cpu - Fix timing of delay when enabling interrupts
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1194340657
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002b745917
2 changed files with 12 additions and 3 deletions
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@ -191,8 +191,6 @@ void Cpu::handleInterrupts()
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u8 si = state.IE & state.IF & INT_MASK;
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if (state.IME == IME_SCHEDULED)
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state.IME = IME_DELAYED;
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else if (state.IME == IME_DELAYED)
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state.IME = IME_ON;
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else if (state.IME == IME_ON && si != 0)
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{
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13
cpu/cpu.h
13
cpu/cpu.h
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@ -43,11 +43,22 @@ enum InterruptType : u8
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INT_MASK = 0x1F,
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};
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/**
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IME - Interrupt Master Enable
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An EI instruction will enable the interrupts, but delayed. During the next instruction after EI,
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interrupts are still disabled. For this to be emulated we use a small state machine. which works as follows
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instruction EI - sets IME_SCHEDULED
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handleInterrupts -> IME_SCHEDULED to IME_ON (but no call to isr yet)
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instruction any - is IME_ON, but no chance for call to isr yet
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handleInterrupts -> is IME_ON, do a call to isr if necessary
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*/
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enum IME_state
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{
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IME_OFF,
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IME_SCHEDULED,
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IME_DELAYED,
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IME_ON,
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};
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