0xrsydn/gameboy-rust
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feat(cartridge): add 512-byte and 8 KiB serial EEPROM saves

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Select them with --save-type eeprom512 or eeprom8k. The part follows GBATEK's
protocol on Game Pak data bit 0: DMA3 sends one bit per halfword, '11' +
address + '0' requests a 64-bit block that reads back after four dummy bits,
and '10' + address + data + '0' writes one. A write reports busy for a nominal
108,368 cycles before the block is stored. 8 KiB parts decode the low 10
address bits. ROMs above 16 MiB map EEPROM only at 0x0dffff00..0x0dffffff.

Bits shift out only inside machine steps, so failed steps roll back. CPU
stores, byte/word accesses, CPU reads during a read-out, and malformed or
overlapping requests are diagnostics. Blocks are stored first-bit-as-MSB,
matching common .sav layouts, and work with save files and save states.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HhfHfHEuzv2AUTd6erW1gU
This commit is contained in:
0xrsydn 2026-10-14 12:06:17 +07:00
commit 652ea397f2
15 changed files with 828 additions and 24 deletions
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40
crates/gba-core/src/memory.rs
View file

@ -226,7 +226,7 @@ impl Memory {
);
self.save_image = vec![0xff; device.capacity()];
self.save_modified = false;
self.cartridge.set_save_device(device);
self.cartridge.set_save_device(device, self.rom.len());
}
/// Inspect the complete save array, independently of ID mode and selected bank.
@ -253,7 +253,7 @@ impl Memory {
}
self.save_image.copy_from_slice(bytes);
self.save_modified = false;
self.cartridge.set_save_device(device);
self.cartridge.set_save_device(device, self.rom.len());
Ok(())
}
@ -297,6 +297,11 @@ impl Memory {
self.save_modified |= target.iter().any(|&b| b != effect.value);
target.fill(effect.value);
}
if let Some((start, block)) = self.cartridge.take_save_block() {
let target = &mut self.save_image[start..start + block.len()];
self.save_modified |= *target != block;
target.copy_from_slice(&block);
}
}
fn cartridge_state(&self) -> Cartridge {
@ -864,6 +869,12 @@ impl Memory {
// Multi-byte reads use this helper to avoid charging each byte as a bus access.
fn read_byte(&self, address: u32) -> Result<u8, MemoryError> {
if self.cartridge_state().eeprom_mapped(address) {
return Err(MemoryError::UnsupportedCartridgeAccess {
address,
operation: "EEPROM non-halfword read",
});
}
if self.cartridge_state().flash_mapped(address)
&& self
.cpu_access
@ -990,7 +1001,7 @@ impl Memory {
},
);
let mut cartridge = self.cartridge_state();
cartridge.write(address, &bytes, &self.save_image)?;
cartridge.write(address, &bytes, &self.save_image, self.cpu_access.is_some())?;
if cartridge.mapped(address) {
if self.cartridge_step.get().is_some() {
self.cartridge_step.set(Some(cartridge));
@ -1224,7 +1235,7 @@ impl Memory {
self.write_index::<4>(address, self.write_access())?;
let bytes = value.to_le_bytes();
Self::validate_io_values(&mut audio, address, &bytes)?;
cartridge.write(address, &bytes, &self.save_image)?;
cartridge.write(address, &bytes, &self.save_image, self.cpu_access.is_some())?;
self.record_access(address, AccessWidth::Word);
if Serial::mapped(address) {
if let Some(mut step) = self.timer_step.get() {
@ -1255,6 +1266,9 @@ impl Memory {
if address & 1 != 0 {
return Err(MemoryError::Unaligned(address));
}
if self.cartridge_state().eeprom_mapped(address) {
return self.read_eeprom16(address);
}
self.validate_save_read_width(address)?;
self.record_access(address, AccessWidth::Halfword);
let value = u16::from_le_bytes([self.read_byte(address)?, self.read_byte(address + 1)?]);
@ -1263,8 +1277,26 @@ impl Memory {
Ok(value)
}
/// Shift out one EEPROM bit inside a machine step. Host reads outside a step only
/// inspect status or the next bit; nothing outside a step can stage the change.
fn read_eeprom16(&self, address: u32) -> Result<u16, MemoryError> {
self.record_access(address, AccessWidth::Halfword);
let mut cartridge = self.cartridge_state();
let value = cartridge.read_eeprom16(address, self.cpu_access.is_some())?;
if self.cartridge_step.get().is_some() {
self.cartridge_step.set(Some(cartridge));
}
Ok(value)
}
fn validate_save_read_width(&self, address: u32) -> Result<(), MemoryError> {
let cartridge = self.cartridge_state();
if cartridge.eeprom_mapped(address) {
return Err(MemoryError::UnsupportedCartridgeAccess {
address,
operation: "EEPROM non-halfword read",
});
}
if cartridge.save_mapped(address) {
return Err(MemoryError::UnsupportedCartridgeAccess {
address,