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bus/gameboy: Improved GBCHK003 notes.

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This commit is contained in:
Vas Crabb 2022-09-19 05:32:48 +10:00
parent 796d8d6720
commit e1e30896f5
1 changed files with 7 additions and 4 deletions
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11
src/devices/bus/gameboy/gbck003.cpp
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@ -11,7 +11,10 @@
The menu program sets up code in WRAM to switch to the selected game's ROM The menu program sets up code in WRAM to switch to the selected game's ROM
and exit configuration mode. The configuration values are read directly and exit configuration mode. The configuration values are read directly
from ROM, so the configuration is presumably applied when exiting from ROM, so the configuration is presumably applied when exiting
configuration mode. configuration mode. Leaving configuration mode presumably asserts the
reset line on the cartridge edge connector to get out of CGB mode for games
that expect DMG mode (e.g. Contra has all-black player sprites if the
system remains in CGB mode).
The write to 0x7B02 that presumably exits configuration mode is followed by The write to 0x7B02 that presumably exits configuration mode is followed by
code to do the following (SP contains 0xFFFE at this point): code to do the following (SP contains 0xFFFE at this point):
@ -22,9 +25,9 @@
* Jump to 0x0100 * Jump to 0x0100
This doesn't match the state set up by any official Nintendo bootstrap This doesn't match the state set up by any official Nintendo bootstrap
programs. Leaving configuration mode presumably asserts the rest line on programs. This code is probably left over from earlier multi-game
the cartridge edge connector to get out of CGB mode for games that expect cartridges that lacked CGB support and didn't reset the system when
DMG mode. starting a game.
0x0000-3FFF R - Low ROM bank. 0x0000-3FFF R - Low ROM bank.
0x4000-7FFF R - High ROM bank. 0x4000-7FFF R - High ROM bank.