+++ /dev/null
-; Nametables and attribute tables Demo for NES
-; Following on from the background palette program, this program looks at how
-; to load a pattern table, which contains the actual graphic tiles, a nametable,
-; which contains the layout of graphic tiles for the background, and the
-; attribute table, which specifies what palette to paint everything with.
-;
-; I am not an artist, and even then, converting bitmaps to pattern tables can be
-; a chore. So, I used the "Generitiles" from the NESDev wiki
-; (https://wiki.nesdev.com/w/index.php/Placeholder_graphics). I then ran these
-; through a Python script supplied by Damian Yerrick
-; (https://github.com/pinobatch/nesbgeditor) which converts a 2-bit PNG into
-; pattern tables pretty darn effectively. Thanks, Damian!
-;
-; So, we're now *finally* using the CHARS section, which gets directly mapped
-; into the PPU's memory at power on. This section really should more
-; be named "CHR-ROM", as this is the more common name for it. You'll notice
-; that I can directly include the file produced by Damian's tools, which keeps
-; the code tidy.
-;
-; With the patterns directly mapped in, the next step is to load up some data
-; in the name table. Since we're not doing anything fancy, I've restricted
-; things to the first of the two name tables. Much like we did for loading the
-; palette colors, we load this through the use of PPUADDR and PPUDATA.
-;
-; Finally, we load the attribute table, which says which palette to use for
-; each 32x32 pixel region on the screen. In a more advanced demo, this would
-; raise the number of effective colors I was using on the screen. For now,
-; though, I just want to keep things simple and easy-to-explain.
-;
-; Note that the annyoing "hello world" sound is now gone. The graphics show
-; that everything is working.
-
-.define PPUMASK $2001
-.define PPUSTATUS $2002
-.define PPUADDR $2006
-.define PPUSCROLL $2005
-.define PPUDATA $2007
-
-.define NAMETABLE_0_HI $20
-.define NAMETABLE_0_LO $00
-.define ATTRTABLE_0_HI $23
-.define ATTRTABLE_0_LO $C0
-.define BGPALETTE_HI $3F
-.define BGPALETTE_LO $00
-
-; Mandatory iNES header.
-.segment "HEADER"
-
-.byte "NES", $1A ; "NES" magic value
-.byte 2 ; number of 16KB code pages (we don't need 2, but nes.cfg declares 2)
-.byte 1 ; number of 8KB "char" data pages
-.byte $00 ; "mapper" and bank-switching type (0 for "none")
-.byte $00 ; background mirroring flats
- ;
- ; Note the header is 16 bytes but the nes.cfg will zero-pad for us.
-
-; code ROM segment
-; all code and on-ROM program data goes here
-
-.segment "STARTUP"
-
-; reset vector
-reset:
- bit PPUSTATUS ; clear the VBL flag if it was set at reset time
-vwait1:
- bit PPUSTATUS
- bpl vwait1 ; at this point, about 27384 cycles have passed
-vwait2:
- bit PPUSTATUS
- bpl vwait2 ; at this point, about 57165 cycles have passed
-
- ; Interesting little fact I learned along the way. Because it takes two
- ; stores on PPUADDR to move its pointer, it's good practice to start all of
- ; your PPUADDR use with a peek at PPUSTATUS since this resets its "latch"
- ; and ensures you're addressing the address you expect.
- ; Technically, we don't need this because we did it in the reset code, but
- ; it's a neat little thing to mention here
-
- bit PPUSTATUS
-
- ; load the background palette
- lda #BGPALETTE_HI
- sta PPUADDR
- lda #BGPALETTE_LO
- sta PPUADDR
-
- ; prep the loop
- ldx #0
-
-paletteloop:
- lda bgpalette, X ; load from the bgpalette array
- sta PPUDATA ; store in PPUDATA, PPU will auto-increment
- inx ; increment the X (index) register
- cpx #16
- bne paletteloop ; run the loop until X=16 (size of the palettes)
-
-; move PPUADDR over to nametable 0.
