Add a "ship" and let the player move around.

This includes some tile / palette data in a separate file and some code
for DMA'ing that data into VRAM. This is used to render a "ship" (white
circle) that the player can move around with the D-Pad.

Added a whole bunch of named registers (& documentation for them) to
registers.asm.

InitSNES.asm

@@ -2,7 +2,7 @@
 ;-  Standard SNES initialization routine, originally by Neviksti
 ;------------------------------------------------------------------------
 
-.MACRO InitSNES
+.MACRO InitializeSNES
   sei                     ;disable interrupts
   clc                     ;switch to native mode
   xce

header.asm

@@ -12,7 +12,7 @@
 .SNESHEADER
   ID "SNES"
   
-  NAME "PEW PEW              "  ; Program title. Should be 21 bytes long;
+  NAME "PEW! PEW!            "  ; Program title. Should be 21 bytes long;
   ;    "123456789012345678901"  ; use spaces for unused bytes of the name.
 
   SLOWROM

pewpew.asm

@@ -2,6 +2,34 @@
 .INCLUDE "InitSNES.asm"
 .INCLUDE "registers.asm"
 
+
+; The JSR and RTS instructions add a total of 12 cycles of overhead.  For
+; short, commonly-used functions, it makes sense to declare them as macros,
+; which get inlined by the assembler at the point of use.  This saves on
+; CPU cycles, at the cost of code size.
+
+
+.MACRO ConvertXCoordinate
+; Data in: world x-coordinate, in A register.
+; Data out: SNES scroll data, in C (the 16-bit A register).
+rep #%00100000  ; 16-bit A
+eor #$FFFF  ; Flip bits
+ina
+sep #%00100000  ; 8-bit A
+.ENDM
+
+
+
+.MACRO ConvertYCoordinate
+; Data in: world y-coordinate, in A register.
+; Data out: SNES scroll data, in C (the 16-bit A register).
+rep #%00100000  ; 16-bit A
+eor #$FFFF  ; Flip bits
+sep #%00100000  ; 8-bit A
+.ENDM
+
+
+
 .BANK 0 SLOT 0
 .ORG 0
 .SECTION "MainCode"
@@ -9,14 +37,18 @@
 
 ; Memory layout:
 ; 00-0F: scratch space for functions.
-; 10-13: controller state.
+; 10-11: controller state of joypad #1.
+; 12-13: controller state of joypad #2.
 ; 14-17: 32-bit counter of vblanks.
-; 20-22: RGB color values to use for background color, from [0-31].
+; 20-21: (x, y) coordinates of player.
+; 22-24: RGB color values to use for background color, from [0-31].
 
 
 Start:
-    InitSNES  ; Initialize SNES.
+    InitializeSNES
-                      
+
+    jsr LoadPaletteAndTileData
+                    
     ; Turn on the screen. 
     ; Format: x000bbbb 
     ; x: 0 = screen on, 1 = screen off, bbbb: Brightness ($0-$F)
@@ -26,7 +58,7 @@ Start:
     ; Enable NMI interrupt & joypad.
     ; n-vh---j   n: NMI interrupt enable         v: vertical counter enable
     ;            h: horizontal counter enable    j: joypad enable
-    lda #$81
+    lda #%10000001
     sta NMITIMEN
 
     ; Store zeroes to the controller status registers.
@@ -38,6 +70,10 @@ Start:
     ; Write something recognizable into our scratch space.
     jsr FillScratch
 
+    ; Start the background color as a dark blue.
+    lda #16
+    sta $24
+
 
 
 MainLoop:
@@ -46,11 +82,77 @@ MainLoop:
 
 
 
