Race in VCOM_lib fifo

VCOM_lib/serial_fifo.c

@@ -38,24 +38,27 @@ void fifo_init(fifo_t *fifo, U8 *buf)
 }
 
 
+// TBF: only non-isr may call this
 BOOL fifo_put(fifo_t *fifo, U8 c)
 {
-	int next;
+	int tail = fifo->tail;
+	int head = fifo->head;
 	
 	// check if FIFO has room
-	next = (fifo->head + 1) % VCOM_FIFO_SIZE;
+	int next = (head + 1) % VCOM_FIFO_SIZE;
-	if (next == fifo->tail) {
+	if (next == tail) {
 		// full
 		return FALSE;
 	}
 	
-	fifo->buf[fifo->head] = c;
+	fifo->buf[head] = c;
 	fifo->head = next;
 	
 	return TRUE;
 }
 
 
+// TBF: only USB isr may call this
 BOOL fifo_get(fifo_t *fifo, U8 *pc)
 {
 	int next;
@@ -74,12 +77,14 @@ BOOL fifo_get(fifo_t *fifo, U8 *pc)
 }
 
 
+// TBF: only USB isr may call this
 int fifo_avail(fifo_t *fifo)
 {
 	return (VCOM_FIFO_SIZE + fifo->head - fifo->tail) % VCOM_FIFO_SIZE;
 }
 
 
+// TBF: only USB isr may call this
 int fifo_free(fifo_t *fifo)
 {
 	return (VCOM_FIFO_SIZE - 1 - fifo_avail(fifo));

VCOM_lib/serial_fifo.h

@@ -26,13 +26,14 @@
 */
 
 #include "lpcusb_type.h"
+#include <atomic>
 
 #define VCOM_FIFO_SIZE	512
 
 typedef struct {
-	int		head;
+	std::atomic<int> head;
-	int 	tail;
+	std::atomic<int> tail;
-	U8		*buf;
+	U8  *buf;
 } fifo_t;
 
 void fifo_init(fifo_t *fifo, U8 *buf);

VCOM_lib/usbSerial.c

@@ -261,7 +261,7 @@ static void BulkIn(U8 bEP, U8 bEPStatus)
 		}
 	}
 	iLen = i;
-	
+
 	// send over USB
 	if (iLen > 0) {
 		USBHwEPWrite(bEP, abBulkBuf, iLen);
@@ -435,7 +435,7 @@ void VCOM_puts(const char* str)
 {
 	while(*str != '\0')
 	{
-		VCOM_putchar(*str++);
+		VCOM_putc(*str++);
 	}
 }
 void VCOM_putc(char c)