From e224b455761b32263deeb36821f8091fadc63399 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Mon, 6 Dec 2021 03:27:35 -0800
Subject: [PATCH] GBA: Correct key IRQ edge behavior

---
 src/gba/core.c |  1 +
 src/gba/gba.c  | 25 ++++++++++++-------------
 src/gba/io.c   |  3 +++
 3 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/src/gba/core.c b/src/gba/core.c
index f186d130a..1d0292f4a 100644
--- a/src/gba/core.c
+++ b/src/gba/core.c
@@ -709,6 +709,7 @@ static void _GBACoreAddKeys(struct mCore* core, uint32_t keys) {
 static void _GBACoreClearKeys(struct mCore* core, uint32_t keys) {
 	struct GBA* gba = core->board;
 	gba->keysActive &= ~keys;
+	GBATestKeypadIRQ(gba);
 }
 
 static int32_t _GBACoreFrameCounter(const struct mCore* core) {
diff --git a/src/gba/gba.c b/src/gba/gba.c
index 6df5086a1..16d02fd2c 100644
--- a/src/gba/gba.c
+++ b/src/gba/gba.c
@@ -91,7 +91,7 @@ static void GBAInit(void* cpu, struct mCPUComponent* component) {
 	GBAHardwareInit(&gba->memory.hw, NULL);
 
 	gba->keysActive = 0;
-	gba->keysLast = 0;
+	gba->keysLast = 0x400;
 	gba->rotationSource = 0;
 	gba->luminanceSource = 0;
 	gba->rtcSource = 0;
@@ -878,27 +878,26 @@ void GBAFrameEnded(struct GBA* gba) {
 }
 
 void GBATestKeypadIRQ(struct GBA* gba) {
-	if (gba->keysActive == gba->keysLast) {
-		return;
-	}
+	uint16_t keysLast = gba->keysLast;
+	uint16_t keysActive = gba->keysActive;
+
 	uint16_t keycnt = gba->memory.io[REG_KEYCNT >> 1];
 	if (!(keycnt & 0x4000)) {
 		return;
 	}
+	gba->keysLast = keysActive;
 	int isAnd = keycnt & 0x8000;
 
 	keycnt &= 0x3FF;
-	uint16_t keyInput = gba->keysActive & keycnt;
-	uint16_t lastInput = gba->keysLast & keycnt;
-	gba->keysLast = gba->keysActive;
-	if (keyInput == lastInput) {
-		return;
-	}
-
-	if (isAnd && keycnt == keyInput) {
+	if (isAnd && keycnt == (keysActive & keycnt)) {
+		if (keysLast == keysActive) {
+			return;
+		}
 		GBARaiseIRQ(gba, IRQ_KEYPAD, 0);
-	} else if (!isAnd && keyInput) {
+	} else if (!isAnd && (keysActive & keycnt)) {
 		GBARaiseIRQ(gba, IRQ_KEYPAD, 0);
+	} else {
+		gba->keysLast = 0x400;
 	}
 }
 
diff --git a/src/gba/io.c b/src/gba/io.c
index 5c90f946a..8c6bbb5ad 100644
--- a/src/gba/io.c
+++ b/src/gba/io.c
@@ -547,6 +547,9 @@ void GBAIOWrite(struct GBA* gba, uint32_t address, uint16_t value) {
 	// Interrupts and misc
 	case REG_KEYCNT:
 		value &= 0xC3FF;
+		if (gba->keysLast < 0x400) {
+			gba->keysLast &= gba->memory.io[address >> 1] | ~value;
+		}
 		gba->memory.io[address >> 1] = value;
 		GBATestKeypadIRQ(gba);
 		return;