- lda #NAMETABLE_0_HI
- sta PPUADDR
- lda #NAMETABLE_0_LO
- sta PPUADDR
-
-; This loop iterates over the pattern table, outputting it in lines of 16
-; The other 16 are just padded out with a pattern that's blank. This lets
-; me easily show you some simple graphics that are made up of multiple
-; stacked tiles without getting too fancy. In reality, you'd probably have
-; complete nametables that you'd load in from files and simply run in a loop.
-
- ldx #$00
- ldy #16
-nametableloop:
- stx PPUDATA
- inx
- dey
- bne nametableloop
- ldy #16
-padright:
- sta PPUDATA
- dey
- bne padright
- cpx $D0
- beq done
- ldy #16
- jmp nametableloop
-done:
-
-; set up Palette 0 for everything
- bit PPUSTATUS
- lda #ATTRTABLE_0_HI
- sta PPUADDR
- lda #ATTRTABLE_0_LO
- sta PPUADDR
- ldx #64 ; 64 tiles in the attribute table
- lda #0
-
-attrloop:
- sta PPUDATA
- dex
- bne attrloop
-
-; Enable background and sprite rendering. This is suuuuuper important to
-; remember. I didn't remember to put this in and probably blew a whole day
-; trying to figure out why my emulator hated me.
- lda #$1e
- sta PPUMASK
-
-forever:
- jmp forever
-
-nmi:
- rti ; Return from the NMI (NTSC refresh interrupt)
-
-
-; The background colors are, in order:
-; $0F: black
-; $15: red
-; $22: blue
-; $20: white
-
-bgpalette:
- .byte $0F, $15, $22, $20 ; palette 0
- .byte $0F, $15, $22, $20 ; palette 1
- .byte $0F, $15, $22, $20 ; palette 2
- .byte $0F, $15, $22, $20 ; palette 3
-
-
-; vectors declaration
-.segment "VECTORS"
-.word nmi
-.word reset
-.word 0
-
-; As mentioned above, this is the place where you put your pattern table data
-; so that it can automatically be mapped into the PPU's memory at $0000-$1FFF.
-; Note the use of .incbin so I can just import a binary file. Neato!
-
-.segment "CHARS"
-.incbin "generitiles.pat"
--- /dev/null
+; Drawing static sprites
+; Now that we can confirm the palettes, pattern table, and nametable loading
+; are all working, we can work with the next part of the NES PPU-- the sprite
+; subsystem.
+;
+; Sprites are controlled by the Object Attribute Memory (OAM). There are 64
+; available entries in the OAM, with each specifying the coordinates and
+; pattern for the sprite. Sprites may be layered in front of or behind the
+; background, too (see Super Mario Bros 3 for a classic example of behind-the-
+; background sprite use).
+;
+; Technically, you can write to the OAM using addresses $2003 and $2004, called
+; OAMADDR and OAMDATA, but this is not commonly done because address $4014
+; manages a direct memory access (DMA) controller that can copy a complete OAM
+; table from the page of your choice in memory. By convention, most NES coders
+; use $0200, so writing 2 to $4014 triggers a dump into the PPU's OMA table.
+; The CPU is stalled during this transfer, so you need only make the write and
+; then carry on with the code.
+
+.define SPRITE_PAGE $0200
+
+.define PPUMASK $2001
+.define PPUSTATUS $2002
+.define PPUADDR $2006
+.define PPUSCROLL $2005
+.define PPUDATA $2007
+
+.define OAM_DMA $4014
+
+.define OAM_PAGE 2
+
+.define NAMETABLE_0_HI $20
+.define NAMETABLE_0_LO $00
+.define ATTRTABLE_0_HI $23
+.define ATTRTABLE_0_LO $C0
+.define BGPALETTE_HI $3F
+.define BGPALETTE_LO $00
+
+; Mandatory iNES header.
