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181 lines
5.4 KiB
ArmAsm
181 lines
5.4 KiB
ArmAsm
;
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; Start-up code for cc65 (NES version)
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;
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; by Groepaz/Hitmen <groepaz@gmx.net>
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; based on code by Ullrich von Bassewitz <uz@cc65.org>
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;
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.export _exit
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.export __STARTUP__ : absolute = 1 ; Mark as startup
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.import initlib, donelib, callmain
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.import push0, _main, zerobss, copydata
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.import ppubuf_flush
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; Linker-generated symbols
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.import __RAM_START__, __RAM_SIZE__
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.import __SRAM_START__, __SRAM_SIZE__
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.import __ROM0_START__, __ROM0_SIZE__
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.import __STARTUP_LOAD__,__STARTUP_RUN__, __STARTUP_SIZE__
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.import __CODE_LOAD__,__CODE_RUN__, __CODE_SIZE__
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.import __RODATA_LOAD__,__RODATA_RUN__, __RODATA_SIZE__
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; ------------------------------------------------------------------------
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; Character data
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; ------------------------------------------------------------------------
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.forceimport NESfont
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.include "zeropage.inc"
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.include "nes.inc"
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; ------------------------------------------------------------------------
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; 16-byte INES header
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.segment "HEADER"
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; +--------+------+------------------------------------------+
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; | Offset | Size | Content(s) |
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; +--------+------+------------------------------------------+
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; | 0 | 3 | 'NES' |
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; | 3 | 1 | $1A |
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; | 4 | 1 | 16K PRG-ROM page count |
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; | 5 | 1 | 8K CHR-ROM page count |
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; | 6 | 1 | ROM Control Byte #1 |
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; | | | %####vTsM |
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; | | | | ||||+- 0=Horizontal mirroring |
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; | | | | |||| 1=Vertical mirroring |
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; | | | | |||+-- 1=SRAM enabled |
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; | | | | ||+--- 1=512-byte trainer present |
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; | | | | |+---- 1=Four-screen mirroring |
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; | | | | | |
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; | | | +--+----- Mapper # (lower 4-bits) |
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; | 7 | 1 | ROM Control Byte #2 |
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; | | | %####0000 |
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; | | | | | |
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; | | | +--+----- Mapper # (upper 4-bits) |
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; | 8-15 | 8 | $00 |
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; | 16-.. | | Actual 16K PRG-ROM pages (in linear |
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; | ... | | order). If a trainer exists, it precedes |
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; | ... | | the first PRG-ROM page. |
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; | ..-EOF | | CHR-ROM pages (in ascending order). |
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; +--------+------+------------------------------------------+
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.byte $4e,$45,$53,$1a ; "NES"^Z
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.byte 2 ; ines prg - Specifies the number of 16k prg banks.
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.byte 1 ; ines chr - Specifies the number of 8k chr banks.
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.byte %00000011 ; ines mir - Specifies VRAM mirroring of the banks.
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.byte %00000000 ; ines map - Specifies the NES mapper used.
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.byte 0,0,0,0,0,0,0,0 ; 8 zeroes
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; ------------------------------------------------------------------------
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; Place the startup code in a special segment.
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.segment "STARTUP"
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start:
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; Set up the CPU and System-IRQ.
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sei
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cld
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ldx #0
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stx VBLANK_FLAG
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stx ringread
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stx ringwrite
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stx ringcount
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txs
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lda #$20
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@l: sta ringbuff,x
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sta ringbuff+$0100,x
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sta ringbuff+$0200,x
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inx
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bne @l
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; Clear the BSS data.
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jsr zerobss
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; Initialize the data.
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jsr copydata
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; Set up the stack.
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lda #<(__SRAM_START__ + __SRAM_SIZE__)
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ldx #>(__SRAM_START__ + __SRAM_SIZE__)
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sta sp
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stx sp+1 ; Set argument stack ptr
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; Call the module constructors.
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jsr initlib
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; Push the command-line arguments; and, call main().
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jsr callmain
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; Call the module destructors. This is also the exit() entry.
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_exit: jsr donelib ; Run module destructors
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; Reset the NES.
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jmp start
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; ------------------------------------------------------------------------
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; System V-Blank Interrupt
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; Updates PPU Memory (buffered).
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; Updates VBLANK_FLAG and tickcount.
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; ------------------------------------------------------------------------
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nmi: pha
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tya
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pha
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txa
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pha
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lda #1
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sta VBLANK_FLAG
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inc tickcount
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bne @s
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inc tickcount+1
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@s: jsr ppubuf_flush
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; Reset the video counter.
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lda #$20
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sta PPU_VRAM_ADDR2
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lda #$00
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sta PPU_VRAM_ADDR2
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; Reset scrolling.
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sta PPU_VRAM_ADDR1
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sta PPU_VRAM_ADDR1
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pla
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tax
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pla
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tay
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pla
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; Interrupt exit
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irq:
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rti
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; ------------------------------------------------------------------------
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; Hardware vectors
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; ------------------------------------------------------------------------
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.segment "VECTORS"
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.word nmi ; $fffa vblank nmi
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.word start ; $fffc reset
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.word irq ; $fffe irq / brk
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