diff --git a/src/network/net_pcap.c b/src/network/net_pcap.c
index fe41e6281..18878db79 100644
--- a/src/network/net_pcap.c
+++ b/src/network/net_pcap.c
@@ -78,7 +78,7 @@ poll_thread(void *arg)
 
     /* As long as the channel is open.. */
     while (pcap != NULL) {
-	startnet();
+	network_mutex_wait(1);
 
 	network_wait_for_poll();
 
@@ -106,14 +106,12 @@ poll_thread(void *arg)
 	if (data == NULL)
 		thread_wait_event(evt, 10);
 
-	endnet();
+	network_mutex_wait(0);
     }
 
     thread_destroy_event(evt);
     poll_tid = NULL;
 
-    network_mutex_close();
-
     pclog("PCAP: polling stopped.\n");
 }
 
@@ -273,8 +271,6 @@ network_pcap_close(void)
 		;
 #endif
 
-	network_mutex_close();
-
 	/* OK, now shut down WinPcap itself. */
 	f_pcap_close(pc);
 	pc = pcap = NULL;
@@ -403,10 +399,10 @@ void
 network_pcap_in(uint8_t *bufp, int len)
 {
     if (pcap != NULL) {
-	network_busy_set();
+	network_busy(1);
 
 	f_pcap_sendpacket(pcap, bufp, len);
 
-	network_busy_clear();
+	network_busy(0);
     }
 }
diff --git a/src/network/net_slirp.c b/src/network/net_slirp.c
index 01987c47d..a664eba81 100644
--- a/src/network/net_slirp.c
+++ b/src/network/net_slirp.c
@@ -80,7 +80,7 @@ poll_thread(void *arg)
     evt = thread_create_event();
 
     while (slirpq != NULL) {
-	startnet();
+	network_mutex_wait(1);
 
 	network_wait_for_poll();
 
@@ -107,14 +107,12 @@ poll_thread(void *arg)
 	/* Done with this one. */
 	free(qp);
 
-	endnet();
+	network_mutex_wait(0);
     }
 
     thread_destroy_event(evt);
     evt = poll_tid = NULL;
 
-    network_mutex_close();
-
     pclog("SLiRP: polling stopped.\n");
 }
 
@@ -168,8 +166,6 @@ network_slirp_close(void)
 		;
 #endif
 
-        network_mutex_close();
-
 	/* OK, now shut down SLiRP itself. */
 	QueueDestroy(sl);
 	slirp_exit(0);
@@ -201,11 +197,11 @@ void
 network_slirp_in(uint8_t *pkt, int pkt_len)
 {
     if (slirpq != NULL) {
-	network_busy_set();
+	network_busy(1);
 
 	slirp_input((const uint8_t *)pkt, pkt_len);
 
-	network_busy_clear();
+	network_busy(0);
     }
 }
 
diff --git a/src/network/network.c b/src/network/network.c
index da68ec403..f74f20d16 100644
--- a/src/network/network.c
+++ b/src/network/network.c
@@ -54,31 +54,30 @@ int		network_card;
 netdev_t	network_devs[32];
 char		network_pcap[512];
 int		nic_do_log;
-static mutex_t	*netMutex;
+static volatile
+mutex_t	*netMutex;
 
 
 static struct
 {
-        int busy;
-	int queue_in_use;
+    volatile int
+    busy,
+    queue_in_use;
 
-        event_t *wake_poll_thread;
-        event_t *poll_complete;
-        event_t *queue_not_in_use;
+    volatile event_t
+    *wake_poll_thread,
+    *poll_complete,
+    *queue_not_in_use;
 } poll_data;
 
 
 void
-startnet(void)
+network_mutex_wait(uint8_t wait)
 {
-    thread_wait_mutex(netMutex);
-}
-
-
-void
-endnet(void)
-{
-    thread_release_mutex(netMutex);
+    if (wait)
+	thread_wait_mutex((mutex_t *) netMutex);
+    else
+	thread_release_mutex((mutex_t *) netMutex);
 }
 
