mapper_0042.c


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static void mapper_0042_init(struct nes_state *state) {
	state->map.m0042.prg_offset = 0;
	state->map.m0042.chr_offset = 0;
}

static uint8_t mapper_0042_prg_read(struct nes_state *state, uint32_t addr) {
	if(addr >= 0x8000) {
		uint32_t base = state->map.m0042.prg_offset;
		return state->prg_rom[base + (addr - 0x8000)];
	}
	return 0;
}

static void mapper_0042_prg_write(struct nes_state *state, uint32_t addr, uint8_t value) {
	if(addr >= 0x8000) {
		uint32_t prg_bank = (value >> 4) & 3;
		uint32_t chr_bank = (value >> 0) & 3;

		state->map.m0042.prg_offset = prg_bank * 0x8000;
		state->map.m0042.chr_offset = chr_bank * 0x2000;
	}
}

static uint8_t mapper_0042_chr_read(struct nes_state *state, uint32_t addr) {
	return state->chr_rom[state->map.m0042.chr_offset + addr];
}

static void mapper_0042_chr_write(struct nes_state *state, uint32_t addr, uint8_t value) {
}