Struct GsuMem 

pub struct GsuMem<'a> {
    pub rom: &'a [u8],
    pub rom_mask: u32,
    pub ram: &'a mut [u8],
    pub ram_mask: u32,
}

The Game Pak ROM/RAM the GSU reads and plots into, with the GSU-internal 24-bit decode.

The board constructs this each run, borrowing its ROM (shared, read-only) and its Game Pak RAM (the plot target). The address map is the GSU’s own view (ares SuperFX::read/write): banks $00-$3F fold LoROM-style, $40-$5F are linear ROM, $70-$71 are the RAM bitmap.

Fields

rom: &'a [u8]

Game Pak ROM image (already mirror-rounded to a power-of-two rom_mask + 1).

rom_mask: u32

rom.len().next_power_of_two() - 1 (ares romSizeRound(rom.size()) - 1).

ram: &'a mut [u8]

Game Pak RAM (the GSU plot bitmap), ram_mask + 1 bytes.

ram_mask: u32

ram.len() - 1 (RAM is always a power of two).