 
@@ -86,46 +85,24 @@ void
 network_wait_for_poll()
 {
     while (poll_data.busy)
-	thread_wait_event(poll_data.poll_complete, -1);
-    thread_reset_event(poll_data.poll_complete);
+	thread_wait_event((event_t *) poll_data.poll_complete, -1);
+    thread_reset_event((event_t *) poll_data.poll_complete);
 }
 
 
 void
-network_mutex_init()
+network_thread_init(void)
 {
-    netMutex = thread_create_mutex(L"86Box.NetMutex");
-}
-
-
-void
-network_mutex_close()
-{
-    thread_close_mutex(netMutex);
-}
-
-
-void
-network_thread_init()
-{
-    network_mutex_init();
-
     poll_data.wake_poll_thread = thread_create_event();
     poll_data.poll_complete = thread_create_event();
 }
 
 void
-network_busy_set()
+network_busy(uint8_t set)
 {
-    poll_data.busy = 1;
-}
-
-
-void
-network_busy_clear()
-{
-    poll_data.busy = 0;
-    thread_set_event(poll_data.poll_complete);
+    poll_data.busy = !!set;
+    if (!set)
+	thread_set_event((event_t *) poll_data.poll_complete);
 }
 
 
@@ -184,6 +161,8 @@ network_attach(void *dev, uint8_t *mac, NETRXCB rx)
     net_cards[network_card].priv = dev;
     net_cards[network_card].rx = rx;
 
+    netMutex = thread_create_mutex(L"86Box.NetMutex");
+
     /* Start the platform module. */
     switch(network_type) {
 	case NET_TYPE_PCAP:
@@ -216,6 +195,8 @@ network_close(void)
 		network_slirp_close();
 		break;
     }
+
+    thread_close_mutex((event_t *) netMutex);
 }
 
 
diff --git a/src/network/network.h b/src/network/network.h
index d6602f6b2..db95e72cd 100644
--- a/src/network/network.h
+++ b/src/network/network.h
@@ -56,14 +56,12 @@ extern char	network_pcap[512];
 
 
 /* Function prototypes. */
-extern void	startnet(void);
-extern void	endnet(void);
-extern void	network_wait_for_poll();
-extern void	network_mutex_init();
-extern void	network_mutex_close();
-extern void	network_thread_init();
-extern void	network_busy_set();
-extern void	network_busy_clear();
+extern void	network_mutex_wait(uint8_t wait);
+extern void	network_wait_for_poll(void);
+extern void	network_mutex_init(void);
+extern void	network_mutex_close(void);
+extern void	network_thread_init(void);
+extern void	network_busy(uint8_t set);
 
 extern void	network_init(void);
 extern int	network_attach(void *, uint8_t *, NETRXCB);
diff --git a/src/scsi/scsi.c b/src/scsi/scsi.c
index cfa2d4942..3831d04dc 100644
--- a/src/scsi/scsi.c
+++ b/src/scsi/scsi.c
@@ -49,6 +49,7 @@ int		scsi_card_current = 0;
 int		scsi_card_last = 0;
 
 uint32_t	SCSI_BufferLength;
+static volatile
 mutex_t		*scsiMutex;
 
 
@@ -127,15 +128,12 @@ int scsi_card_get_from_internal_name(char *s)
 }
 
 
-void scsi_mutex_init(void)
+void scsi_mutex(uint8_t start)
 {
-    scsiMutex = thread_create_mutex(L"86Box.SCSIMutex");
-}
-
-
-void scsi_mutex_close(void)
-{
-    thread_close_mutex(scsiMutex);
+    if (start)
+	scsiMutex = thread_create_mutex(L"86Box.SCSIMutex");
+    else
+	thread_close_mutex((mutex_t *) scsiMutex);
 }
 
