#174 FreeRTOS+IO Circular Buffer Overflow

[Corbin Weidner]

I found a bug in the circular buffer where an overflow causes the code to think the buffer is empty. This is due to a lack of a floating empty space in the buffer. I fixed this in my project by allocating one extra space and not including it in the length when writing to the buffer.

--- system/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-IO/Common/IOUtils_CircularBufferRx.c
+++ system/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-IO/Common/IOUtils_CircularBufferRx.c
@@ -77,11 +77,11 @@ Circular_Buffer_Rx_State_t *pxCircularBufferState;
                /* The semaphore was created correctly.  Fill in the private
                data structure. */


-               pxCircularBufferState->pucBufferStart = pvPortMalloc( xBufferSize );
+               pxCircularBufferState->pucBufferStart = pvPortMalloc( xBufferSize + 1 );

                if( pxCircularBufferState->pucBufferStart != NULL )
                {

-                   pxCircularBufferState->usBufferLength = ( uint16_t ) xBufferSize;
+                   pxCircularBufferState->usBufferLength = ( uint16_t ) xBufferSize + 1;
                    pxCircularBufferState->usErrorState = 0U;
                    pxCircularBufferState->usNextReadIndex = 0U;
                    pxCircularBufferState->usCharCount = 0U;

--- system/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-IO/Include/IOUtils_CircularBufferRx.h
+++ system/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-IO/Include/IOUtils_CircularBufferRx.h
@@ -67,7 +67,7 @@ 
uint16_t *pusNextWrite;                                                                                                 \
    while( ( xCondition ) )                                                                                             \
    {                                                                                                                   \
        /* If there is space in the circular buffer. */                                                                 \
-       if( pxCircularBufferRxState->usCharCount < pxCircularBufferRxState->usBufferLength )                            \
+       if( pxCircularBufferRxState->usCharCount < (pxCircularBufferRxState->usBufferLength - 1) )                      \
        {                                                                                                               \
            pxCircularBufferRxState->pucBufferStart[ *pusNextWrite ] = ( xReceiveFunction );                            \
            ulReceived++;                                                                                               \

[Kedar Patil]

IOUtils_CircularBufferRx.c
@@ -158,9 +158,7 @@ const portBASE_TYPE xMaxAttempts = 2;

                if( pxCircularBuffer->usNextReadIndex <= pxCircularBuffer->usNextWriteIndex )
                {

-                       /* How many bytes are available between the read and write
-                       indexes? */
-                       xBytesAvailable = ( pxCircularBuffer->usNextWriteIndex - pxCircularBuffer->usNextReadIndex );
+                       xBytesAvailable = pxCircularBuffer->usCharCount;
                }
                else
                {

The following change seems to work for me.