79 lines
1.8 KiB
Zig
79 lines
1.8 KiB
Zig
const types = @import("types.zig");
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const Mirroring = types.Mirroring;
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const Mapper89 = @This();
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prg_bank: u8 = 0,
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chr_bank: u8 = 0,
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mirroring_mode: Mirroring = .single_screen_lower,
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prg_bank_count: usize,
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chr_bank_count: usize,
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pub fn init(
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prg_size: usize,
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chr_size: usize,
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) Mapper89 {
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return .{
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.prg_bank_count = prg_size / 0x4000,
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.chr_bank_count = if (chr_size > 0) chr_size / 0x2000 else 1,
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};
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}
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pub fn cpuMapRead(
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self: *const Mapper89,
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address: u16,
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) ?usize {
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if (address < 0x8000) return null;
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if (address < 0xC000) {
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const offset = @as(usize, address - 0x8000);
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const bank = @as(usize, self.prg_bank) % self.prg_bank_count;
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return bank * 0x4000 + offset;
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} else {
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const offset = @as(usize, address - 0xC000);
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const fixed_bank = if (self.prg_bank_count > 0) self.prg_bank_count - 1 else 0;
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return fixed_bank * 0x4000 + offset;
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}
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}
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pub fn cpuWrite(
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self: *Mapper89,
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address: u16,
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value: u8,
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) void {
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if (address >= 0x8000) {
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self.prg_bank = (value >> 4) & 0x07;
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self.chr_bank = (value & 0x07) | ((value & 0x80) >> 4);
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self.mirroring_mode = if ((value & 0x08) != 0) .single_screen_upper else .single_screen_lower;
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}
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}
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pub fn ppuMapRead(
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self: *const Mapper89,
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address: u16,
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) ?usize {
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if (address >= 0x2000) return null;
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const bank = @as(usize, self.chr_bank) % self.chr_bank_count;
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return bank * 0x2000 + @as(usize, address);
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}
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pub fn ppuMapWrite(
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_: *const Mapper89,
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address: u16,
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) ?usize {
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if (address >= 0x2000) return null;
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return address;
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}
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pub fn mirroring(
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self: *const Mapper89,
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) Mirroring {
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return self.mirroring_mode;
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}
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pub fn irqAsserted(_: *const Mapper89) bool {
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return false;
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}
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