+LoadPaletteAndTileData:
+    ; 16-bit X/Y registers. Used for DMA source address & transfer size, both of
+    ; which want 16-bit values.
+    ; TODO(mcmillen): change back to 8-bit when we're done?
+    rep #%00010000  
+    ; 8-bit A/B registers. Used for DMA source bank & destination address.
+    sep #%00100000
+
+    ; We only need one palette entry, so we just initialize it manually.
+    ; We could also do this with a DMA transfer (like we do with the tile data
+    ; below), but it seems overkill for just one entry :)
+    lda #34  ; Set the 34th palette entry.
+    sta CGADDR
+    lda.l PaletteData
+    sta CGDATA
+    lda.l PaletteData + 1
+    sta CGDATA
+
+    ; DMA 0 source address & bank.
+    ldx #TileData
+    stx DMA0SRC
+    lda #:TileData
+    sta DMA0SRCBANK
+    ; DMA 0 transfer size.
+    ldy #(15 * 16 *2)  ; Also see the helpful "480 bytes" comment in tiles.asm.
+    sty DMA0SIZE
+    ; DMA 0 control register.
+    ; Transfer type 001 = 2 addresses, LH.
+    lda #%00000001
+    sta DMA0CTRL
+    ; DMA 0 destination.
+    lda #$18  ; Upper-byte is assumed to be $21, so this is $2118 & $2119.
+    sta DMA0DST
+    ; $2116 sets the word address for accessing VRAM.
+    ldy #$0000
+    sty VMADDR
+    ; Enable DMA channel 0.
+    lda #%00000001
+    sta DMAENABLE
+
+    ; VRAM writing mode. Increments the address every time we write to $2119.
+    lda #%10000000
+    sta VMAIN
+    ; Set word address for accessing VRAM to $6000.
+    ldx #$6000  ; BG 2 starts here.
+    stx VMADDR
+    ldx #$000A  ; Stick one tile into BG2.
+    stx VMDATA
+
+    ; Set up the screen. 16x16 tiles for BG2, 8x8 tiles elsewhere, mode 0.
+    lda #%00100000
+    sta BGMODE
+    ; $2108 is the BG2 VRAM location register.
+    ; This tells it that the BG2 data starts at $6000.
+    lda #%01100000
+    sta BG2SC
+    stz BG12NBA
+
+    ; Main screen: enable BG2.
+    lda #%00000010
+    sta MSENABLE
+
+    rts
+
+
+
 VBlankHandler:
     jsr VBlankCounter  ; DEBUG
     jsr JoypadHandler
     jsr SetBackgroundColor
-    ; jsr FillScratch  ; DEBUG
+    jsr SetPlayerPosition
     rti
 
 
@@ -76,72 +178,113 @@ VBlankCounterDone:
 
 
 JoypadHandler:
-    ; $4218: Joypad #1 status [JOY1L]
-    ; Format: AXLR0000
-    ; $4219: Joypad #1 status [JOY1H]
-    ; Format: BYsSudlr (s=select, S=start, udlr = joypad)
     jsr JoypadDebug  ; DEBUG
 
-; TODO(mcmillen): read joypad from local memory instead of registers?
 JoypadUp:
     lda JOY1H
     and #$08  ; Up
     cmp #$08
     bne JoypadDown  ; Button not pressed.
-    lda $20
+    lda $21
-    cmp #31
+    cmp #0
     beq JoypadDown  ; Value saturated.
-    inc $20
+    dec $21
+    dec $21
 
 JoypadDown:
     lda JOY1H
     and #$04
     cmp #$04
     bne JoypadLeft  ; Button not pressed.
-    lda $20
+    lda $21
-    cmp #0
+    cmp #(224 - 16)
     beq JoypadLeft  ; Value saturated.
-    dec $20
+    inc $21
+    inc $21
 
 JoypadLeft:
     lda JOY1H
     and #$02  ; Left
     cmp #$02
     bne JoypadRight  ; Button not pressed.
-    lda $22
+    lda $20
     cmp #0
     beq JoypadRight  ; Value saturated.
-    dec $22
+    dec $20
+    dec $20
 
 JoypadRight:
     lda JOY1H
     and #$01
     cmp #$01  ; Right
     bne JoypadB  ; Button not pressed.
-    lda $22
+    lda $20
-    cmp #31
+    cmp #(256 - 16)
     beq JoypadB  ; Value saturated.
-    inc $22
+    inc $20
+    inc $20
 
 JoypadB:
     lda JOY1H
     and #$80  ; B
     cmp #$80
+    bne JoypadA  ; Button not pressed.
+    lda $22
+    cmp #0
+    beq JoypadA  ; Value saturated.
+    dec $22
+
+JoypadA:
+    lda JOY1L
+    and #$80  ; A
+    cmp #$80
     bne JoypadY  ; Button not pressed.
-    lda $21
+    lda $22
     cmp #31
     beq JoypadY  ; Value saturated.
-    inc $21
+    inc $22
 
