GBC: Hopefully improved interrupt accuracy in regards to cpu HALT

This fixes Link's Awakening, more testing needed to see if it breaks others

Author: ducalex

gnuboy-go/components/gnuboy/cpu.c

@@ -310,8 +310,8 @@ static inline void timer_advance(int cycles)
 			cpu.timer &= 0x1ff;
 			if (tima >= 256)
 			{
-				hw_interrupt(IF_TIMER, IF_TIMER);
-				hw_interrupt(0, IF_TIMER);
+				hw_interrupt(IF_TIMER, 1);
+				hw_interrupt(IF_TIMER, 0);
 				tima = R_TMA;
 			}
 			R_TIMA = tima;
@@ -330,8 +330,8 @@ static inline void serial_advance(int cycles)
 			R_SB = 0xFF;
 			R_SC &= 0x7f;
 			hw.serial = 0;
-			hw_interrupt(IF_SERIAL, IF_SERIAL);
-			hw_interrupt(0, IF_SERIAL);
+			hw_interrupt(IF_SERIAL, 1);
+			hw_interrupt(IF_SERIAL, 0);
 		}
 	}
 }
@@ -836,7 +836,11 @@ int cpu_emulate(int cycles)
 		break;
 
 	case 0x76: /* HALT */
-		cpu.halted = 1;
+		if (IME) {
+			cpu.halted = 1;
+		} else {
+			printf("FIX ME: HALT requested with IME = 0\n");
+		}
 		break;
 
 	case 0xCB: /* CB prefix */

gnuboy-go/components/gnuboy/hw.c

@@ -12,22 +12,28 @@ hw_t hw;
 
 
 /*
- * hw_interrupt changes the virtual interrupt lines included in the
- * specified mask to the values the corresponding bits in i take, and
- * in doing so, raises the appropriate bit of R_IF for any interrupt
- * lines that transition from low to high.
+ * hw_interrupt changes the virtual interrupt line(s) defined by i
+ * The interrupt fires (added to R_IF) when the line transitions from 0 to 1.
+ * It does not refire if the line was already high.
  */
-void hw_interrupt(byte i, byte mask)
+void hw_interrupt(byte i, int level)
 {
-	i &= mask;
-	R_IF |= i & (hw.ilines ^ i);
-	if (i) {
-		// HALT shouldn't even be entered when interrupts are disabled.
-		// No need to check for IME, and it works around a stall bug.
-		cpu.halted = 0;
+	if (level == 0)
+	{
+		hw.ilines &= ~i;
+	}
+	else if ((hw.ilines & i) == 0)
+	{
+		hw.ilines |= i;
+		R_IF |= i; // Fire!
+
+		if ((R_IE & i) != 0)
+		{
+			// Wake up the CPU when an enabled interrupt occurs
+			// IME doesn't matter at this point, only IE
+			cpu.halted = 0;
+		}
 	}
-	hw.ilines &= ~mask;
-	hw.ilines |= i;
 }
 
 
@@ -104,26 +110,30 @@ void IRAM_ATTR pad_refresh()
 	R_P1 ^= 0x0F;
 	if (oldp1 & ~R_P1 & 0x0F)
 	{
-		hw_interrupt(IF_PAD, IF_PAD);
-		hw_interrupt(0, IF_PAD);
+		hw_interrupt(IF_PAD, 1);
+		hw_interrupt(IF_PAD, 0);
 	}
 }
 
 
 /*
- * These simple functions just update the state of a button on the
- * pad.
+ * pad_set updates the state of one or more buttons on the pad and calls
+ * pad_refresh() to fire an interrupt if the pad changed.
  */
-void IRAM_ATTR pad_set(byte k, int st)
+void IRAM_ATTR pad_set(byte btn, int set)
 {
-	if (st) {
-		if (hw.pad & k) return;
-		hw.pad |= k;
-	} else {
-		if (!(hw.pad & k)) return;
-		hw.pad &= ~k;
+	int new_pad = hw.pad;
+
+	if (set)
+		new_pad |= btn;
+	else
+		new_pad &= ~btn;
+
+	if (hw.pad != new_pad)
+	{
+		hw.pad = new_pad;
+		pad_refresh();
 	}
-	pad_refresh();
 }
 
 void hw_reset()

gnuboy-go/components/gnuboy/hw.h

@@ -37,8 +37,8 @@ void hw_hdma();
 void hw_dma(byte b);
 void hw_hdma_cmd(byte c);
 void hw_reset();
-void pad_set(byte k, int st);
+void pad_set(byte btn, int set);
 void pad_refresh();
-void hw_interrupt(byte i, byte mask);
+void hw_interrupt(byte i, int level);
 
 #endif

gnuboy-go/components/gnuboy/lcd.c

@@ -707,20 +707,20 @@ void pal_dirty()
 void stat_trigger()
 {
 	const byte condbits[4] = { 0x08, 0x10, 0x20, 0x00 };
-	byte flag = 0;
+	int level = 0;
 
 	if (R_LY == R_LYC)
 	{
 		R_STAT |= 0x04;
-		if (R_STAT & 0x40) flag = IF_STAT;
+		if (R_STAT & 0x40) level = 1;
 	}
 	else R_STAT &= ~0x04;
 
-	if (R_STAT & condbits[R_STAT&3]) flag = IF_STAT;
+	if (R_STAT & condbits[R_STAT&3]) level = 1;
 
-	if (!(R_LCDC & 0x80)) flag = 0;
+	if (!(R_LCDC & 0x80)) level = 0;
 
-	hw_interrupt(flag, IF_STAT);
+	hw_interrupt(IF_STAT, level);
 }
 
 
@@ -736,8 +736,7 @@ static void inline stat_change(int stat)
 	stat &= 3;
 	R_STAT = (R_STAT & 0x7C) | stat;
 
-	if (stat != 1) hw_interrupt(0, IF_VBLANK);
-	/* hw_interrupt((stat == 1) ? IF_VBLANK : 0, IF_VBLANK); */
+	if (stat != 1) hw_interrupt(IF_VBLANK, 0);
 	stat_trigger();
 }
 
@@ -834,7 +833,7 @@ void lcd_emulate()
 				before interrupt is triggered */
 				if (cpu.halted)
 				{
-					hw_interrupt(IF_VBLANK, IF_VBLANK);
+					hw_interrupt(IF_VBLANK, 1);
 					CYCLES += 228;
 				}
 				else CYCLES += 10;
@@ -844,7 +843,7 @@ void lcd_emulate()
 
 			// Hack for Worms Armageddon
 			if (R_STAT == 0x48)
-				hw_interrupt(0, IF_STAT);
+				hw_interrupt(IF_STAT, 0);
 
 			stat_change(2); /* -> search */
 			CYCLES += 40;
@@ -853,7 +852,7 @@ void lcd_emulate()
 			/* vblank -> */
 			if (!(hw.ilines & IF_VBLANK))
 			{
-				hw_interrupt(IF_VBLANK, IF_VBLANK);
+				hw_interrupt(IF_VBLANK, 1);
 				CYCLES += 218;
 				break;
 			}

gnuboy-go/components/gnuboy/mem.c

@@ -158,7 +158,7 @@ static inline void ioreg_write(byte r, byte b)
 	case RI_STAT:
 		R_STAT = (R_STAT & 0x07) | (b & 0x78);
 		if (!hw.cgb && !(R_STAT & 2)) /* DMG STAT write bug => interrupt */
-			hw_interrupt(IF_STAT, IF_STAT);
+			hw_interrupt(IF_STAT, 1);
 		stat_trigger();
 		break;
 	case RI_LYC: