diff --git a/Makefile b/Makefile
index 0a7dbd4..fdebc9e 100644
--- a/Makefile
+++ b/Makefile
@@ -29,12 +29,14 @@ INCLUDES =                                        \
     -I grbl                                       \
     -I lpc17xx                                    \
     -I smoother                                   \
+    -I VCOM_lib                                   \
 
 # Compile all .c and .cpp files in these directories
 # Hack: .c files are compiled as if they were c++.
 SRC_DIRS =          \
 	grbl            \
     smoother        \
+    VCOM_lib        \
 
 # Compile all .c files in these directories, except ones on the exclude list.
 # These files get extra -Wno-* flags to reduce spam.
diff --git a/VCOM_lib/lpcusb_type.h b/VCOM_lib/lpcusb_type.h
index 1c76543..494c332 100644
--- a/VCOM_lib/lpcusb_type.h
+++ b/VCOM_lib/lpcusb_type.h
@@ -40,9 +40,6 @@
 #ifndef _LPCUSB_TYPE_H_
 #define _LPCUSB_TYPE_H_
 
-// CodeRed - include NXP-produced type.h file
-#include "type.h"
-
 typedef unsigned char		U8;		/**< unsigned 8-bit */
 typedef unsigned short int	U16;	/**< unsigned 16-bit */
 typedef unsigned int		U32;	/**< unsigned 32-bit */
@@ -50,10 +47,10 @@ typedef unsigned int		U32;	/**< unsigned 32-bit */
 
 // CodeRed - comment out defines duplicated in NXP type.h
 
-//typedef int					BOOL;	/**< #TRUE or #FALSE */
+typedef int					BOOL;	/**< #TRUE or #FALSE */
 
-//#define	TRUE	1					/**< TRUE */
-//#define FALSE	0					/**< FALSE */
+#define	TRUE	1					/**< TRUE */
+#define FALSE	0					/**< FALSE */
 
 //#ifndef NULL
 //#define NULL	((void*)0)			/**< NULL pointer */
diff --git a/VCOM_lib/usbSerial.c b/VCOM_lib/usbSerial.c
index fc3e31b..ceed39e 100644
--- a/VCOM_lib/usbSerial.c
+++ b/VCOM_lib/usbSerial.c
@@ -60,6 +60,9 @@ void VCOM_gets_echo(char *str); // gets string terminated in '\r' or '\n' and ec
 
 */
 
+/* Modified by Todd Fleming (TBF), 2017
+   Replaced read polling API with callback API
+*/
 
 #include "usbSerial.h"
 
@@ -78,10 +81,12 @@ static U8 abBulkBuf[64];
 static U8 abClassReqData[8];
 
 static U8 txdata[VCOM_FIFO_SIZE];
-static U8 rxdata[VCOM_FIFO_SIZE];
+//static U8 rxdata[VCOM_FIFO_SIZE];
 
 static fifo_t txfifo;
-static fifo_t rxfifo;
+//static fifo_t rxfifo;
+
+static UsbSerialReadCallback* usbSerialReadCallback = nullptr;
 
 // forward declaration of interrupt handler
 void USBIntHandler(void);
@@ -207,15 +212,20 @@ static const U8 abDescriptors[] = {
  */
 static void BulkOut(U8 bEP, U8 bEPStatus)
 {
-	int i, iLen;
+	int iLen;
 	bEPStatus = bEPStatus;
+	/* TBF: replaced rxfifo with callback
 	if (fifo_free(&rxfifo) < MAX_PACKET_SIZE) {
 		// may not fit into fifo
 		return;
 	}
+	*/
 
 	// get data from USB into intermediate buffer
 	iLen = USBHwEPRead(bEP, abBulkBuf, sizeof(abBulkBuf));
+	if(usbSerialReadCallback)
+		usbSerialReadCallback(abBulkBuf, iLen);
+	/* TBF: replaced rxfifo with callback
 	for (i = 0; i < iLen; i++) {
 		// put into FIFO
 		if (!fifo_put(&rxfifo, abBulkBuf[i])) {
@@ -224,6 +234,7 @@ static void BulkOut(U8 bEP, U8 bEPStatus)
 			break;
 		}
 	}
+	*/
 }
 
