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gba: the open BIOS's Div returns |quotient| in r3 (Minish Cap's file select) #10

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Merged
finger563 merged 1 commit into from
Oct 24, 2026
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gba: the open BIOS's Div returns |quotient| in r3 (Minish Cap's file select) #10

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10 changes: 9 additions & 1 deletion components/gba/gpsp/open_gba_bios.c
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Original file line number Diff line number Diff line change
@@ -1,4 +1,12 @@
// generated from bios/open_gba_bios.bin (gpSP's open-source BIOS replacement)
// with one patch (tab5-emu): Div / DivArm return |quotient| in r3, as the
// real BIOS does. swi_Div computes it (`mov r3, r2` at 0x17F0), but the SWI
// dispatcher restores the caller's r2 / r3 from the stack on the way out
// (swi_complete: ldmfd sp!, {r2, r3, lr}), so the value never came back.
// The instruction now stores it into that saved r3 slot instead
// (`str r2, [sp, #4]`, 0xE58D2004), which the dispatcher then returns.
// The Legend of Zelda: The Minish Cap reads it: without it the file select
// screen stays half slid in, with no file slots and no language menu.
#include <stdint.h>
const uint8_t open_gba_bios_rom[16384] = {
0x0c,0x00,0x00,0xea,0x15,0x00,0x00,0xea,0x15,0x00,0x00,0xea,0x13,0x00,0x00,0xea,
Expand Down Expand Up @@ -384,7 +392,7 @@ const uint8_t open_gba_bios_rom[16384] = {
0x01,0x30,0xa0,0xe3,0x00,0x00,0x51,0xe1,0x81,0x10,0xa0,0x91,0x83,0x30,0xa0,0x91,
0xfb,0xff,0xff,0x9a,0x01,0x00,0x50,0xe1,0x01,0x00,0x40,0x20,0x03,0x20,0x82,0x21,
0xa3,0x30,0xb0,0xe1,0xa1,0x10,0xa0,0x31,0xf9,0xff,0xff,0x3a,0x00,0x10,0xa0,0xe1,
0x02,0x30,0xa0,0xe1,0x02,0x00,0xa0,0xe1,0x02,0x01,0x1c,0xe3,0x00,0x00,0x60,0x42,
0x04,0x20,0x8d,0xe5,0x02,0x00,0xa0,0xe1,0x02,0x01,0x1c,0xe3,0x00,0x00,0x60,0x42,
0x1e,0xff,0x2f,0xe1,0x01,0x33,0xa0,0xe3,0x06,0x20,0x53,0xe5,0x07,0x00,0x00,0xeb,
0x00,0x00,0x52,0xe3,0xff,0x1f,0x13,0xe9,0x02,0xe4,0xa0,0x13,0x02,0xe3,0xa0,0x03,
0x1f,0x00,0xa0,0xe3,0x00,0xf0,0x29,0xe1,0x00,0x00,0xa0,0xe3,0x1e,0xff,0x2f,0xe1,
Expand Down
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