diff --git a/lib/README b/lib/README
index 90c38ede..e6bdb7fd 100644
--- a/lib/README
+++ b/lib/README
@@ -3,7 +3,9 @@ This directory contains external library code.
 The pjrc_usb_serial directory contains code from:
   http://www.pjrc.com/teensy/usb_serial.html
 version 1.7 (extracted on 20160605). It has been modified to compile
-on recent versions of gcc. See usb_serial.patch for the modifications.
+on recent versions of gcc, to support asynchronous notification of
+incoming data, and to not use SOF interrupts. See usb_serial.patch for
+the modifications.
 
 The cmsis-sam3x8e directory contains code from the Arduino project:
   https://www.arduino.cc/
diff --git a/lib/pjrc_usb_serial/usb_serial.c b/lib/pjrc_usb_serial/usb_serial.c
index ac5bc8a2..0c2488d5 100644
--- a/lib/pjrc_usb_serial/usb_serial.c
+++ b/lib/pjrc_usb_serial/usb_serial.c
@@ -325,7 +325,7 @@ void usb_init(void)
         UDCON = 0;				// enable attach resistor
 	usb_configuration = 0;
 	cdc_line_rtsdtr = 0;
-        UDIEN = (1<<EORSTE)|(1<<SOFE);
+        UDIEN = (1<<EORSTE);
 	sei();
 }
 
@@ -359,6 +359,7 @@ int16_t usb_serial_getchar(void)
 			UEINTX = 0x6B;
 			goto retry;
 		}	
+		UEIENX = (1<<RXOUTE);
 		SREG = intr_state;
 		return -1;
 	}
@@ -775,7 +776,14 @@ static inline void usb_ack_out(void)
 //
 ISR(USB_COM_vect)
 {
-        uint8_t intbits;
+        uint8_t intbits = UEINT;
+        if (intbits & (1<<CDC_RX_ENDPOINT)) {
+                UENUM = CDC_RX_ENDPOINT;
+                UEIENX = 0;
+                extern void sched_wake_tasks(void);
+                sched_wake_tasks();
+                return;
+        }
 	const uint8_t *list;
         const uint8_t *cfg;
 	uint8_t i, n, len, en;
diff --git a/lib/pjrc_usb_serial/usb_serial.patch b/lib/pjrc_usb_serial/usb_serial.patch
index 5aaa08e8..73fef81a 100644
--- a/lib/pjrc_usb_serial/usb_serial.patch
+++ b/lib/pjrc_usb_serial/usb_serial.patch
@@ -1,5 +1,5 @@
---- usb_serial.c	2011-04-19 05:54:12.000000000 -0400
-+++ usb_serial.c	2016-06-04 23:48:52.590001697 -0400
+--- ../../../lib/pjrc/usb_serial/usb_serial.c	2011-04-19 05:54:12.000000000 -0400
++++ usb_serial.c	2017-08-07 11:32:47.106357362 -0400
 @@ -30,6 +30,7 @@
  // Version 1.6: fix zero length packet bug
  // Version 1.7: fix usb_serial_set_control
@@ -62,7 +62,24 @@
  	uint16_t	wValue;
  	uint16_t	wIndex;
  	const uint8_t	*addr;
-@@ -646,7 +647,9 @@
+@@ -324,7 +325,7 @@
+         UDCON = 0;				// enable attach resistor
+ 	usb_configuration = 0;
+ 	cdc_line_rtsdtr = 0;
+-        UDIEN = (1<<EORSTE)|(1<<SOFE);
++        UDIEN = (1<<EORSTE);
+ 	sei();
+ }
+ 
+@@ -358,6 +359,7 @@
+ 			UEINTX = 0x6B;
+ 			goto retry;
+ 		}	
++		UEIENX = (1<<RXOUTE);
+ 		SREG = intr_state;
+ 		return -1;
+ 	}
+@@ -646,7 +648,9 @@
  // communication
  uint32_t usb_serial_get_baud(void)
  {
@@ -73,3 +90,19 @@
  }
  uint8_t usb_serial_get_stopbits(void)
  {
+@@ -772,7 +776,14 @@
+ //
+ ISR(USB_COM_vect)
+ {
+-        uint8_t intbits;
++        uint8_t intbits = UEINT;
++        if (intbits & (1<<CDC_RX_ENDPOINT)) {
++                UENUM = CDC_RX_ENDPOINT;
++                UEIENX = 0;
++                extern void sched_wake_tasks(void);
++                sched_wake_tasks();
++                return;
++        }
+ 	const uint8_t *list;
+         const uint8_t *cfg;
+ 	uint8_t i, n, len, en;
diff --git a/src/avr/serial.c b/src/avr/serial.c
index 10b95992..8b9dd14a 100644
--- a/src/avr/serial.c
+++ b/src/avr/serial.c
@@ -65,6 +65,8 @@ DECL_INIT(serial_init);
 ISR(USART0_RX_vect)
 {
     uint8_t data = UDR0;
+    if (data == MESSAGE_SYNC)
+        sched_wake_tasks();
     if (receive_pos >= sizeof(receive_buf))
         // Serial overflow - ignore it as crc error will force retransmit
         return;
@@ -104,6 +106,7 @@ console_pop_input(uint8_t len)
             memmove(&receive_buf[copied], &receive_buf[copied + len]
                     , needcopy - copied);
             copied = needcopy;
+            sched_wake_tasks();
         }
         irqstatus_t flag = irq_save();
         if (rpos != readb(&receive_pos)) {
diff --git a/src/avr/usbserial.c b/src/avr/usbserial.c
index 1b42d6d3..cc7bb12c 100644
--- a/src/avr/usbserial.c
+++ b/src/avr/usbserial.c
@@ -42,8 +42,10 @@ static void
 console_pop_input(uint8_t len)
 {
     uint8_t needcopy = receive_pos - len;
-    if (needcopy)
+    if (needcopy) {
         memmove(receive_buf, &receive_buf[len], needcopy);
+        sched_wake_tasks();
+    }
     receive_pos = needcopy;
 }
 