 
@@ -307,7 +318,7 @@ static BOOL HandleClassRequest(TSetupPacket *pSetup, int *piLen, U8 **ppbData)
 void VCOM_init(void)
 {
 	fifo_init(&txfifo, txdata);
-	fifo_init(&rxfifo, rxdata);
+	//fifo_init(&rxfifo, rxdata);
 }
 
 
@@ -328,13 +339,14 @@ int VCOM_putchar(int c)
 	
 	@returns character read, or EOF if character could not be read
  */
+/* TBF: replaced with callback
 int VCOM_getchar(void)
 {
 	U8 c;
 	
 	return fifo_get(&rxfifo, &c) ? c : EOF;
 }
-
+*/
 
 /**
 	Interrupt handler
@@ -342,7 +354,7 @@ int VCOM_getchar(void)
 	Simply calls the USB ISR
  */
 //void USBIntHandler(void)
-void USB_IRQHandler(void)
+extern "C" void USB_IRQHandler(void)
 {
 	USBHwISR();
 }
@@ -364,8 +376,10 @@ void enable_USB_interrupts(void);
 	main
 	====
 **************************************************************************/
-int usbSerialInit()
+int usbSerialInit(UsbSerialReadCallback* usbSerialReadCallback)
 {
+	::usbSerialReadCallback = usbSerialReadCallback;
+
 	// initialise stack
 	USBInit();
 
@@ -428,6 +442,7 @@ void VCOM_putc(char c)
 {
 	while(VCOM_putchar(c) == EOF);
 }
+/* TBF: replaced with callback
 char VCOM_getc()
 {
 	int c;
@@ -438,6 +453,7 @@ char VCOM_getc()
 	}
 	return (char)c;
 }
+*/
 void VCOM_putHex(uint8_t hex)
 {
 	uint8_t temp;
@@ -454,6 +470,7 @@ void VCOM_putHex(uint8_t hex)
 		
 	VCOM_putc((char)temp);
 }
+/* TBF: replaced with callback
 void VCOM_gets(char* str)
 {
 	char c;
@@ -483,7 +500,7 @@ void VCOM_gets_echo(char *str)
 	}
 	*str = '\0';
 }
-
+*/
 /* Original code by ELM_ChaN. Modified by Martin Thomas */
 int xatoi (char **str, long *res)
 {
diff --git a/VCOM_lib/usbSerial.h b/VCOM_lib/usbSerial.h
index 568cd1b..e05db60 100644
--- a/VCOM_lib/usbSerial.h
+++ b/VCOM_lib/usbSerial.h
@@ -60,11 +60,15 @@ void VCOM_gets_echo(char *str); // gets string terminated in '\r' or '\n' and ec
 
 */
 
+/* Modified by Todd Fleming (TBF), 2017
+   Replaced read polling API with callback API
+*/
+
 #ifndef __USB_SERIAL_H__
 #define __USB_SERIAL_H__
 
 #ifdef __cplusplus
-extern "C" {
+//extern "C" {
 #endif
 
 #include <stdarg.h>
@@ -94,8 +98,10 @@ extern "C" {
 
 #include "serial_fifo.h"
 
-int usbSerialInit(); // run once in main b4 main loop starts.
+// Receives serial data. Called by an interrupt.
+typedef void UsbSerialReadCallback(const U8* data, unsigned len);
 
+int usbSerialInit(UsbSerialReadCallback* usbSerialReadCallback); // run once in main b4 main loop starts.
 
 /*
 	Writes one character to VCOM port
@@ -110,20 +116,20 @@ int VCOM_putchar(int c);
 	
 	@returns character read, or EOF if character could not be read
  */
-int VCOM_getchar(void);
+//int VCOM_getchar(void);
 
 void VCOM_puts(const char* str); //writes a null terminated string. 
 void VCOM_putc(char c); // writes a character.
 void VCOM_putHex(uint8_t hex); // writes 0x.. hex value on the terminal.
-char VCOM_getc(); // returns character entered in the terminal. blocking function
-void VCOM_gets(char* str); // returns a string. '\r' or '\n' will terminate character collection.
-char VCOM_getc_echo(); // returns character entered and echoes the same back.
-void VCOM_gets_echo(char *str); // gets string terminated in '\r' or '\n' and echoes back the same.
+//char VCOM_getc(); // returns character entered in the terminal. blocking function
+//void VCOM_gets(char* str); // returns a string. '\r' or '\n' will terminate character collection.
+//char VCOM_getc_echo(); // returns character entered and echoes the same back.
+//void VCOM_gets_echo(char *str); // gets string terminated in '\r' or '\n' and echoes back the same.
 
