mirror of
https://github.com/sehugg/8bitworkshop.git
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86 lines
2.2 KiB
C
86 lines
2.2 KiB
C
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/*
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Bank-switching using the MMC3 mapper.
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We use a special linker config that sets up
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64 KB of PRG ROM and 64 KB of CHR ROM.
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Macros are used to set MMC3 registers and switch banks.
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CC65 #pragma directives are used to put things in various
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PRG ROM segments (CODE0-CODE6, CODE).
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*/
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// bank-switching configuration
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#define NES_MAPPER 4 // Mapper 4 (MMC3)
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#define NES_PRG_BANKS 4 // # of 16KB PRG banks
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#define NES_CHR_BANKS 8 // # of 8KB CHR banks
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#include <peekpoke.h>
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#include <string.h>
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#include "neslib.h"
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// link the pattern table into CHR ROM
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//#link "chr_generic.s"
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#define MMC_MODE 0x00
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#define MMC3_SET_REG(r,n)\
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POKE(0x8000, MMC_MODE|(r));\
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POKE(0x8001, (n));
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#define MMC3_CHR_0000(n) MMC3_SET_REG(0,n)
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#define MMC3_CHR_0800(n) MMC3_SET_REG(1,n)
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#define MMC3_CHR_1000(n) MMC3_SET_REG(2,n)
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#define MMC3_CHR_1400(n) MMC3_SET_REG(3,n)
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#define MMC3_CHR_1800(n) MMC3_SET_REG(4,n)
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#define MMC3_CHR_1C00(n) MMC3_SET_REG(5,n)
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#define MMC3_PRG_8000(n) MMC3_SET_REG(6,n)
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#define MMC3_PRG_A000(n) MMC3_SET_REG(7,n)
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#define MMC3_MIRROR(n) POKE(0xa000, (n))
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#pragma rodata-name("CODE0")
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const unsigned char TEXT0[]={"Bank 0 @ 8000"};
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#pragma rodata-name("CODE1")
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const unsigned char TEXT1[]={"Bank 1 @ 8000"};
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#pragma rodata-name("CODE5")
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const unsigned char TEXT5[]={"Bank 5 @ A000"};
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#pragma rodata-name("CODE6")
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const unsigned char TEXT6[]={"Bank 6 @ C000"};
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// put functions in bank 1
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#pragma code-name("CODE1")
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void draw_text(word addr, const char* text) {
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vram_adr(addr);
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vram_write(text, strlen(text));
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}
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// back to main code segment
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#pragma code-name("CODE")
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void main(void)
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{
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// set palette colors
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pal_col(1,0x04);
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pal_col(2,0x20);
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pal_col(3,0x30);
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// setup CHR bank switching for background
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MMC3_CHR_0000(0);
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MMC3_CHR_0800(1);
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// select bank 0 in $8000-$9fff
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MMC3_PRG_8000(0);
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vram_adr(NTADR_A(2,2));
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vram_write(TEXT0, 13);
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// select bank 1 in $8000-$9fff
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// also needed to call draw_text()
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MMC3_PRG_8000(1);
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draw_text(NTADR_A(2,3), TEXT1);
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// select bank 5 in $a000-$bfff
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MMC3_PRG_A000(5);
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draw_text(NTADR_A(2,4), TEXT5);
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// $c000-$dfff is fixed to bank 6
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draw_text(NTADR_A(2,5), TEXT6);
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//enable rendering
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ppu_on_all();
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while(1);//do nothing, infinite loop
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}
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