From 5bce4480db17fcb0a3a091a5ca2407c77fdbc596 Mon Sep 17 00:00:00 2001
From: Jeffrey Pfau <jeffrey@endrift.com>
Date: Fri, 15 Jan 2016 02:49:06 -0800
Subject: [PATCH] LR35902: Improve stalling behavior

---
 src/lr35902/isa-lr35902.c | 25 ++++++++-----------------
 src/lr35902/lr35902.c     |  6 +++++-
 src/lr35902/lr35902.h     |  1 +
 3 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/src/lr35902/isa-lr35902.c b/src/lr35902/isa-lr35902.c
index 6bbf1a6d1..8fbe076b5 100644
--- a/src/lr35902/isa-lr35902.c
+++ b/src/lr35902/isa-lr35902.c
@@ -27,8 +27,7 @@ DEFINE_INSTRUCTION_LR35902(JPFinish,
 	if (cpu->condition) {
 		cpu->pc = (cpu->bus << 8) | cpu->index;
 		cpu->memory.setActiveRegion(cpu, cpu->pc);
-		// TODO: Stall properly
-		cpu->cycles += 4;
+		cpu->executionState = LR35902_CORE_STALL;
 	})
 
 DEFINE_INSTRUCTION_LR35902(JPDelay,
@@ -48,8 +47,7 @@ DEFINE_INSTRUCTION_LR35902(JRFinish,
 	if (cpu->condition) {
 		cpu->pc += (int8_t) cpu->bus;
 		cpu->memory.setActiveRegion(cpu, cpu->pc);
-		// TODO: Stall properly
-		cpu->cycles += 4;
+		cpu->executionState = LR35902_CORE_STALL;
 	})
 
 #define DEFINE_JR_INSTRUCTION_LR35902(CONDITION_NAME, CONDITION) \
@@ -64,8 +62,7 @@ DEFINE_INSTRUCTION_LR35902(CALLFinish,
 	if (cpu->condition) {
 		cpu->pc = (cpu->bus << 8) | cpu->index;
 		cpu->memory.setActiveRegion(cpu, cpu->pc);
-		// TODO: Stall properly
-		cpu->cycles += 4;
+		cpu->executionState = LR35902_CORE_STALL;
 	})
 
 DEFINE_INSTRUCTION_LR35902(CALLUpdatePC,
@@ -103,8 +100,7 @@ DEFINE_INSTRUCTION_LR35902(RETUpdateSPL,
 	cpu->pc |= cpu->bus << 8;
 	cpu->sp += 2;
 	cpu->memory.setActiveRegion(cpu, cpu->pc);
-	// TODO: Stall properly
-	cpu->cycles += 4;)
+	cpu->executionState = LR35902_CORE_STALL;)
 
 DEFINE_INSTRUCTION_LR35902(RETUpdateSPH,
 	if (cpu->condition) {
@@ -368,14 +364,11 @@ DEFINE_INSTRUCTION_LR35902(LDIOA, \
 	DEFINE_INSTRUCTION_LR35902(INC ## REG, \
 		uint16_t reg = LR35902Read ## REG (cpu); \
 		LR35902Write ## REG (cpu, reg + 1); \
-		/* TODO: Stall properly */ \
-		cpu->cycles += 4;) \
+		cpu->executionState = LR35902_CORE_STALL;) \
 	DEFINE_INSTRUCTION_LR35902(DEC ## REG, \
 		uint16_t reg = LR35902Read ## REG (cpu); \
 		LR35902Write ## REG (cpu, reg - 1); \
-		/* TODO: Stall properly */ \
-		cpu->cycles += 4;) \
-
+		cpu->executionState = LR35902_CORE_STALL;)
 
 DEFINE_INCDEC_INSTRUCTION_LR35902(BC);
 DEFINE_INCDEC_INSTRUCTION_LR35902(DE);
@@ -383,13 +376,11 @@ DEFINE_INCDEC_INSTRUCTION_LR35902(HL);
 
 DEFINE_INSTRUCTION_LR35902(INCSP,
 	++cpu->sp;
-	// TODO: Stall properly
-	cpu->cycles += 4;)
+	cpu->executionState = LR35902_CORE_STALL;)
 
 DEFINE_INSTRUCTION_LR35902(DECSP,
 	--cpu->sp;
-	// TODO: Stall properly
-	cpu->cycles += 4;)
+	cpu->executionState = LR35902_CORE_STALL;)
 
 DEFINE_INSTRUCTION_LR35902(DI, cpu->irqh.setInterrupts(cpu, false));
 DEFINE_INSTRUCTION_LR35902(EI, cpu->irqh.setInterrupts(cpu, true));
diff --git a/src/lr35902/lr35902.c b/src/lr35902/lr35902.c
index 99701188a..c3e0615f5 100644
--- a/src/lr35902/lr35902.c
+++ b/src/lr35902/lr35902.c
@@ -85,7 +85,8 @@ void LR35902Tick(struct LR35902Core* cpu) {
 			cpu->pc = cpu->irqVector;
 			cpu->irqPending = false;
 			cpu->irqh.setInterrupts(cpu, false);
-			// TODO: stall
+			cpu->instruction = _lr35902InstructionTable[0]; // NOP
+			break;
 		}
 		cpu->bus = cpu->memory.load8(cpu, cpu->pc);
 		cpu->instruction = _lr35902InstructionTable[cpu->bus];
@@ -104,6 +105,9 @@ void LR35902Tick(struct LR35902Core* cpu) {
 		cpu->bus = cpu->memory.load8(cpu, cpu->pc);
 		++cpu->pc;
 		break;
+	case LR35902_CORE_STALL:
+		cpu->instruction = _lr35902InstructionTable[0]; // NOP
+		break;
 	default:
 		break;
 	}
diff --git a/src/lr35902/lr35902.h b/src/lr35902/lr35902.h
index 74fd12801..7d25f45fe 100644
--- a/src/lr35902/lr35902.h
+++ b/src/lr35902/lr35902.h
@@ -43,6 +43,7 @@ enum LR35902ExecutionState {
 	LR35902_CORE_MEMORY_LOAD = 4,
 	LR35902_CORE_MEMORY_STORE = 8,
 	LR35902_CORE_READ_PC = 12,
+	LR35902_CORE_STALL = 16
 };
 
 struct LR35902Memory {