Correct read emulation of the BANK register while still in the boot ROM

LIJI32 · Jul 29, 2023 · 4ab256d · 4ab256d
1 parent 10d9963
commit 4ab256d
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Showing 2 changed files with 4 additions and 3 deletions.
diff --git a/Core/gb.h b/Core/gb.h
@@ -192,7 +192,7 @@ enum {
     /* Missing */
 
     GB_IO_VBK        = 0x4F, // CGB Mode Only - VRAM Bank
-    GB_IO_BANK       = 0x50, // Write to disable the BIOS mapping
+    GB_IO_BANK       = 0x50, // Write to disable the boot ROM mapping
 
     /* CGB DMA */
     GB_IO_HDMA1      = 0x51, // CGB Mode Only - New DMA Source, High

diff --git a/Core/memory.c b/Core/memory.c
@@ -702,7 +702,8 @@ static uint8_t read_high_memory(GB_gameboy_t *gb, uint16_t addr)
                     return 0xFF;
                 }
                 return (gb->io_registers[GB_IO_KEY1] & 0x7F) | (gb->cgb_double_speed? 0xFE : 0x7E);
-
+            case GB_IO_BANK:
+                return 0xFE | gb->boot_rom_finished;
             case GB_IO_RP: {
                 if (!gb->cgb_mode) return 0xFF;
                 /* You will read your own IR LED if it's on. */
@@ -1572,7 +1573,7 @@ static void write_high_memory(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
                 return;
 
             case GB_IO_BANK:
-                gb->boot_rom_finished = true;
+                gb->boot_rom_finished |= value & 1;
                 return;
 
             case GB_IO_KEY0: