use crate::cartridge::BaseMapper;
use crate::cartridge::mapper::{Mapper, MapperCapabilities};
pub struct Mapper41 {
base: BaseMapper,
prg_bank: u8,
chr_bank: u8,
}
impl Mapper41 {
const OUTER_REGISTER_START: u16 = 0x6000;
const OUTER_REGISTER_END: u16 = 0x67FF;
const INNER_REGISTER_START: u16 = 0x8000;
const INNER_REGISTER_END: u16 = 0xFFFF;
const PRG_BANK_MASK: u16 = 0x0007;
const CHR_OUTER_FROM_ADDR_MASK: u16 = 0x000C;
const CHR_INNER_MASK: u8 = 0x03;
const CHR_OUTER_MASK: u8 = 0x0C;
const MIRROR_HORIZONTAL_ADDR_BIT: u16 = 0x0020;
const INNER_ENABLE_PRG_THRESHOLD: u8 = 4;
pub fn new(ctx: super::mapper::MapperContext) -> Self {
let capabilities = MapperCapabilities {
has_chr_banking: true,
has_dynamic_mirroring: true,
max_prg_ram_kb: 0,
prg_bank_size_kb: 32,
chr_bank_size_kb: 8,
..Default::default()
};
let mut base = BaseMapper::new(&ctx, capabilities);
base.configure_prg_banking(32 * 1024);
base.configure_chr_banking(8 * 1024);
let mut mapper = Self {
base,
prg_bank: 0,
chr_bank: 0,
};
mapper.update_mapping();
mapper
}
fn update_mapping(&mut self) {
self.base.select_prg_page(0, self.prg_bank as i16);
self.base.select_chr_page(0, self.chr_bank as i16);
}
}
impl Mapper for Mapper41 {
fn base(&self) -> &BaseMapper {
&self.base
}
fn base_mut(&mut self) -> &mut BaseMapper {
&mut self.base
}
fn write_prg(&mut self, addr: u16, value: u8) {
if (Self::OUTER_REGISTER_START..=Self::OUTER_REGISTER_END).contains(&addr) {
self.prg_bank = (addr & Self::PRG_BANK_MASK) as u8;
self.chr_bank = (self.chr_bank & Self::CHR_INNER_MASK)
| (((addr >> 1) & Self::CHR_OUTER_FROM_ADDR_MASK) as u8);
self.base
.set_mirroring_hv((addr & Self::MIRROR_HORIZONTAL_ADDR_BIT) != 0);
self.update_mapping();
return;
}
if (Self::INNER_REGISTER_START..=Self::INNER_REGISTER_END).contains(&addr)
&& self.prg_bank >= Self::INNER_ENABLE_PRG_THRESHOLD
{
self.chr_bank = (self.chr_bank & Self::CHR_OUTER_MASK) | (value & Self::CHR_INNER_MASK);
self.update_mapping();
}
}
fn registers_snapshot(&self) -> Vec<u8> {
let mirroring_h = matches!(
self.base.mirroring(),
crate::cartridge::NametableLayout::Horizontal
);
vec![self.prg_bank, self.chr_bank, mirroring_h as u8]
}
fn restore_registers(&mut self, data: &[u8]) {
if data.len() >= 2 {
self.prg_bank = data[0];
self.chr_bank = data[1];
if data.len() >= 3 {
self.base.set_mirroring_hv(data[2] != 0);
}
self.update_mapping();
}
}
fn reset(&mut self) {
self.prg_bank = 0;
self.chr_bank = 0;
self.base
.set_mirroring(crate::cartridge::NametableLayout::Vertical);
self.update_mapping();
}
}
#[cfg(test)]
mod tests {
use super::Mapper41;
use crate::cartridge::NametableLayout;
use crate::cartridge::mapper::{Mapper, MapperContext, create_mapper};
use crate::cartridge::test_helpers::banked_data;
const PRG_BANKS_32K: usize = 11;
const CHR_BANKS_8K: usize = 13;
