0xrsydn/gameboy-rust
1
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

fix(memory): ignore CPU and DMA writes to the Game Pak ROM windows

Browse source 
Stores to 0x08-0x0c returned ReadOnly and stopped the machine. Hardware ignores
them, and a second game's boot code stores to a ROM mirror. Emulated writes now
pay their bus cost and change nothing. The 0x0d window stays a diagnostic until
EEPROM is modeled there, and host writes stay strict.

Tests that used a ROM store as their failing write now cross an ignored ROM
word into the 0x0d window.

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 08:26:03 +07:00
commit 258fbff2fa
25 changed files with 86 additions and 74 deletions
Download patch file Download diff file Expand all files Collapse all files

4
docs/hardware/cartridge-gpio.md
View file

@ -52,9 +52,9 @@ Byte writes are diagnostic because the consulted bus-width description is uncert
Byte, halfword, and word reads use ordinary little-endian lanes, including register/ROM boundaries.
Only the documented first-window addresses are implemented.
Other ROM windows still expose supplied ROM bytes; their writes remain read-only diagnostics.
Other ROM windows still expose supplied ROM bytes; CPU and DMA writes there are ignored like other ROM writes.
GPIO mirroring and writes at alias addresses have not been independently validated.
Without explicit hardware selection, all these addresses remain ordinary read-only cartridge memory.
Without explicit hardware selection, all these addresses remain ordinary read-only cartridge memory, so CPU and DMA writes are ignored.
## RTC command and control transfers