+.segment "HEADER"
+
+.byte "NES", $1A ; "NES" magic value
+.byte 2 ; number of 16KB code pages (we don't need 2, but nes.cfg declares 2)
+.byte 1 ; number of 8KB "char" data pages
+.byte $00 ; "mapper" and bank-switching type (0 for "none")
+.byte $00 ; background mirroring flats
+ ;
+ ; Note the header is 16 bytes but the nes.cfg will zero-pad for us.
+
+; code ROM segment
+; all code and on-ROM program data goes here
+
+.segment "STARTUP"
+
+; reset vector
+reset:
+ bit PPUSTATUS ; clear the VBL flag if it was set at reset time
+vwait1:
+ bit PPUSTATUS
+ bpl vwait1 ; at this point, about 27384 cycles have passed
+vwait2:
+ bit PPUSTATUS
+ bpl vwait2 ; at this point, about 57165 cycles have passed
+
+ ; Interesting little fact I learned along the way. Because it takes two
+ ; stores on PPUADDR to move its pointer, it's good practice to start all of
+ ; your PPUADDR use with a peek at PPUSTATUS since this resets its "latch"
+ ; and ensures you're addressing the address you expect.
+ ; Technically, we don't need this because we did it in the reset code, but
+ ; it's a neat little thing to mention here
+
+ bit PPUSTATUS
+
+ ; load the palettes
+ lda #BGPALETTE_HI
+ sta PPUADDR
+ lda #BGPALETTE_LO
+ sta PPUADDR
+
+ ; prep the loop
+ ldx #0
+
+; the palette loop now loads 8 palettes; 4 are for the background
+; tiles and 4 are for sprites. Before working with sprites, you
+; must set sprite palette colors, or you'll have a bad time
+
+paletteloop:
+ lda bgpalette, X ; load from the bgpalette array
+ sta PPUDATA ; store in PPUDATA, PPU will auto-increment
+ inx ; increment the X (index) register
+ cpx #32
+ bne paletteloop ; run the loop until X=32 (size of the palettes)
+
+; move PPUADDR over to nametable 0.
+ lda #NAMETABLE_0_HI
+ sta PPUADDR
+ lda #NAMETABLE_0_LO
+ sta PPUADDR
+
+; set up Palette 0 for everything
+ bit PPUSTATUS
+ lda #ATTRTABLE_0_HI
+ sta PPUADDR
+ lda #ATTRTABLE_0_LO
+ sta PPUADDR
+ ldx #64 ; 64 tiles in the attribute table
+ lda #0
+
+attrloop:
+ sta PPUDATA
+ dex
+ bne attrloop
+
+; Now for the meat of this lab-- making a sprite. This makes a
+; basic character using tiles we already have at hand from last lab's
+; pattern table. Note that the character is made up of six 8x8 tiles
+; and thus it takes six entries in the OAM to draw him. It's common
+; to think of "sprite" as "character," but on this early hardware,
+; all sprites are fixed sizes expressed in either 8x8 or 8x16 tiles.
+; So those 64 sprites don't go as far as it might seem!
+
+; zero out the OAM DMA shadow page
+ ldx #$FF
+ lda $0
+zero_oam:
+ sta SPRITE_PAGE, X
+ dex
+ bne zero_oam
+
+; refresh our index register...we're going to make heavy use of it
+; now...
