA $2122
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; $4200: Counter enable [NMITIMEN]
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; n-vh---j n: NMI interrupt enable v: vertical counter enable
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; h: horizontal counter enable j: joypad enable
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.define NMITIMEN $4200
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; $4218: Joypad #1 status [JOY1L]
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; Format: AXLR0000
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.define JOY1L $4218
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; $4219: Joypad #1 status [JOY1H]
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; Format: BYsSudlr (s=select, S=start, udlr = joypad)
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.define JOY1H $4219
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; $421A: Joypad #2 status [JOY2L]
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; Format: AXLR0000
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.define JOY2L $421A
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; $421B: Joypad #2 status [JOY2H]
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; Format: BYsSudlr (s=select, S=start, udlr = joypad)
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.define JOY2H $421B
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