 
@@ -209,14 +207,10 @@ void SCSIReset(uint8_t id, uint8_t lun)
 
 
 void
-startscsi(void)
+scsi_mutex_wait(uint8_t wait)
 {
-    thread_wait_mutex(scsiMutex);
-}
-
-
-void
-endscsi(void)
-{
-    thread_release_mutex(scsiMutex);
+    if (wait)
+	thread_wait_mutex((mutex_t *) scsiMutex);
+    else
+	thread_release_mutex((mutex_t *) scsiMutex);
 }
diff --git a/src/scsi/scsi.h b/src/scsi/scsi.h
index 1f6bb1cde..092dd5650 100644
--- a/src/scsi/scsi.h
+++ b/src/scsi/scsi.h
@@ -294,8 +294,7 @@ extern device_t *scsi_card_getdevice(int card);
 extern int scsi_card_has_config(int card);
 extern char *scsi_card_get_internal_name(int card);
 extern int scsi_card_get_from_internal_name(char *s);
-extern void scsi_mutex_init(void);
-extern void scsi_mutex_close(void);
+extern void scsi_mutex(uint8_t start);
 extern void scsi_card_init(void);
 extern void scsi_card_reset(void);
 
@@ -354,5 +353,4 @@ typedef struct {
 
 #endif	/*EMU_SCSI_H*/
 
-extern void	startscsi(void);
-extern void	endscsi(void);
+extern void	scsi_mutex_wait(uint8_t wait);
diff --git a/src/scsi/scsi_aha154x.c b/src/scsi/scsi_aha154x.c
index d9e5cad3d..970dff1bb 100644
--- a/src/scsi/scsi_aha154x.c
+++ b/src/scsi/scsi_aha154x.c
@@ -265,11 +265,11 @@ aha_fast_cmds(void *p, uint8_t cmd)
     x54x_t *dev = (x54x_t *)p;
 
     if (cmd == CMD_BIOS_SCSI) {
-	x54x_busy_set();
+	x54x_busy(1);
 	dev->BIOSMailboxReq++;
 
 	x54x_thread_start(dev);
-	x54x_busy_clear();
+	x54x_busy(0);
 	return 1;
     }
 
@@ -361,7 +361,7 @@ aha_cmds(void *p)
 
 		case CMD_BIOS_MBINIT: /* BIOS Mailbox Initialization */
 			/* Sent by CF BIOS. */
-			x54x_busy_set();
+			x54x_busy(1);
 			dev->Mbx24bit = 1;
 
 			mbi = (MailboxInit_t *)dev->CmdBuf;
@@ -377,7 +377,7 @@ aha_cmds(void *p)
 
 			dev->Status &= ~STAT_INIT;
 			dev->DataReplyLeft = 0;
-			x54x_busy_clear();
+			x54x_busy(0);
 			break;
 
 		case CMD_MEMORY_MAP_1:	/* AHA memory mapper */
diff --git a/src/scsi/scsi_buslogic.c b/src/scsi/scsi_buslogic.c
index 95b945ee1..8c7b22eb5 100644
--- a/src/scsi/scsi_buslogic.c
+++ b/src/scsi/scsi_buslogic.c
@@ -692,7 +692,7 @@ buslogic_cmds(void *p)
 			dev->IrqEnabled = 1;
 		return 1;
 	case 0x81:
-		x54x_busy_set();
+		x54x_busy(1);
 		dev->Mbx24bit = 0;
 
 		MailboxInitE = (MailboxInitExtended_t *)dev->CmdBuf;
@@ -709,7 +709,7 @@ buslogic_cmds(void *p)
 
 		dev->Status &= ~STAT_INIT;
 		dev->DataReplyLeft = 0;
-		x54x_busy_clear();
+		x54x_busy(0);
 		break;
 	case 0x83:
 		if (dev->CmdParam == 12) {
diff --git a/src/scsi/scsi_x54x.c b/src/scsi/scsi_x54x.c
index 203fb3c44..adc646974 100644
--- a/src/scsi/scsi_x54x.c
+++ b/src/scsi/scsi_x54x.c
@@ -50,12 +50,16 @@
 
 static void	x54x_cmd_thread(void *priv);
 