 void VCOM_printf(const char* str, ...); // Original code by Elm_CHaN. Modified by Martin Thomas
 
 #ifdef __cplusplus
-}
+//}
 #endif
 
 #endif
\ No newline at end of file
diff --git a/VCOM_lib/usbcontrol.c b/VCOM_lib/usbcontrol.c
index df96714..f4d671c 100644
--- a/VCOM_lib/usbcontrol.c
+++ b/VCOM_lib/usbcontrol.c
@@ -118,6 +118,7 @@ static void StallControlPipe(U8 bEPStat)
 // dump setup packet
 	DBG("STALL on [");
 	pb = (U8 *)&Setup;
+	pb = pb;
 	for (i = 0; i < 8; i++) {
 		DBG(" %02x", *pb++);
 	}
diff --git a/grbl/serial.c b/grbl/serial.c
index 0dc9228..420db7d 100644
--- a/grbl/serial.c
+++ b/grbl/serial.c
@@ -20,7 +20,14 @@
 */
 
 #include "grbl.h"
+
+#define USE_USB
+
+#ifdef USE_USB
+#include "usbSerial.h"
+#else
 #include "Driver_USART.h"
+#endif
 
 #define RX_RING_BUFFER (RX_BUFFER_SIZE+1)
 #define TX_RING_BUFFER (TX_BUFFER_SIZE+1)
@@ -33,8 +40,10 @@ uint8_t serial_tx_buffer[TX_RING_BUFFER];
 uint8_t serial_tx_buffer_head = 0;
 volatile uint8_t serial_tx_buffer_tail = 0;
 
+#ifndef USE_USB
 extern ARM_DRIVER_USART Driver_USART0;
 #define serialDriver Driver_USART0
+#endif
 
 void serialInterrupt(uint32_t event);
 void legacy_ISR(uint8_t data);
@@ -70,6 +79,12 @@ uint8_t serial_get_tx_buffer_count()
 
 void serial_init()
 {
+#ifdef USE_USB
+  usbSerialInit([](const U8* data, unsigned len) {
+    while(len--)
+      legacy_ISR(*data++);
+  });
+#else
   int32_t uartFlags = ARM_USART_MODE_ASYNCHRONOUS |
                       ARM_USART_DATA_BITS_8 |
                       ARM_USART_PARITY_NONE |
@@ -84,6 +99,7 @@ void serial_init()
 
   //Issue first read
   serialDriver.Receive(arm_rx_buf, 1);
+#endif
 }
 
 void legacy_serial_init()
@@ -107,6 +123,12 @@ void legacy_serial_init()
 
 // Writes one byte to the TX serial buffer. Called by main program.
 void serial_write(uint8_t data) {
+#ifdef USE_USB
+  while(VCOM_putchar(data) == EOF) {
+    // TODO: Restructure st_prep_buffer() calls to be executed here during a long print.
+    if (sys_rt_exec_state & EXEC_RESET) { return; } // Only check for abort to avoid an endless loop.
+  }
+#else
   //We're just really cheating here. We dont need the grbl fifo because the driver already
   //provides one. But we have to have a place to keep the data safe until the driver has completed
   //the transmit and is ready for more bytes.
@@ -120,6 +142,7 @@ void serial_write(uint8_t data) {
   // the original GRBL TX Interrupt.
   serial_tx_buffer[0] = data;
   serialDriver.Send(serial_tx_buffer, 1);
+#endif
 }
 
 // Writes one byte to the TX serial buffer. Called by main program.
@@ -145,6 +168,7 @@ void legacy_serial_write(uint8_t data) {
 //Device driver interrupt
 // The CMSIS Driver doesn't have seperate interrupts/callbacks available for TX and RX but instead
 // is a single composite interrupt.
+#ifndef USE_USB
 void serialInterrupt(uint32_t event) {
   if (event & ARM_USART_EVENT_RECEIVE_COMPLETE) {
     //We got our single byte read, so put the data into our fifo and issue another read
@@ -152,6 +176,7 @@ void serialInterrupt(uint32_t event) {
     serialDriver.Receive(arm_rx_buf, 1);
   }
 }
+#endif
 
 //We don't use TX interrupts directly with the ARM Driver.
 // Data Register Empty Interrupt handler