 JoypadY:
     lda JOY1H
     and #$40  ; Y
     cmp #$40
-    bne JoypadDone  ; Button not pressed.
+    bne JoypadX  ; Button not pressed.
-    lda $21
+    lda $23
     cmp #0
+    beq JoypadX  ; Value saturated.
+    dec $23
+
+JoypadX:
+    lda JOY1L
+    and #$40  ; X
+    cmp #$40
+    bne JoypadL  ; Button not pressed.
+    lda $23
+    cmp #31
+    beq JoypadL  ; Value saturated.
+    inc $23
+
+JoypadL:
+    lda JOY1L
+    and #$20  ; L
+    cmp #$20
+    bne JoypadR  ; Button not pressed.
+    lda $24
+    cmp #0
+    beq JoypadR  ; Value saturated.
+    dec $24
+
+JoypadR:
+    lda JOY1L
+    and #$10  ; R
+    cmp #$10
+    bne JoypadDone  ; Button not pressed.
+    lda $24
+    cmp #31
     beq JoypadDone  ; Value saturated.
-    dec $21
+    inc $24
+
+; TODO(mcmillen): have Start and Select do something too.
 
 JoypadDone:
     rts  
@@ -163,34 +306,57 @@ JoypadDebug:
 
 
 SetBackgroundColor:
-    ; $20 $21 $22 are (R, G, B), each ranging from [0-31].
+    ; $22 $23 $24 are (R, G, B), each ranging from [0-31].
     ; The palette color format is 15-bit: [0bbbbbgg][gggrrrrr]
     
+    ; Set the background color.
+    ; Entry 0 corresponds to the SNES background color.
+    stz CGADDR
+
     ; Compute and the low-order byte and store it in CGDATA.
-    lda $21  ; Green.
+    lda $23  ; Green.
     .rept 5
         asl
     .endr
-    ora $20  ; Red.
+    ora $22  ; Red.
     sta CGDATA
 
     ; Compute the high-order byte and store it in CGDATA.
-    lda $22  ; Blue.
+    lda $24  ; Blue.
     .rept 2
         asl
     .endr
     sta $00
-    lda $21  ; Green.
+    lda $23  ; Green.
     .rept 3
         lsr
     .endr
     ora $00
     sta CGDATA
+    rts
 
-    ; Set the background color.
+
-    ; $2121 is the color palette selection register [CGADD].
+
-    ; Entry 0 corresponds to the SNES background color.
+SetPlayerPosition:
-    stz CGADD
+    ; Make sure the high byte of A is zeroed out.
+    lda #$00
+    xba
+    ; Get player x and convert it to a scroll offset.
+    lda $0020
+    ConvertXCoordinate
+    sta BG2HOFS
+    xba
+    sta BG2HOFS
+
+    ; Make sure the high byte of A is zeroed out.
+    lda #$00
+    xba
+    ; Get player y and convert it to a scroll offset.
+    lda $0021
+    ConvertYCoordinate
+    sta BG2VOFS
+    xba
+    sta BG2VOFS
     rts
 
 
@@ -206,3 +372,11 @@ FillScratchLoop:
     rts
 
 .ENDS
+
+
+
+.BANK 1 SLOT 0
+.ORG 0
+.SECTION "TileData"
+.INCLUDE "tiles.asm"
+.ENDS

registers.asm

@@ -5,17 +5,98 @@
 ; the same sense as PC, A, X, Y, and so on.  Despite that, I call them
 ; "registers" too, since that's what everyone else calls them.
 ;
-; Where possible, I have named these register definitions in the same way that
+; I've often named these register definitions in the same way that they're
-; they're named in Yoshi's venerable snes.txt document.
+; named in Yoshi's venerable snes.txt document.  In some cases (where the
+; mnemonic is too obscure) I've invented a different name.  In particular,
+; I've changed "ADD" to "ADDR" to reduce possible confusion between "addresses"
+; and "addition". The original name from Yoshi's doc is still listed in
+; brackets, like [CGADD], for easy cross-referencing.
+;
+; I've also heavily borrowed from Yoshi's descriptions of what these registers
+; do, though in many cases I've clarified / simplified the descriptions based
+; on my own understanding, or simply reformatted them a bit.
 