+
+ ldx #0
+
+; head
+ lda #$7F ; Y coordinate
+ sta SPRITE_PAGE, X
+ inx
+ lda #$A0 ; Pattern bank 0, tile A0 (A1 is bottom)
+ sta SPRITE_PAGE, X
+ inx
+ lda #$00 ; No flipping, in front of background, palette 0
+ sta SPRITE_PAGE, X
+ inx
+ lda #$7F ; X coordinate
+ sta SPRITE_PAGE, X
+ inx
+ lda #$7F ; Y coordinate
+ sta SPRITE_PAGE, X
+ inx
+ lda #$A1 ; Pattern bank 0, tile A0 (A1 is bottom)
+ sta SPRITE_PAGE, X
+ inx
+ lda #$00 ; No flipping, in front of background, palette 0
+ sta SPRITE_PAGE, X
+ inx
+ lda #$87 ; X coordinate
+ sta SPRITE_PAGE, X
+ inx
+; torso
+ lda #$87 ; Y coordinate
+ sta SPRITE_PAGE, X
+ inx
+ lda #$B0 ; Pattern bank 0, tile A0 (A1 is bottom)
+ sta SPRITE_PAGE, X
+ inx
+ lda #$00 ; No flipping, in front of background, palette 0
+ sta SPRITE_PAGE, X
+ inx
+ lda #$7F ; X coordinate
+ sta SPRITE_PAGE, X
+ inx
+ lda #$87 ; Y coordinate
+ sta SPRITE_PAGE, X
+ inx
+ lda #$B1 ; Pattern bank 0, tile A0 (A1 is bottom)
+ sta SPRITE_PAGE, X
+ inx
+ lda #$00 ; No flipping, in front of background, palette 0
+ sta SPRITE_PAGE, X
+ inx
+ lda #$87 ; X coordinate
+ sta SPRITE_PAGE, X
+ inx
+; feet
+ lda #$8F ; Y coordinate
+ sta SPRITE_PAGE, X
+ inx
+ lda #$C0 ; Pattern bank 0, tile A0 (A1 is bottom)
+ sta SPRITE_PAGE, X
+ inx
+ lda #$00 ; No flipping, in front of background, palette 0
+ sta SPRITE_PAGE, X
+ inx
+ lda #$7F ; X coordinate
+ sta SPRITE_PAGE, X
+ inx
+ lda #$8F ; Y coordinate
+ sta SPRITE_PAGE, X
+ inx
+ lda #$C1 ; Pattern bank 0, tile A0 (A1 is bottom)
+ sta SPRITE_PAGE, X
+ inx
+ lda #$00 ; No flipping, in front of background, palette 0
+ sta SPRITE_PAGE, X
+ inx
+ lda #$87 ; X coordinate
+ sta SPRITE_PAGE, X
+
+; OAM DMA must always be a transfer from address XX00-XXFF, so we write
+; the value of XX (in this case, 2) to OAM_DMA ($4014) to trigger the
+; transfer
+
+ lda #OAM_PAGE
+ sta OAM_DMA
+
+; Enable background and sprite rendering.
+ lda #$1e
+ sta PPUMASK
+
+
+
+forever:
+ jmp forever
+
+nmi:
+ rti ; Return from the NMI (NTSC refresh interrupt)
+
+
+; The background colors are, in order:
+; $0F: black
+; $15: red
+; $22: blue
+; $20: white
+
+bgpalette:
+ .byte $0F, $15, $22, $20 ; palette 0
+ .byte $0F, $15, $22, $20 ; palette 1
+ .byte $0F, $15, $22, $20 ; palette 2
+ .byte $0F, $15, $22, $20 ; palette 3
+spritepalette:
+ .byte $0F, $07, $19, $20 ; palette 0
+ .byte $0F, $07, $19, $20 ; palette 1
+ .byte $0F, $07, $19, $20 ; palette 2
+ .byte $0F, $07, $19, $20 ; palette 3
+
+
+; vectors declaration
+.segment "VECTORS"
+.word nmi
+.word reset
+.word 0
+
+; As mentioned above, this is the place where you put your pattern table data
+; so that it can automatically be mapped into the PPU's memory at $0000-$1FFF.
+; Note the use of .incbin so I can just import a binary file. Neato!
+
+.segment "CHARS"
+.incbin "generitiles.pat"
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