fn make_mapper() -> Box<dyn Mapper> {
create_mapper(MapperContext::new_for_test(
41,
banked_data(32 * 1024, PRG_BANKS_32K),
banked_data(8 * 1024, CHR_BANKS_8K),
NametableLayout::Vertical,
))
.expect("Mapper 41 should be implemented")
}
fn make_mapper_direct() -> Mapper41 {
Mapper41::new(MapperContext::new_for_test(
41,
banked_data(32 * 1024, PRG_BANKS_32K),
banked_data(8 * 1024, CHR_BANKS_8K),
NametableLayout::Vertical,
))
}
#[test]
fn mapper_41_is_registered_in_factory() {
let result = create_mapper(MapperContext::new_for_test(
41,
banked_data(32 * 1024, PRG_BANKS_32K),
banked_data(8 * 1024, CHR_BANKS_8K),
NametableLayout::Vertical,
));
assert!(
result.is_ok(),
"Mapper 41 must be registered in the factory"
);
}
#[test]
fn outer_register_selects_prg_bank_from_address_bits_0_to_2() {
let mut mapper = make_mapper_direct();
mapper.write_prg(0x6005, 0x00);
assert_eq!(mapper.read_prg(0x8000), 5);
}
#[test]
fn outer_register_selects_chr_outer_bits_from_address() {
let mut mapper = make_mapper_direct();
mapper.write_prg(0x6008, 0x00);
assert_eq!(mapper.read_chr(0x0000), 4);
}
#[test]
fn inner_chr_register_only_updates_when_prg_bank_is_4_to_7() {
let mut mapper = make_mapper_direct();
mapper.write_prg(0x6001, 0x00);
mapper.write_prg(0x8000, 0x03);
assert_eq!(mapper.read_chr(0x0000), 0, "inner write must be ignored");
mapper.write_prg(0x6004, 0x00);
mapper.write_prg(0x8000, 0x03);
assert_eq!(mapper.read_chr(0x0000), 3, "inner write must apply");
}
#[test]
fn outer_register_controls_mirroring_with_address_bit_5() {
let mut mapper = make_mapper_direct();
mapper.write_prg(0x6000, 0x00);
assert_eq!(mapper.get_mirroring(), NametableLayout::Vertical);
mapper.write_prg(0x6020, 0x00);
assert_eq!(mapper.get_mirroring(), NametableLayout::Horizontal);
}
#[test]
fn reset_clears_outer_and_inner_register_effects() {
let mut mapper = make_mapper_direct();
mapper.write_prg(0x6027, 0x00);
mapper.write_prg(0x8000, 0x03);
assert_ne!(mapper.read_prg(0x8000), 0);
assert_ne!(mapper.read_chr(0x0000), 0);
mapper.reset();
assert_eq!(mapper.read_prg(0x8000), 0);
assert_eq!(mapper.read_chr(0x0000), 0);
assert_eq!(mapper.get_mirroring(), NametableLayout::Vertical);
}
#[test]
fn snapshot_and_restore_roundtrip_register_state() {
let mut mapper = make_mapper_direct();
mapper.write_prg(0x6024, 0x00);
mapper.write_prg(0x8000, 0x02);
let snapshot = mapper.registers_snapshot();
let mut restored = make_mapper_direct();
restored.restore_registers(&snapshot);
assert_eq!(restored.read_prg(0x8000), mapper.read_prg(0x8000));
assert_eq!(restored.read_chr(0x0000), mapper.read_chr(0x0000));
}
#[test]
fn factory_mapper_exposes_same_behavior_surface() {
let mut mapper = make_mapper();
mapper.write_prg(0x6024, 0x00);
mapper.write_prg(0x8000, 0x01);
assert_eq!(mapper.read_prg(0x8000), 4);
assert_eq!(mapper.read_chr(0x0000), 1);
}
}