-; $2100: Screen display register [INIDISP]
+; $2100: Screen display initialization [INIDISP]
 ; Format: x000bbbb 
 ; x: 0 = screen on, 1 = screen off, bbbb: Brightness ($0-$F)
 .define INIDISP $2100
 
+; $2105: Screen mode register [BGMODE]
+; abcdefff    a: BG4 tile size (0=8x8, 1=16x16).
+;             b: BG3 tile size (0=8x8, 1=16x16).
+;             c: BG2 tile size (0=8x8, 1=16x16).
+;             d: BG1 tile size (0=8x8, 1=16x16).
+;             e: Highest priority for BG3 in MODE 1.
+;             f: MODE definition.
+.define BGMODE $2105
+
+; $2107-210A: BG1-4 VRAM location registers [BGxSC]
+; xxxxxxab    x: Base address
+;            ab: SC size     
+.define BG1SC $2107
+.define BG2SC $2108
+.define BG3SC $2109
+.define BG4SC $210A
+
+; $210B: BG1 & BG2 VRAM location register [BG12NBA]
+; $210C: BG3 & BG4 VRAM location register [BG34NBA]
+; aaaabbbb    a: Base address for BG2 (or BG4).
+;             b: Base address for BG1 (or BG3).
+.define BG12NBA $210B
+.define BG34NBA $210C
+
+; BG1 horizontal scroll offset. [BG1HOFS]
+; BG1 vertical scroll offset. [BG1VOFS]
+; ... and similar registers for BG2-4.
+; Write to all of these twice, as they want 2 bytes of data.
+; mmmmmaaa aaaaaaaa    a: Horizontal offset.
+;                      m: Only set with MODE 7.
+.define BG1HOFS $210D
+.define BG1VOFS $210E
+.define BG2HOFS $210F
+.define BG2VOFS $2110
+.define BG3HOFS $2111
+.define BG3VOFS $2112
+.define BG4HOFS $2113
+.define BG4VOFS $2114
+
+; $2115: Video port control [VMAIN]
+; i000abcd    i: 0 = Address increment after writing to $2118 or reading
+;                    from $2139.
+;                1 = Address increment after writing to $2119 or reading
+;                    from $213A.
+;            ab: Full graphic (see table below).
+;            cd: SC increment (see table below).
+;
+; abcd Result
+; 0100 Increment by 8 for 32 times (2-bit formation).
+; 1000 Increment by 8 for 64 times (4-bit formation).
+; 1100 Increment by 8 for 128 times (8-bit formation).
+; 0000 Address increments 1x1.
+; 0001 Address increments 32x32.
+; 0010 Address increments 64x64.
+; 0011 Address increments 128x128.
+.define VMAIN $2115
+
+; $2116-$2117: Video port address. 2 bytes. [VMADDL/VMADDH]
+.define VMADDR $2116
+
+; $2118-$2119: Video port data. 2 bytes. [VMDATAL/VMDATAH]
+; According to bit 7 of VMAIN, the data can be stored as:
+; Bit 7
+;   0    Write to $2118 only.          Lower 8-bits written then
+;                                      address is increased.
+;   0    Write to $2119 then $2118.    Address increased when both
+;                                      are written to (in order).
+;   1    Write to $2119 only.          Upper 8-bits written, then
+;                                      address is increased.
+;   1    Write to $2118 then $2119.    Address increased when both
+;                                      are written to (in order).
+.define VMDATA $2118
+
 ; $2121: Color palette selection register [CGADD]
 ; Entry 0 corresponds to the SNES background color.
-.define CGADD $2121
+.define CGADDR $2121
 
 ; $2122: Color data register [CGDATA]
 ; The palette color format is 15-bit: [0bbbbbgg][gggrrrrr].
@@ -24,11 +105,23 @@
 ; (containing blue and green).
 .define CGDATA $2122
 
+; $212C: Main screen designation [TM]
+; 000abcde    a: OBJ/OAM disable/enable.
+;             b: Disable/enable BG4.
+;             c: Disable/enable BG3.
+;             d: Disable/enable BG2.
+;             e: Disable/enable BG1.
+.define MSENABLE $212C
+
 ; $4200: Counter enable [NMITIMEN]
-; n-vh---j   n: NMI interrupt enable         v: vertical counter enable
+; n-vh---j    n: NMI interrupt enable         v: vertical counter enable
-;            h: horizontal counter enable    j: joypad enable
+;             h: horizontal counter enable    j: joypad enable
 .define NMITIMEN $4200
 
