Simple SNES shoot-'em-up game.
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256 lines
6.7 KiB

;------------------------------------------------------------------------
;- Standard SNES initialization routine, originally by Neviksti
;------------------------------------------------------------------------
.MACRO InitializeSNES
sei ;disable interrupts
clc ;switch to native mode
xce
REP #$38 ; mem/A = 16 bit, X/Y = 16 bit
;decimal mode off
LDX #$1FFF ;Setup the stack
TXS ;Transfer Index X to Stack Pointer Register
;do the rest of the initialization in a routine
JSL $008000
SEP #$20 ; mem/A = 8 bit
.ENDM
;----------------------------------------------------------------------------
.BANK 0 SLOT 0
.ORG 0
.SECTION "InitializeSNESCode" FORCE
InitializeSNES:
PHK ;set Data Bank = Program Bank
PLB
LDA #$0000 ;set Direct Page = $0000
TCD ;Transfer Accumulator to Direct Register
LDX $1FFD ;we clear all the mem at one point ...
STX $4372 ;so save the return address in a place that won't get overwritten
LDX $1FFF
STX $4374
SEP #$20 ; mem/A = 8 bit
REP #$10
LDA #$8F
STA $2100 ;turn screen off for now, set brightness to normal
LDX #$2101
_Loop00: ;regs $2101-$210C
STZ $00,X ;set Sprite,Character,Tile sizes to lowest, and set addresses to $0000
INX
CPX #$210D
BNE _Loop00
_Loop01: ;regs $210D-$2114
STZ $00,X ;Set all BG scroll values to $0000
STZ $00,X
INX
CPX #$2115
BNE _Loop01
LDA #$80 ;reg $2115
STA $2115 ; Initialize VRAM transfer mode to word-access, increment by 1
STZ $2116 ;regs $2117-$2117
STZ $2117 ;VRAM address = $0000
;reg $2118-$2119
;VRAM write register... don't need to initialize
STZ $211A ;clear Mode7 setting
LDX #$211B
_Loop02: ;regs $211B-$2120
STZ $00,X ;clear out the Mode7 matrix values
STZ $00,X
INX
CPX #$2121
BNE _Loop02
;reg $2121 - Color address, doesn't need initilaizing
;reg $2122 - Color data, is initialized later
LDX #$2123
_Loop03: ;regs $2123-$2133
STZ $00,X ;turn off windows, main screens, sub screens, color addition,
INX ;fixed color = $00, no super-impose (external synchronization),
CPX #$2134 ;no interlaced mode, normal resolution
BNE _Loop03
;regs $2134-$2136 - multiplication result, no initialization needed
;reg $2137 - software H/V latch, no initialization needed
;reg $2138 - Sprite data read, no initialization needed
;regs $2139-$213A - VRAM data read, no initialization needed
;reg $213B - Color RAM data read, no initialization needed
;regs $213C-$213D - H/V latched data read, no initialization needed
STZ $213E ;reg $213E - might not be necesary, but selects PPU master/slave mode
;reg $213F - PPU status flag, no initialization needed
;reg $2140-$2143 - APU communication regs, no initialization required
;reg $2180 - read/write WRAM register, no initialization required
;reg $2181-$2183 - WRAM address, no initialization required
;reg $4016-$4017 - serial JoyPad read registers, no need to initialize
STZ $4200 ;reg $4200 - disable timers, NMI,and auto-joyread
LDA #$FF
STA $4201 ;reg $4201 - programmable I/O write port, initalize to allow reading at in-port
;regs $4202-$4203 - multiplication registers, no initialization required
;regs $4204-$4206 - division registers, no initialization required
;regs $4207-$4208 - Horizontal-IRQ timer setting, since we disabled this, it is OK to not init
;regs $4209-$420A - Vertical-IRQ timer setting, since we disabled this, it is OK to not init
STZ $420B ;reg $420B - turn off all general DMA channels
STZ $420C ;reg $420C - turn off all H-MA channels
STZ $420D ;reg $420D - ROM access time to slow (2.68Mhz)
LDA $4210 ;reg $4210 - NMI status, reading resets
;reg $4211 - IRQ status, no need to initialize
;reg $4212 - H/V blank and JoyRead status, no need to initialize
;reg $4213 - programmable I/O inport, no need to initialize
;reg $4214-$4215 - divide results, no need to initialize
;reg $4216-$4217 - multiplication or remainder results, no need to initialize
;regs $4218-$421f - JoyPad read registers, no need to initialize
;regs $4300-$437F
;no need to intialize because DMA was disabled above
;also, we're not sure what all of the registers do, so it is better to leave them at
;their reset state value
JSR ClearVRAM ;Reset VRAM
JSR ClearPalette ;Reset colors
;**** clear Sprite tables ********
STZ $2102 ;sprites initialized to be off the screen, palette 0, character 0
STZ $2103
LDX #$0080
LDA #$F0
_Loop08:
STA $2104 ;set X = 240
STA $2104 ;set Y = 240
STZ $2104 ;set character = $00
STZ $2104 ;set priority=0, no flips
DEX
BNE _Loop08
LDX #$0020
_Loop09:
STZ $2104 ;set size bit=0, x MSB = 0
DEX
BNE _Loop09
;**** clear WRAM ********
STZ $2181 ;set WRAM address to $000000
STZ $2182
STZ $2183
LDX #$8008
STX $4300 ;Set DMA mode to fixed source, BYTE to $2180
LDX #wram_fill_byte
STX $4302 ;Set source offset
LDA #:wram_fill_byte
STA $4304 ;Set source bank
LDX #$0000
STX $4305 ;Set transfer size to 64k bytes
LDA #$01
STA $420B ;Initiate transfer
LDA #$01 ;now set the next 64k bytes
STA $420B ;Initiate transfer
PHK ;make sure Data Bank = Program Bank
PLB
CLI ;enable interrupts again
LDX $4372 ;get our return address...
STX $1FFD
LDA $4374
STA $1FFF
RTL
wram_fill_byte:
.db $00
;----------------------------------------------------------------------------
; ClearVRAM -- Sets every byte of VRAM to zero
; In: None
; Out: None
; Modifies: flags
;----------------------------------------------------------------------------
ClearVRAM:
pha
phx
php
REP #$30 ; mem/A = 8 bit, X/Y = 16 bit
SEP #$20
LDA #$80
STA $2115 ;Set VRAM port to word access
LDX #$1809
STX $4300 ;Set DMA mode to fixed source, WORD to $2118/9
LDX #$0000
STX $2116 ;Set VRAM port address to $0000
STX $0000 ;Set $00:0000 to $0000 (assumes scratchpad ram)
STX $4302 ;Set source address to $xx:0000
LDA #$00
STA $4304 ;Set source bank to $00
LDX #$FFFF
STX $4305 ;Set transfer size to 64k-1 bytes
LDA #$01
STA $420B ;Initiate transfer
STZ $2119 ;clear the last byte of the VRAM
plp
plx
pla
RTS
;----------------------------------------------------------------------------
; ClearPalette -- Reset all palette colors to zero
; In: None
; Out: None
; Modifies: flags
;----------------------------------------------------------------------------
ClearPalette:
PHX
PHP
REP #$30 ; mem/A = 8 bit, X/Y = 16 bit
SEP #$20
STZ $2121
LDX #$0100
ClearPaletteLoop:
STZ $2122
STZ $2122
DEX
BNE ClearPaletteLoop
PLP
PLX
RTS
.ENDS