Fix I2C slave issue: Rx buffer allocation

Fix #212

Signed-off-by: Frederic.Pillon <frederic.pillon@st.com>

Author: fpistm

libraries/Wire/src/Wire.cpp

@@ -380,6 +380,14 @@ void TwoWire::onReceiveService(uint8_t* inBytes, int numBytes)
   if(rxBufferIndex < rxBufferLength){
     return;
   }
+
+  if(rxBuffer == nullptr){
+    allocateRxBuffer(numBytes);
+    // error if no memory block available to allocate the buffer
+    if(rxBuffer == nullptr){
+      Error_Handler();
+    }
+  }
   // copy twi rx buffer into local read buffer
   // this enables new reads to happen in parallel
   memcpy(rxBuffer, inBytes, numBytes);
@@ -423,7 +431,7 @@ void TwoWire::onRequest( void (*function)(void) )
   * @note   Minimum allocated size is BUFFER_LENGTH)
   * @param  length: number of bytes to allocate
   */
-inline void TwoWire::allocateRxBuffer(size_t length)
+void TwoWire::allocateRxBuffer(size_t length)
 {
   if(rxBufferAllocated < length) {
   // By default we allocate BUFFER_LENGTH bytes. It is the min size of the buffer.

libraries/Wire/src/Wire.h

@@ -58,7 +58,7 @@ class TwoWire : public Stream
     static void onRequestService(void);
     static void onReceiveService(uint8_t*, int);
 
-    void allocateRxBuffer(size_t length);
+    static void allocateRxBuffer(size_t length);
     void allocateTxBuffer(size_t length);
 
     void resetRxBuffer(void);