+; $420B: DMA enable [MDMAEN]
+; Each bit that's set enables one channel: 76543210
+.define DMAENABLE $420B
+
 ; $4218: Joypad #1 status [JOY1L]
 ; Format: AXLR0000
 .define JOY1L $4218
@@ -44,3 +137,38 @@
 ; $421B: Joypad #2 status [JOY2H]
 ; Format: BYsSudlr (s=select, S=start, udlr = joypad)
 .define JOY2H $421B
+
+; $43x0: DMA control for channel x. [DMAPX]
+; vh0cbaaa    v: 0 = CPU memory -> PPU.
+;                1 = PPU -> CPU memory.
+;             h: For HDMA only:
+;                0 = Absolute addressing.
+;                1 = Indirect addressing.
+;             c: 0 = Auto address inc/decrement.
+;                1 = Fixed address (for VRAM, etc.).
+;             b: 0 = Automatic increment.
+;                1 = Automatic decrement.
+;             a: Transfer type:
+;                000 = 1 address write twice: LH.
+;                001 = 2 addresses: LH.
+;                010 = 1 address write once.
+;                011 = 2 addresses write twice: LLHH
+;                100 = 4 addresses: LHLH
+.define DMA0CTRL $4300
+
+; $43x1: DMA destination for channel x. [BBADX]
+; The upper byte is assumed to be $21, so the possible destinations are
+; $2100-$21FF.
+.define DMA0DST $4301
+
+; $43x2-$43x3: DMA source address for channel x. 2 bytes. [AITXL/AITXH]
+.define DMA0SRC $4302
+
+; $43x4: DMA source bank for channel x [AIBX]
+.define DMA0SRCBANK $4304
+
+; $43x5: DMA transfer size & HDMA address. 2 bytes. [DASXL/DASXH]
+; When using DMA, $43x5 defines the # of bytes to be transferred via DMA
+; itself. When using HDMA, $43x5 defines the data address ($43x5 = low byte,
+; $43x6 = hi byte).
+.define DMA0SIZE $4305

tiles.asm

@@ -0,0 +1,39 @@
+; Created with eKid's pcx2snes converter ;
+
+TileData:
+    .db $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00
+    .db $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00
+    .db $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03
+    .db $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0
+    .db $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $FF, $FF, $FF, $FF
+    .db $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $FF, $FF, $FF, $FF
+    .db $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $FF, $FF, $FF, $FF
+    .db $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $FF, $FF, $FF, $FF
+    .db $00, $C0, $00, $E0, $00, $70, $00, $38, $00, $1C, $00, $0E, $00, $07, $00, $03
+    .db $00, $03, $00, $07, $00, $0E, $00, $1C, $00, $38, $00, $70, $00, $E0, $00, $C0
+    .db $00, $07, $00, $0F, $00, $18, $00, $30, $00, $60, $00, $C0, $00, $C0, $00, $C0
+    .db $00, $E0, $00, $F0, $00, $18, $00, $0C, $00, $06, $00, $03, $00, $03, $00, $03
+    .db $FC, $00, $F8, $00, $F0, $00, $E0, $00, $C0, $00, $80, $00, $00, $00, $00, $00
+    .db $3F, $00, $1F, $00, $0F, $00, $07, $00, $03, $00, $01, $00, $00, $00, $00, $00
+    .db $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00
+    .db $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00
+    .db $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00
+    .db $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00
+    .db $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03
+    .db $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0
+    .db $FF, $FF, $FF, $FF, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00
+    .db $FF, $FF, $FF, $FF, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00, $00
+    .db $FF, $FF, $FF, $FF, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03, $03
+    .db $FF, $FF, $FF, $FF, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0, $C0
+    .db $00, $03, $00, $07, $00, $0E, $00, $1C, $00, $38, $00, $70, $00, $E0, $00, $C0
+    .db $00, $C0, $00, $E0, $00, $70, $00, $38, $00, $1C, $00, $0E, $00, $07, $00, $03
+    .db $00, $C0, $00, $C0, $00, $C0, $00, $60, $00, $30, $00, $18, $00, $0F, $00, $07
+    .db $00, $03, $00, $03, $00, $03, $00, $06, $00, $0C, $00, $18, $00, $F0, $00, $E0
+    .db $00, $00, $00, $00, $80, $00, $C0, $00, $E0, $00, $F0, $00, $F8, $00, $FC, $00
+    .db $00, $00, $00, $00, $01, $00, $03, $00, $07, $00, $0F, $00, $1F, $00, $3F, $00
+
+PaletteData:
+    .db $FF, $7F
+
+; 30 tiles (2 spaces)
+; 480 bytes