diff --git a/src/command.c b/src/command.c
index 53263a8f..87284ee8 100644
--- a/src/command.c
+++ b/src/command.c
@@ -11,7 +11,7 @@
 #include "board/misc.h" // crc16_ccitt
 #include "board/pgm.h" // READP
 #include "command.h" // output_P
-#include "sched.h" // DECL_TASK
+#include "sched.h" // sched_is_shutdown
 
 static uint8_t next_sequence = MESSAGE_DEST;
 
diff --git a/src/pru/main.c b/src/pru/main.c
index 3c2a2725..04d440df 100644
--- a/src/pru/main.c
+++ b/src/pru/main.c
@@ -85,7 +85,10 @@ timer_kick(void)
 static void
 _irq_poll(void)
 {
-    if (CT_INTC.SECR0 & (1 << IEP_EVENT)) {
+    uint32_t secr0 = CT_INTC.SECR0;
+    if (secr0 & (1 << KICK_PRU1_EVENT))
+        sched_wake_tasks();
+    if (secr0 & (1 << IEP_EVENT)) {
         CT_IEP.TMR_CMP_STS = 0xff;
         uint32_t next = timer_dispatch_many();
         timer_set(next);
@@ -121,7 +124,6 @@ console_task(void)
     const struct command_parser *cp = SHARED_MEM->next_command;
     if (!cp)
         return;
-    barrier();
 
     if (sched_is_shutdown() && !(cp->flags & HF_IN_SHUTDOWN)) {
         sched_report_shutdown();
diff --git a/src/sam3x8e/serial.c b/src/sam3x8e/serial.c
index 713c6337..7741d6f8 100644
--- a/src/sam3x8e/serial.c
+++ b/src/sam3x8e/serial.c
@@ -56,6 +56,8 @@ UART_Handler(void)
     uint32_t status = UART->UART_SR;
     if (status & UART_SR_RXRDY) {
         uint8_t data = UART->UART_RHR;
+        if (data == MESSAGE_SYNC)
+            sched_wake_tasks();
         if (receive_pos >= sizeof(receive_buf))
             // Serial overflow - ignore it as crc error will force retransmit
             return;
@@ -94,6 +96,7 @@ console_pop_input(uint32_t len)
             memmove(&receive_buf[copied], &receive_buf[copied + len]
                     , needcopy - copied);
             copied = needcopy;
+            sched_wake_tasks();
         }
         irqstatus_t flag = irq_save();
         if (rpos != readl(&receive_pos)) {
diff --git a/src/sched.c b/src/sched.c
index 0aadcc75..a2f5fea8 100644
--- a/src/sched.c
+++ b/src/sched.c
@@ -28,6 +28,9 @@ static struct timer sentinel_timer, deleted_timer;
 static uint_fast8_t
 periodic_event(struct timer *t)
 {
+    // Make sure the stats task runs periodically
+    sched_wake_tasks();
+    // Reschedule timer
     periodic_timer.waketime += timer_from_us(100000);
     sentinel_timer.waketime = periodic_timer.waketime + 0x80000000;
     return SF_RESCHEDULE;
@@ -177,10 +180,17 @@ sched_timer_reset(void)
  * Task waking
  ****************************************************************/
 
+// Note that at least one task is ready to run
+void
+sched_wake_tasks(void)
+{
+}
+
 // Note that a task is ready to run
 void
 sched_wake_task(struct task_wake *w)
 {
+    sched_wake_tasks();
     writeb(&w->wake, 1);
 }
 
diff --git a/src/sched.h b/src/sched.h
index bb6bb975..ba883778 100644
--- a/src/sched.h
+++ b/src/sched.h
@@ -29,6 +29,7 @@ struct task_wake {
 void sched_add_timer(struct timer*);
 void sched_del_timer(struct timer *del);
 unsigned int sched_timer_dispatch(void);
+void sched_wake_tasks(void);
 void sched_wake_task(struct task_wake *w);
 uint8_t sched_check_wake(struct task_wake *w);
 uint8_t sched_is_shutdown(void);