Crate pak 

Available on crate feature pak only.

The Game Pak’s own hardware.

The memory bank controller answers writes to the ROM address range as register writes, and one 8 KiB window at 0xA000..=0xBFFF shows whatever those registers last selected. For example SRAM, where a game saves its data.

Sharing the window

Every peripheral here shares that window, and selecting one deselects the rest, so they do not nest:

// Wrong: the second read comes from the rtc.
FILE.open(cs, |f| {
    let a = f.gold.get();
    let t = rtc::time(cs);   // selects rtc registers
    let b = f.gold.get();    // reads the rtc, not the save
});

An interrupt handler nests the same way without the code showing it, and one racing a scope for the same bytes would be a data race. Sram::open takes a CriticalSection to rule that out, from gb::interrupt::free or critical_section::with. The rest only write registers, and the rule above is all that keeps a handler off them.

What a cartridge has

cargo-gb derives the capabilities below from cartridge_type and ram_size in header.toml, so a program that reaches for hardware the cartridge lacks fails to compile rather than writing to a chip that is not there.

MBC1 spends the same two register bits on ROM banks above 512 KiB and on SRAM banks, so wide_banks and more than one SRAM bank cannot both be set.

Module	Needs	Present on
sram	ram_size above zero	MBC1, MBC3, MBC5
rtc	+TIMER	MBC3
rumble	+RUMBLE	MBC5
tilt, eeprom	MBC7	MBC7

Modules

eepromgb_pak_tilt

MBC7’s save storage: 128 words on a serial EEPROM.

rtcgb_pak_rtc

The MBC3 clock: seconds to days, running on the cartridge battery.

rumblegb_pak_rumble

The MBC5 rumble motor.

sram

The cartridge’s own RAM, usually kept alive by a battery.

tiltgb_pak_tilt

The MBC7 accelerometer.

Structs

CriticalSection

Critical section token.

Attribute Macros

sram

Place a value at the base of an SRAM bank.