-static thread_t	*poll_tid;
-static int	busy;
+static volatile
+thread_t	*poll_tid;
+static volatile
+int	busy;
 
-static event_t	*evt;
+static volatile
+event_t	*evt;
 
-static event_t	*poll_complete;
+static volatile
+event_t	*poll_complete;
 
 
 #ifdef ENABLE_X54X_LOG
@@ -1053,7 +1057,7 @@ x54x_scsi_cmd(x54x_t *dev)
     x54x_log("SCSIStatus = %02X\n", SCSIStatus);
 
     if (temp_cdb[0] == 0x42) {
-	thread_wait_event(evt, 10);
+	thread_wait_event((event_t *) evt, 10);
     }
 }
 
@@ -1287,10 +1291,10 @@ x54x_cmd_done(x54x_t *dev, int suppress);
 void
 x54x_wait_for_poll(void)
 {
-    if (x54x_busy()) {
-	thread_wait_event(poll_complete, -1);
+    if (x54x_is_busy()) {
+	thread_wait_event((event_t *) poll_complete, -1);
     }
-    thread_reset_event(poll_complete);
+    thread_reset_event((event_t *) poll_complete);
 }
 
 
@@ -1305,11 +1309,11 @@ x54x_cmd_thread(void *priv)
     {
 	if ((dev->Status & STAT_INIT) || (!dev->MailboxInit && !dev->BIOSMailboxInit) || (!dev->MailboxReq && !dev->BIOSMailboxReq)) {
 		/* If we did not get anything, wait a while. */
-		thread_wait_event(evt, 10);
+		thread_wait_event((event_t *) evt, 10);
 		continue;
 	}
 
-	startscsi();
+	scsi_mutex_wait(1);
 
 	if (!(dev->Status & STAT_INIT) && dev->MailboxInit && dev->MailboxReq)
 	{
@@ -1322,34 +1326,36 @@ x54x_cmd_thread(void *priv)
 		dev->ven_thread(dev);
 	}
 
-	endscsi();
+	scsi_mutex_wait(0);
     }
 
     if (poll_tid) {
-	thread_kill(poll_tid);
+	thread_kill((thread_t *) poll_tid);
 	poll_tid = NULL;
     }
 
     if (poll_complete) {
-	thread_destroy_event(poll_complete);
+	thread_destroy_event((event_t *) poll_complete);
 	poll_complete = NULL;
     }
 
     if (evt) {
-	thread_destroy_event(evt);
+	thread_destroy_event((event_t *) evt);
 	evt = NULL;
     }
 
-    scsi_mutex_close();
+    scsi_mutex(0);
 
     x54x_log("%s: Callback: polling stopped.\n", dev->name);
 }
 
 
 void
-x54x_busy_set(void)
+x54x_busy(uint8_t set)
 {
-    busy = 1;
+    busy = !!set;
+    if (!set)
+	    thread_set_event((event_t *) poll_complete);
 }
 
 
@@ -1363,16 +1369,8 @@ x54x_thread_start(x54x_t *dev)
 }
 
 
-void
-x54x_busy_clear(void)
-{
-    busy = 0;
-    x54x_log("Thread set event - poll complete\n");
-    thread_set_event(poll_complete);
-}
-
 uint8_t
-x54x_busy(void)
+x54x_is_busy(void)
 {
     return !!busy;
 }
@@ -1525,32 +1523,32 @@ x54x_out(uint16_t port, uint8_t val, void *priv)
     switch (port & 3) {
 	case 0:
 		if ((val & CTRL_HRST) || (val & CTRL_SRST)) {
-			x54x_busy_set();
+			x54x_busy(1);
 			reset = (val & CTRL_HRST);
 			x54x_log("Reset completed = %x\n", reset);
 			x54x_reset_ctrl(dev, reset);
 			x54x_log("Controller reset: ");
-			x54x_busy_clear();
+			x54x_busy(0);
 			break;
 		}
 		
