FDS: Adjust to transfer flag timing

- Disk transfer flag (bit 1 or register read $4030) is not set
  independently from the disk irq state. Transfer flag is automatically
  enabled when DiskSeekIRQ decrements to zero, meaning  byte transfer is
  done and does not wait for disk irq. Flag is reset after serviced in
  $4030, $4031, $4024. (fix Putt Putt Golf)

Author: negativeExponent

src/fds.c

@@ -102,6 +102,7 @@ static uint16 mapperFDS_blocklen;   /* length of current block */
 static uint16 mapperFDS_diskaddr;   /* current address relative to blockstart */
 static uint8 mapperFDS_diskaccess;  /* disk needs to be accessed at least once
                                        before writing */
+static uint8 mapperFDS_transferflag;
 
 #define BYTES_PER_SIDE 65500
 
@@ -154,8 +155,24 @@ static void FDSPower(void) {
 	MapIRQHook = FDSFix;
 	GameStateRestore = FDSStateRestore;
 
-	SetReadHandler(0x4020, 0x5FFF, FDSRead);
-	SetWriteHandler(0x4020, 0x5FFF, FDSWrite);
+	SetReadHandler(0x4030, 0x4033, FDSRead);
+	SetWriteHandler(0x4020, 0x4025, FDSWrite);
+
+	SetReadHandler(0x4040, 0x407F, FDSWaveRead);
+	SetReadHandler(0x4090, 0x4090, FDSEnvVolumeRead);
+	SetReadHandler(0x4092, 0x4092, FDSEnvModRead);
+
+	SetWriteHandler(0x4040, 0x407F, FDSWaveWrite);
+	SetWriteHandler(0x4080, 0x4080, FDSSReg0Write);
+	SetWriteHandler(0x4082, 0x4082, FDSSReg1Write);
+	SetWriteHandler(0x4083, 0x4083, FDSSReg2Write);
+	SetWriteHandler(0x4084, 0x4084, FDSSReg3Write);
+	SetWriteHandler(0x4085, 0x4085, FDSSReg4Write);
+	SetWriteHandler(0x4086, 0x4086, FDSSReg5Write);
+	SetWriteHandler(0x4087, 0x4087, FDSSReg6Write);
+	SetWriteHandler(0x4088, 0x4088, FDSSReg7Write);
+	SetWriteHandler(0x4089, 0x4089, FDSSReg8Write);
+	SetWriteHandler(0x408A, 0x408A, FDSSReg9Write);
 
 	SetWriteHandler(0x6000, 0xDFFF, CartBW);
 	SetReadHandler(0x6000, 0xFFFF, CartBR);
@@ -176,6 +193,7 @@ static void FDSPower(void) {
 	mapperFDS_blocklen = 0;
 	mapperFDS_diskaddr = 0;
 	mapperFDS_diskaccess = 0;
+	mapperFDS_transferflag = FALSE;
 }
 
 static uint8 isDiskInserted(void) {
@@ -238,6 +256,7 @@ static void FDSFix(int a) {
 	if (DiskSeekIRQ > 0) {
 		DiskSeekIRQ -= a;
 		if (DiskSeekIRQ <= 0) {
+			mapperFDS_transferflag = TRUE;
 			if (mapperFDS_control & 0x80) {
 				X6502_IRQBegin(FCEU_IQEXT2);
 			}
@@ -246,91 +265,66 @@ static void FDSFix(int a) {
 }
 
 static DECLFR(FDSRead) {
-	uint8 ret = 0;
+	uint8 ret = cpu.openbus;
 
 	if (!DiskIOEnabled) {
 		return ret;
 	}
 
-	if ((A >= 0x4040) && (A <= 0x407F)) {
-		return FDSWaveRead(A);
-	}
-
 	switch (A) {
 	case 0x4030:
-		ret = 0x80;
-
-		/* Cheap hack. */
-		if (cpu.IRQlow & FCEU_IQEXT) {
-			ret |= 1;
-		}
-		if (cpu.IRQlow & FCEU_IQEXT2) {
-			ret |= 2;
-		}
-#ifdef FCEUDEF_DEBUGGER
-		if (!fceuindbg)
-#endif
-		{
-			X6502_IRQEnd(FCEU_IQEXT);
-			X6502_IRQEnd(FCEU_IQEXT2);
-		}
+		ret &= 0x2C;
+		ret |= (cpu.IRQlow & FCEU_IQEXT) ? 0x01 : 0;
+		ret |= mapperFDS_transferflag ? 0x02 : 0;
+		ret |= 0x80; /* disk is readable/writeable */
+		X6502_IRQEnd(FCEU_IQEXT);
+		X6502_IRQEnd(FCEU_IQEXT2);
+		mapperFDS_transferflag = FALSE;
 		return ret;
 
