From 5b4dbdc9a4a5eaf239ec2698afb2b62fd6659b1c Mon Sep 17 00:00:00 2001
From: Riyyi <riyyi3@gmail.com>
Date: Fri, 2 Sep 2022 22:38:02 +0200
Subject: [PATCH] Emulator: Add interrupt handling

---
 src/cpu.cpp | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/cpu.h   | 24 ++++++++++++++++++----
 2 files changed, 78 insertions(+), 4 deletions(-)

diff --git a/src/cpu.cpp b/src/cpu.cpp
index 51d12cd..3d14898 100644
--- a/src/cpu.cpp
+++ b/src/cpu.cpp
@@ -55,8 +55,66 @@ CPU::~CPU()
 
 // -----------------------------------------
 
+void CPU::handleInterrupt(uint32_t interrupt_flag, uint8_t interrupt_source, uint8_t address)
+{
+	// Clear interrupt
+	m_ime = 0;
+	Emu::the().writeMemory(0xff0f, interrupt_flag & (~interrupt_source));
+
+	// Call
+
+	m_wait_cycles += 20;
+
+	// Push address of the program counter on the stack, such that RET can pop it later
+	m_sp = (m_sp - 1) & 0xffff;
+	write(m_sp, m_pc >> 8); // msb(PC)
+	m_sp = (m_sp - 1) & 0xffff;
+	write(m_sp, m_pc & 0xff); // lsb(PC)
+
+	// Jump to address
+	m_pc = address;
+}
+
 void CPU::update()
 {
+	// -------------------------------------
+	// Interrupt Service Routine
+
+	bool effective_ime = m_ime;
+
+	// IME only becomes active after the instruction following EI
+	if (m_should_enable_ime) {
+		m_ime = 1;
+		m_should_enable_ime = 0;
+	}
+
+	if (effective_ime) {
+		// Get the 5 lower bits of the IE (interrupt enable) address
+		uint32_t interrupt_enabled = Emu::the().readMemory(0xffff) & 0x1f;
+		// Get the 5 lower bits of the IF (interrupt flag) address
+		uint32_t interrupt_flag = Emu::the().readMemory(0xff0f) & 0x1f;
+
+		uint32_t interrupt = interrupt_enabled & interrupt_flag;
+		if (interrupt & InterruptRequest::VBlank) {
+			handleInterrupt(interrupt_flag, InterruptRequest::VBlank, 0x40);
+		}
+		else if (interrupt & InterruptRequest::STAT) {
+			handleInterrupt(interrupt_flag, InterruptRequest::STAT, 0x48);
+		}
+		else if (interrupt & InterruptRequest::Timer) {
+			handleInterrupt(interrupt_flag, InterruptRequest::Timer, 0x50);
+		}
+		else if (interrupt & InterruptRequest::Serial) {
+			handleInterrupt(interrupt_flag, InterruptRequest::Serial, 0x58);
+		}
+		else if (interrupt & InterruptRequest::Joypad) {
+			handleInterrupt(interrupt_flag, InterruptRequest::Joypad, 0x60);
+		}
+	}
+
+	// -------------------------------------
+	// Run opcodes
+
 	m_wait_cycles--;
 	// TODO: convert to early-return
 	if (m_wait_cycles <= 0) {
diff --git a/src/cpu.h b/src/cpu.h
index d12a42a..146d586 100644
--- a/src/cpu.h
+++ b/src/cpu.h
@@ -13,6 +13,19 @@
 
 #include "processing-unit.h"
 #include "ruc/format/formatter.h"
+#include "ruc/meta/core.h"
+
+namespace InterruptRequest {
+
+enum Enum : uint8_t {
+	VBlank = BIT(0),
+	STAT = BIT(1),
+	Timer = BIT(2),
+	Serial = BIT(3),
+	Joypad = BIT(4),
+};
+
+} // namespace InterruptRequest
 
 class CPU final : public ProcessingUnit {
 private:
@@ -22,6 +35,7 @@ public:
 	explicit CPU(uint32_t frequency);
 	virtual ~CPU();
 
+	void handleInterrupt(uint32_t interrupt_flag, uint8_t interrupt_source, uint8_t address);
 	void update() override;
 
 	// -------------------------------------
@@ -147,11 +161,13 @@ private:
 	uint32_t m_sp { 0 }; // Stack Pointer
 
 	// Flags
-	uint32_t m_zf { 0 }; // Zero flag
-	uint32_t m_nf { 0 }; // Subtraction flag (BCD)
-	uint32_t m_hf { 0 }; // Half Carry flag (BCD)
-	uint32_t m_cf { 0 }; // Carry flag
+	uint32_t m_zf { 0 };  // Zero flag
+	uint32_t m_nf { 0 };  // Subtraction flag (BCD)
+	uint32_t m_hf { 0 };  // Half Carry flag (BCD)
+	uint32_t m_cf { 0 };  // Carry flag
+	uint32_t m_ime { 0 }; // Interrupt Master Enable flag
 
+	bool m_should_enable_ime { 0 };
 	int8_t m_wait_cycles { 0 };
 };