added write_and_read()

This method adds a wrapper for transfer() with CS-pin and
transaction management

Adafruit_SPIDevice.cpp

@@ -440,4 +440,32 @@ bool Adafruit_SPIDevice::write_then_read(uint8_t *write_buffer,
   return true;
 }
 
+/*!
+ *    @brief  Write some data and read some data at the same time from SPI
+ * into the same buffer. This is basicaly a wrapper for transfer() with
+ * CS-pin and transaction management.
+ * This /does/ transmit-receive at the same time!
+ *    @param  buffer Pointer to buffer of data to write/read to/from
+ *    @param  len Number of bytes from buffer to write/read.
+ *    @return Always returns true because there's no way to test success of SPI
+ * writes
+ */
+bool Adafruit_SPIDevice::write_and_read(uint8_t *buffer, size_t len) {
+  if (_spi) {
+    _spi->beginTransaction(*_spiSetting);
+  }
+
+  digitalWrite(_cs, LOW);
+
+  transfer(buffer, len);
+
+  digitalWrite(_cs, HIGH);
+
+  if (_spi) {
+    _spi->endTransaction();
+  }
+
+  return true;
+}
+
 #endif // SPI exists

Adafruit_SPIDevice.h

@@ -82,6 +82,7 @@ public:
   bool write_then_read(uint8_t *write_buffer, size_t write_len,
                        uint8_t *read_buffer, size_t read_len,
                        uint8_t sendvalue = 0xFF);
+  bool write_and_read(uint8_t *buffer, size_t len);
 
   uint8_t transfer(uint8_t send);
   void transfer(uint8_t *buffer, size_t len);