 	case 0x4031:
 		ret = 0xFF;
-		if (isDiskInserted() && (mapperFDS_control & 0x04)) {
-			mapperFDS_diskaccess = 1;
-			if (mapperFDS_diskaddr < mapperFDS_blocklen) {
-				ret = disk_read(mapperFDS_blockstart + mapperFDS_diskaddr);
-				switch (mapperFDS_blockID) {
-				case DSK_FILEHDR:
-					switch (mapperFDS_diskaddr) {
-					case 13: mapperFDS_filesize = ret; break;
-					case 14: mapperFDS_filesize |= (ret << 8); break;
-					default: break;
-					}
-					break;
+		if (!isDiskInserted()) {
+			return ret;
+		}
+		if  (!(mapperFDS_control & 0x04)) {
+			return ret;
+		}
+		mapperFDS_diskaccess = 1;
+		if (mapperFDS_diskaddr < mapperFDS_blocklen) {
+			ret = disk_read(mapperFDS_blockstart + mapperFDS_diskaddr);
+			switch (mapperFDS_blockID) {
+			case DSK_FILEHDR:
+				switch (mapperFDS_diskaddr) {
+				case 13: mapperFDS_filesize = ret; break;
+				case 14: mapperFDS_filesize |= (ret << 8); break;
+				default: break;
 				}
-				mapperFDS_diskaddr++;
+				break;
 			}
-			DiskSeekIRQ = 150;
-			X6502_IRQEnd(FCEU_IQEXT2);
+			mapperFDS_diskaddr++;
 		}
+		DiskSeekIRQ = 150;
+		X6502_IRQEnd(FCEU_IQEXT2);
+		mapperFDS_transferflag = FALSE;
 		return ret;
 
 	case 0x4032:
-		ret = 0x40;
-		if (!isDiskInserted()) {
-			ret |= 5;
-		}
-		if (!isDiskInserted() || !(mapperFDS_control & 0x01) ||
-		    (mapperFDS_control & 0x02)) {
-			ret |= 2;
-		}
+		ret &= 0xF8;
+		/* disk not inserted, not writable */
+		ret |= !isDiskInserted() ? 0x05 : 0;
+		/* disk not inserted, not motorOn, resettransfer */
+		ret |= (!isDiskInserted() || !(mapperFDS_control & 0x01) || (mapperFDS_control & 0x02)) ? 0x02 : 0;
 		return ret;
 
 	case 0x4033:
 		return 0x80; /* battery */
-
-	case 0x4090:
-		return FDSEnvVolumeRead(A);
-
-	case 0x4092:
-		return FDSEnvModRead(A);
 	}
 
-	return cpu.openbus;
+	return ret;
 }
 
 static DECLFW(FDSWrite) {
-	if (!DiskIOEnabled && (A >= 0x4024)) {
-		return;
-	}
-
-	if ((A >= 0x4040) && (A <= 0x407F)) {
-		FDSWaveWrite(A, V);
-	}
-
 	switch (A) {
 	case 0x4020:
 		IRQLatch &= 0xFF00;
@@ -381,6 +375,9 @@ static DECLFW(FDSWrite) {
 				mapperFDS_diskaddr++;
 			}
 		}
+		DiskSeekIRQ = 150;
+		X6502_IRQEnd(FCEU_IQEXT2);
+		mapperFDS_transferflag = FALSE;
 		break;
 
 	case 0x4025:
@@ -424,46 +421,6 @@ static DECLFW(FDSWrite) {
 		mapperFDS_control = V;
 		setmirror(((V >> 3) & 1) ^ 1);
 		break;
-
-	case 0x4080:
-		FDSSReg0Write(A, V);
-		break;
-
-	case 0x4082:
-		FDSSReg1Write(A, V);
-		break;
-
-	case 0x4083:
-		FDSSReg2Write(A, V);
-		break;
-
-	case 0x4084:
-		FDSSReg3Write(A, V);
-		break;
-
-	case 0x4085:
-		FDSSReg4Write(A, V);
-		break;
-
-	case 0x4086:
-		FDSSReg5Write(A, V);
-		break;
-
-	case 0x4087:
-		FDSSReg6Write(A, V);
-		break;
-
-	case 0x4088:
-		FDSSReg7Write(A, V);
-		break;
-
-	case 0x4089:
-		FDSSReg8Write(A, V);
-		break;
-
-	case 0x408A:
-		FDSSReg9Write(A, V);
-		break;
 	}
 }