Implement interrupt polling

Enough to pass EI & DI tests in Blargg's interrupts ROM
maxfierke · Jan 7, 2024 · 86f9e12 · 86f9e12
1 parent 9c994f6
commit 86f9e12
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Showing 5 changed files with 96 additions and 13 deletions.
diff --git a/cpu/cpu.go b/cpu/cpu.go
@@ -5,6 +5,7 @@ import (
 	"math/bits"
 
 	"github.com/maxfierke/gogo-gb/cpu/isa"
+	"github.com/maxfierke/gogo-gb/devices"
 	"github.com/maxfierke/gogo-gb/mem"
 )
 
@@ -1703,6 +1704,38 @@ func (cpu *CPU) Execute(mmu *mem.MMU, inst *isa.Instruction) (nextPC uint16, cyc
 	return cpu.PC.Read() + uint16(opcode.Bytes), uint8(opcode.Cycles[0]), nil
 }
 
+func (cpu *CPU) PollInterrupts(mmu *mem.MMU, ic *devices.InterruptController) uint8 {
+	if cpu.ime {
+		interrupt := ic.ConsumeRequest()
+		if interrupt == devices.INT_NONE {
+			return 0
+		}
+
+		// Disable interrupts while we process this one
+		cpu.ime = false
+
+		// Jump to interrupt handler
+		cpu.push(mmu, cpu.PC.Read())
+		cpu.PC.Write(uint16(interrupt))
+
+		// If we were halted, we're not now!
+		cpu.halted = false
+
+		// Consuming an IRQ is 16 cycles
+		return 16
+	} else if cpu.halted {
+		if interrupt := ic.NextRequest(); interrupt != 0 {
+			// Wakey-wakey
+			cpu.halted = false
+		}
+
+		return 0
+	} else {
+		// Ignore
+		return 0
+	}
+}
+
 func (cpu *CPU) Reset() {
 	cpu.Reg.Reset()
 	cpu.PC.Write(0x0000)

diff --git a/debug/debugger.go b/debug/debugger.go
@@ -11,6 +11,7 @@ type Debugger interface {
 	Setup(cpu *cpu.CPU, mmu *mem.MMU)
 	OnDecode(cpu *cpu.CPU, mmu *mem.MMU)
 	OnExecute(cpu *cpu.CPU, mmu *mem.MMU)
+	OnInterrupt(cpu *cpu.CPU, mmu *mem.MMU)
 	OnRead(mmu *mem.MMU, addr uint16) mem.MemRead
 	OnWrite(mmu *mem.MMU, addr uint16, value byte) mem.MemWrite
 }
@@ -32,9 +33,10 @@ func NewNullDebugger() *NullDebugger {
 	return &NullDebugger{}
 }
 
-func (nd *NullDebugger) Setup(cpu *cpu.CPU, mmu *mem.MMU)     {}
-func (nd *NullDebugger) OnDecode(cpu *cpu.CPU, mmu *mem.MMU)  {}
-func (nd *NullDebugger) OnExecute(cpu *cpu.CPU, mmu *mem.MMU) {}
+func (nd *NullDebugger) Setup(cpu *cpu.CPU, mmu *mem.MMU)       {}
+func (nd *NullDebugger) OnDecode(cpu *cpu.CPU, mmu *mem.MMU)    {}
+func (nd *NullDebugger) OnExecute(cpu *cpu.CPU, mmu *mem.MMU)   {}
+func (nd *NullDebugger) OnInterrupt(cpu *cpu.CPU, mmu *mem.MMU) {}
 
 func (nd *NullDebugger) OnRead(mmu *mem.MMU, addr uint16) mem.MemRead {
 	return mem.ReadPassthrough()

diff --git a/debug/gb_doctor.go b/debug/gb_doctor.go
@@ -25,6 +25,8 @@ func (gbd *GBDoctorDebugger) OnExecute(cpu *cpu.CPU, mmu *mem.MMU) {
 	gbd.printState(cpu, mmu)
 }
 
+func (gbd *GBDoctorDebugger) OnInterrupt(cpu *cpu.CPU, mmu *mem.MMU) {}
+
 func (gbd *GBDoctorDebugger) OnRead(mmu *mem.MMU, addr uint16) mem.MemRead {
 	if addr == devices.REG_LCD_LY {
 		return mem.ReadReplace(0x90) // gameboy-doctor needs a stubbed out LCD

diff --git a/devices/interrupts.go b/devices/interrupts.go
@@ -9,6 +9,7 @@ import (
 const (
 	REG_IE     = 0xFFFF
 	REG_IF     = 0xFF0F
+	INT_NONE   = 0x00
 	INT_VBLANK = 0x40
 	INT_STAT   = 0x48
 	INT_TIMER  = 0x50
@@ -92,22 +93,63 @@ func NewInterruptController() *InterruptController {
 	}
 }
 
-func (ic *InterruptController) Reset() {
-	ic.enabled.Write(0x00)
-	ic.requested.Write(0x00)
-}
+func (ic *InterruptController) ConsumeRequest() byte {
+	nextReq := ic.NextRequest()
 
-func (ic *InterruptController) RequestSerial() {
-	ic.requested.serial = true
+	if nextReq == INT_VBLANK {
+		ic.requested.vblank = false
+	}
+
+	if nextReq == INT_STAT {
+		ic.requested.lcd = false
+	}
+
+	if nextReq == INT_JOYPAD {
+		ic.requested.joypad = false
+	}
+
+	if nextReq == INT_SERIAL {
+		ic.requested.serial = false
+	}
+
+	if nextReq == INT_TIMER {
+		ic.requested.timer = false
+	}
+
+	return nextReq
 }
 
-func (ic *InterruptController) ConsumeSerial() byte {
+func (ic *InterruptController) NextRequest() byte {
+	if ic.enabled.vblank && ic.requested.vblank {
+		return INT_VBLANK
+	}
+
+	if ic.enabled.lcd && ic.requested.lcd {
+		return INT_STAT
+	}
+
+	if ic.enabled.timer && ic.requested.timer {
+		return INT_TIMER
+	}
+
 	if ic.enabled.serial && ic.requested.serial {
-		ic.requested.serial = false
 		return INT_SERIAL
 	}
 
-	return 0
+	if ic.enabled.joypad && ic.requested.joypad {
+		return INT_JOYPAD
+	}
+
+	return INT_NONE
+}
+
+func (ic *InterruptController) Reset() {
+	ic.enabled.Write(0x00)
+	ic.requested.Write(0x00)
+}
+
+func (ic *InterruptController) RequestSerial() {
+	ic.requested.serial = true
 }
 
 func (ic *InterruptController) OnRead(mmu *mem.MMU, addr uint16) mem.MemRead {

diff --git a/hardware/dmg.go b/hardware/dmg.go
@@ -79,12 +79,16 @@ func (dmg *DMG) DebugPrint() {
 func (dmg *DMG) Step() bool {
 	dmg.debugger.OnDecode(dmg.cpu, dmg.mmu)
 
-	_, err := dmg.cpu.Step(dmg.mmu)
+	cycles, err := dmg.cpu.Step(dmg.mmu)
 	if err != nil {
 		dmg.logger.Printf("Unexpected error while executing instruction: %v\n", err)
 		return false
 	}
 
+	cycles += dmg.cpu.PollInterrupts(dmg.mmu, dmg.ic)
+
+	dmg.serial.Step(uint(cycles), dmg.ic)
+
 	return true
 }