reznez 0.0.0

The high accuracy NES Emulator
Documentation 
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use crate::memory::mapper::*;

const PRG_LAYOUT: PrgLayout = PrgLayout::new(&[
    PrgWindow::new(0x6000, 0x7FFF,  8 * KIBIBYTE, Bank::EMPTY),
    PrgWindow::new(0x8000, 0xBFFF, 16 * KIBIBYTE, Bank::switchable_rom(P0)),
    PrgWindow::new(0xC000, 0xFFFF, 16 * KIBIBYTE, Bank::fixed_rom(BankIndex::LAST)),
]);

const CHR_LAYOUT: ChrLayout = ChrLayout::new(&[
    ChrWindow::new(0x0000, 0x03FF, 1 * KIBIBYTE, Bank::switchable_rom(C0)),
    ChrWindow::new(0x0400, 0x07FF, 1 * KIBIBYTE, Bank::switchable_rom(C1)),
    ChrWindow::new(0x0800, 0x0BFF, 1 * KIBIBYTE, Bank::switchable_rom(C2)),
    ChrWindow::new(0x0C00, 0x0FFF, 1 * KIBIBYTE, Bank::switchable_rom(C3)),
    ChrWindow::new(0x1000, 0x13FF, 1 * KIBIBYTE, Bank::switchable_rom(C4)),
    ChrWindow::new(0x1400, 0x17FF, 1 * KIBIBYTE, Bank::switchable_rom(C5)),
    ChrWindow::new(0x1800, 0x1BFF, 1 * KIBIBYTE, Bank::switchable_rom(C6)),
    ChrWindow::new(0x1C00, 0x1FFF, 1 * KIBIBYTE, Bank::switchable_rom(C7)),
]);

const MIRRORINGS: [NameTableMirroring; 4] = [
    NameTableMirroring::Vertical,
    NameTableMirroring::Horizontal,
    NameTableMirroring::OneScreenLeftBank,
    NameTableMirroring::OneScreenRightBank,
];

// FCG-1 ASIC
pub struct Mapper016_4 {
    irq_pending: bool,
    irq_counter_enabled: bool,
    irq_counter: u16,
}

impl Mapper for Mapper016_4 {
    fn initial_layout(&self) -> InitialLayout {
        InitialLayout::builder()
            .prg_max_bank_count(16)
            .prg_bank_size(16 * KIBIBYTE)
            .prg_windows(PRG_LAYOUT)
            .chr_max_bank_count(256)
            .chr_bank_size(1 * KIBIBYTE)
            .chr_windows(CHR_LAYOUT)
            .name_table_mirroring_source(NameTableMirroringSource::Cartridge)
            .build()
    }

    fn write_to_cartridge_space(&mut self, params: &mut MapperParams, address: CpuAddress, value: u8) {
        match address.to_raw() & 0xE00F {
            0x0000..=0x401F => unreachable!(),
            0x4020..=0x5FFF => { /* Do nothing. */ }
            0x6000 => params.set_bank_register(C0, value),
            0x6001 => params.set_bank_register(C1, value),
            0x6002 => params.set_bank_register(C2, value),
            0x6003 => params.set_bank_register(C3, value),
            0x6004 => params.set_bank_register(C4, value),
            0x6005 => params.set_bank_register(C5, value),
            0x6006 => params.set_bank_register(C6, value),
            0x6007 => params.set_bank_register(C7, value),
            0x6008 => params.set_bank_register(P0, value & 0b1111),
            0x6009 => params.set_name_table_mirroring(MIRRORINGS[usize::from(value & 0b11)]),
            0x600A => {
                self.irq_pending = false;
                self.irq_counter_enabled = value & 1 == 1;
                if self.irq_counter_enabled && self.irq_counter == 0 {
                    self.irq_pending = true;
                }
            }
            0x600B => {
                // Set the low byte.
                self.irq_counter &= 0b1111_1111_0000_0000;
                self.irq_counter |= u16::from(value);
            }
            0x600C => {
                // Set the high byte.
                self.irq_counter &= 0b0000_0000_1111_1111;
                self.irq_counter |= u16::from(value) << 8;
            }
            0x600D..=0xFFFF => { /* Do nothing. */ }
        }
    }

    fn on_end_of_cpu_cycle(&mut self, _cycle: i64) {
        if self.irq_counter_enabled && self.irq_counter > 0 {
            self.irq_counter -= 1;
            if self.irq_counter == 0 {
                self.irq_pending = true;
            }
        }
    }
}

impl Mapper016_4 {
    pub fn new() -> Self {
        Self {
            irq_pending: false,
            irq_counter_enabled: false,
            irq_counter: 0,
        }
    }
}