History

S-CPU

S-CPU

• Registers
  • 3 general-purpose (A, X & Y)
  • 1 status
  • 2 addressing (D & DB)
  • Stack pointer (S)
  • Program counter (PC)
• 8- or 16-bit registers
• 24-bit address space
• 6502 emulation mode

• ---

  Max 3.58 MHz
• Multiplication and division

S-APU

S-APU

Musical scores

S-PPU

S-PPU

240p @ 60FPS

32K colors

16 palettes × 16 colors

4 background layers

128 sprites (64 × 64)

1 palette per sprite

S-PPU

S-PPU

S-PPU

S-PPU

S-PPU

Enhancements

Installed on cartridge

Super FX

Tools

Alternative

'development kits'

Programming

Skills and concepts

• 65816 assembly language
• Memory-mapped I/O
• Read/write ports and DMA
• V-Blank interrupt

Assembly

Opcodes and operands

                            01 clc                  ; Clear the CPU carry flag
02 xce                  ; Switch to 65816 native mode

03 .DEFINE CGDATA $2122 ; Use directive to define a named value

04 lda #$FF             ; Load the accumulator with the value 0xFF
05 sta CGDATA           ; Store the accumulator value in address $2121
                        

Assembly 2

Control flow

                            01 ; Wait for joypad auto-read
02 -   lda HVBJOY
03     bit #HVBJOY_JOYREADY
04     bne -

05     rep #$20   ; Reset accumulator to 16-bit
06     lda JOY1    ; Get joypad input
07     bit #JOY_UP ; Check if up was pressed on the D-pad
08     bne Up

09     bit #JOY_DOWN ; Check if down was pressed on the D-pad
10     bne Down
                        

Ports

Write color data to (CGRAM) 'through' a port

                            01 ; Set color 1 of palette 8 to white
02 lda #$81          ; Load destination address
03 sta CGADD         ; Set destination address (CGRAM)
04 lda #$FF          ; Load value (L)
05 sta CGDATA        ; Write value to port (CGRAM)
06 lda #$7F          ; Load value (H)
07 sta CGDATA        ; Write value to port (CGRAM)

08 ; Next color...
09 lda #$82          ; Load destination address
10 sta CGADD         ; Set destination address (CGRAM)
                        

Ports 2

Write pixel data to (VRAM) 'through' a port

                            01 lda #VMAINC_INC_H ; Increment after writing VMDATAH 
02 sta VMAINC        ; Set VRAM increment mode

03 ldx #$0400        ; Load destination address
04 stx VMADD         ; Set destination address (VRAM)

05 lda #%00000100    ; Load value (L)
06 sta VMDATAL       ; Write value to port (VRAM)
07 lda #%01110100    ; Load value (H)
08 sta VMDATAH       ; Write value to port (VRAM)

09 lda #%00000111
10 sta VMDATAL       ; Address was incremented automatically to #$0401
11 lda #%00000100
12 sta VMDATAH
                        

DMA

Transfer data between cartridge and VRAM

                            01 lda #%00000000    ; From A-bus to B-bus, read consecutive addresses
02 sta DMAP0         ; Set DMA control
03 lda #(CGDATA - BBUS_OFFSET)
04 sta BBAD0         ; Set DMA destination (8-bit B-bus is A-bus - $2100)
05 lda #Color        ; Address of the defined bytes at the Color label
06 sta A1T0          ; Set DMA source (A-bus)
07 lda #:Color       ; Get the bank of some defined bytes at the Color label
08 sta A1B0          ; Set the bank to use during DMA
09 lda #$02
10 sta DAS0L         ; Set DMA transfer size (number of bytes)
11 stz DAS0H
12 stz CGADD         ; Set starting address
13 lda #$01
14 sta MDMAEN        ; Initialize DMA transfer
                        

V-Blank interrupt

Callback every field/frame

                            01     .SNESNATIVEVECTOR ; WLA-DX directives
02         NMI VBlank
03     .ENDNATIVEVECTOR

04     ; Enable V-Blank
05     lda #NMITIMEN_NMI_ENABLE
06     sta NMITIMEN

07 -   wai
08     jmp -       ; Infinite loop

09 VBlank:
10     ; Callback code goes here...
                        

Programming 2

Using PPU features

• Colors
• Tiles
• Sprites
• Backgrounds

Colors

• Stored CGRAM (256 × 15bits)
• 16 palettes
• 16 colors per palette

Tiles

• Used for backgrounds and sprites
• Stored in VRAM (64KB) as 'characters'
• Planar bitmaps
• 8 by 8 pixels

Characters

• Planar bitmaps
• 2, 4 or 8 planes (layers)
• 1 or 0 from each separate plane is combined
• Resulting value determines color

                            
        Plane A
         0 | 1      Plane B
         - + -       1 | 1       Result
         1 | 0       - + -       1 | 2
                     0 | 0       - + -
                                 1 | 0
                            
                        

Sprites

Metadata for each sprite is stored in a OAM (544 bytes)

• X-coordinate
• Y-coordinate
• Character number (VRAM)
• Palette number
• Priority (Z-ordering)
• Horizontal/vertical flip
• Size

Backgrounds

Depends on background mode

Consist of tilemap(s) of 32 by 32 tiles

• Character number (VRAM)
• Palette number
• Priority (Z-ordering)
• Horizontal/vertical flip