 		if (val & CTRL_IRST) {
-			x54x_busy_set();
+			x54x_busy(1);
 			clear_irq(dev);
 			x54x_log("Interrupt reset: ");
-			x54x_busy_clear();
+			x54x_busy(0);
 		}
 		break;
 
 	case 1:
 		/* Fast path for the mailbox execution command. */
 		if ((val == CMD_START_SCSI) && (dev->Command == 0xff)) {
-			x54x_busy_set();
+			x54x_busy(1);
 			dev->MailboxReq++;
 
 			x54x_thread_start(dev);
 			x54x_log("Start SCSI command: ");
-			x54x_busy_clear();
+			x54x_busy(0);
 			return;
 		}
 		if (dev->ven_fast_cmds) {
@@ -1617,7 +1615,7 @@ x54x_out(uint16_t port, uint8_t val, void *priv)
 					break;
 
 				case CMD_MBINIT: /* mailbox initialization */
-					x54x_busy_set();
+					x54x_busy(1);
 					dev->Mbx24bit = 1;
 							
 					mbi = (MailboxInit_t *)dev->CmdBuf;
@@ -1636,7 +1634,7 @@ x54x_out(uint16_t port, uint8_t val, void *priv)
 					dev->Status &= ~STAT_INIT;
 					dev->DataReplyLeft = 0;
 					x54x_log("Mailbox init: ");
-					x54x_busy_clear();
+					x54x_busy(0);
 					break;
 
 				case CMD_BIOSCMD: /* execute BIOS */
@@ -1972,7 +1970,7 @@ x54x_init(device_t *info)
 
     timer_add(x54x_reset_poll, &dev->ResetCB, &dev->ResetCB, dev);
 
-    scsi_mutex_init();
+    scsi_mutex(1);
 
     poll_complete = thread_create_event();
 
@@ -1998,21 +1996,21 @@ x54x_close(void *priv)
 		free(dev->ven_data);
 
 	if (poll_tid) {
-		thread_kill(poll_tid);
+		thread_kill((thread_t *) poll_tid);
 		poll_tid = NULL;
 	}
 
 	if (poll_complete) {
-		thread_destroy_event(poll_complete);
+		thread_destroy_event((event_t *) poll_complete);
 		poll_complete = NULL;
 	}
 
 	if (evt) {
-		thread_destroy_event(evt);
+		thread_destroy_event((event_t *) evt);
 		evt = NULL;
 	}
 
-	scsi_mutex_close();
+	scsi_mutex(0);
 
 	if (dev->nvr != NULL)
 		free(dev->nvr);
diff --git a/src/scsi/scsi_x54x.h b/src/scsi/scsi_x54x.h
index f02c8e9e5..86b1ffde0 100644
--- a/src/scsi/scsi_x54x.h
+++ b/src/scsi/scsi_x54x.h
@@ -492,10 +492,9 @@ typedef struct
 
 
 extern void	x54x_reset_ctrl(x54x_t *dev, uint8_t Reset);
-extern void	x54x_busy_set(void);
+extern void	x54x_busy(uint8_t set);
 extern void	x54x_thread_start(x54x_t *dev);
-extern void	x54x_busy_clear(void);
-extern uint8_t	x54x_busy(void);
+extern uint8_t	x54x_is_busy(void);
 extern void	x54x_buf_alloc(uint8_t id, uint8_t lun, int length);
 extern void	x54x_buf_free(uint8_t id, uint8_t lun);
 extern uint8_t	x54x_mbo_process(x54x_t *dev);