added protected template to replace std::array<>, chunked transfer for AVR

The AVR arduino platform doesn't have std::array. To use the chunked
transfer mode, I added a template to replace it. It has roughly the same
semantics as std::array<> and is protected to Adafruit_SPIDevice.

With this template, the chunked transfer is also possible for 8bit AVRs.

Author: eringerli

Adafruit_SPIDevice.cpp

@@ -7,13 +7,9 @@
 #if !defined(SPI_INTERFACES_COUNT) ||                                          \
     (defined(SPI_INTERFACES_COUNT) && (SPI_INTERFACES_COUNT > 0))
 
-//! constant for the buffer size for the chunked transfer
-constexpr size_t maxBufferSizeForChunkedTransfer = 64;
-
 //#define DEBUG_SERIAL Serial
 
 #ifdef DEBUG_SERIAL
-#if !defined(__AVR__)
 template <typename T>
 static void printChunk(const char *title, const T &buffer, const uint8_t size,
                        const uint16_t chunkNumber) {
@@ -32,7 +28,6 @@ static void printChunk(const char *title, const T &buffer, const uint8_t size,
   }
   DEBUG_SERIAL.println();
 }
-#endif
 
 static void printBuffer(const char *title, const uint8_t *buffer,
                         const size_t len) {
@@ -370,8 +365,7 @@ void Adafruit_SPIDevice::endTransactionWithDeassertingCS() {
 bool Adafruit_SPIDevice::write(const uint8_t *buffer, size_t len,
                                const uint8_t *prefix_buffer,
                                size_t prefix_len) {
-#if !defined(__AVR__)
-  std::array<uint8_t, maxBufferSizeForChunkedTransfer> chunkBuffer;
+  Array<uint8_t, maxBufferSizeForChunkedTransfer> chunkBuffer;
 
   auto chunkBufferIterator = chunkBuffer.begin();
 
@@ -421,26 +415,6 @@ bool Adafruit_SPIDevice::write(const uint8_t *buffer, size_t len,
 
   endTransactionWithDeassertingCS();
 
-#else // !defined(__AVR__)
-
-  beginTransactionWithAssertingCS();
-
-  for (size_t i = 0; i < prefix_len; i++) {
-    transfer(prefix_buffer[i]);
-  }
-  for (size_t i = 0; i < len; i++) {
-    transfer(buffer[i]);
-  }
-
-  endTransactionWithDeassertingCS();
-
-#ifdef DEBUG_SERIAL
-  printBuffer("write() prefix_buffer", prefix_buffer, prefix_len);
-  printBuffer("write() buffer", buffer, len);
-#endif
-
-#endif // !defined(__AVR__)
-
   return true;
 }
 
@@ -484,8 +458,7 @@ bool Adafruit_SPIDevice::read(uint8_t *buffer, size_t len, uint8_t sendvalue) {
 bool Adafruit_SPIDevice::write_then_read(const uint8_t *write_buffer,
                                          size_t write_len, uint8_t *read_buffer,
                                          size_t read_len, uint8_t sendvalue) {
-#if !defined(__AVR__)
-  std::array<uint8_t, maxBufferSizeForChunkedTransfer> chunkBuffer;
+  Array<uint8_t, maxBufferSizeForChunkedTransfer> chunkBuffer;
 
   auto chunkBufferIterator = chunkBuffer.begin();
 
@@ -570,27 +543,6 @@ bool Adafruit_SPIDevice::write_then_read(const uint8_t *write_buffer,
 
   endTransactionWithDeassertingCS();
 
-#else // !defined(__AVR__)
-
-  beginTransactionWithAssertingCS();
-
-  for (size_t i = 0; i < write_len; i++) {
-    transfer(write_buffer[i]);
-  }
-
-  for (size_t i = 0; i < read_len; i++) {
-    read_buffer[i] = transfer(sendvalue);
-  }
-
-  endTransactionWithDeassertingCS();
-
-#ifdef DEBUG_SERIAL
-  printBuffer("write_then_read() write_buffer", write_buffer, write_len);
-  printBuffer("write_then_read() read_buffer", read_buffer, read_len);
-#endif
-
-#endif // !defined(__AVR__)
-
   return true;
 }
 

Adafruit_SPIDevice.h

@@ -109,14 +109,71 @@ class Adafruit_SPIDevice {
   uint32_t _freq;
   BusIOBitOrder _dataOrder;
   uint8_t _dataMode;
+
   void setChipSelect(int value);
 
   int8_t _cs, _sck, _mosi, _miso;
 #ifdef BUSIO_USE_FAST_PINIO
   BusIO_PortReg *mosiPort, *clkPort, *misoPort, *csPort;
   BusIO_PortMask mosiPinMask, misoPinMask, clkPinMask, csPinMask;
 #endif
+
+  //! constant for the buffer size for the chunked transfer
+  static constexpr size_t maxBufferSizeForChunkedTransfer =
+#ifdef __AVR__
+      32;
+#else
+      64;
+#endif
   bool _begun;
+
+protected:
+  /*!
+   *    @brief  Template to encypsulate a C-array, provides STL-style accessors
+   * analoguous to std::array<>
+   *    @param  Type the type of the array
+   *    @param  Size the size of the array
+   */
+  template <typename Type, size_t Size> class Array {
+  public:
+    /*! @brief returns a pointer the start of the buffer
+     * @returns a pointer the start of the buffer
+     */
+    Type *begin() { return buffer; }
+
+    /*! @brief returns a pointer the one increment beyond the end of the buffer
+     * @returns a pointer the one increment beyond the end of the buffer
+     */
+    Type *end() { return endPointer; }
+
+    /*! @brief returns the size of the buffer
+     * @returns the size of the buffer
+     */
+    constexpr size_t size() { return Size; }
+
+    /*! @brief returns the buffer
+     * @returns the buffer
+     */
+    Type *data() { return buffer; }
+
+    /*! @brief returns a reference to the element at @param i
+     * @param i the index
+     * @returns a reference to the element at @param i
+     */
+    Type &operator[](size_t i) { return buffer[i]; }
+
+    /*! @brief returns a reference to the element at @param i
+     * @param i the index
+     * @returns a reference to the element at @param i
+     */
+    const Type &operator[](size_t i) const { return buffer[i]; }
+
+  private:
+    //! the buffer
+    Type buffer[Size];
+    //! address buffer one increment after the end
+    Type *endPointer = buffer + Size;
+  };
 };
 
 #endif // has SPI defined