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CPU (THUMB): fix for opcode 'BX PC' which does switch to ARM state. 

This fix allows the BIOS to boot a bit further (still doesn't boot).
This commit is contained in:
luigi__ 2009-08-02 11:21:50 +00:00
parent 573f321508
commit a10305e786
1 changed files with 16 additions and 5 deletions
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11
desmume/src/thumb_instructions.cpp
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@ -540,11 +540,22 @@ TEMPLATE static u32 FASTCALL OP_MOV_SPE()
TEMPLATE static u32 FASTCALL OP_BX_THUMB() TEMPLATE static u32 FASTCALL OP_BX_THUMB()
{ {
// When using PC as operand with BX opcode, switch to ARM state and jump to (instruct_adr+4)
// Reference: http://nocash.emubase.de/gbatek.htm#thumb5hiregisteroperationsbranchexchange
if (REG_POS(cpu->instruction, 3) == 15)
{
cpu->CPSR.bits.T = 0;
cpu->R[15] &= 0xFFFFFFFC;
cpu->next_instruction = cpu->R[15];
}
else
{
u32 Rm = cpu->R[REG_POS(cpu->instruction, 3)]; u32 Rm = cpu->R[REG_POS(cpu->instruction, 3)];
cpu->CPSR.bits.T = BIT0(Rm); cpu->CPSR.bits.T = BIT0(Rm);
cpu->R[15] = (Rm & 0xFFFFFFFE); cpu->R[15] = (Rm & 0xFFFFFFFE);
cpu->next_instruction = cpu->R[15]; cpu->next_instruction = cpu->R[15];
}
return 3; return 3;
} }