add logic to detect system byte order at runtime; used this logic on the I2C bus to determine if uint16_t transfers need to swap bytes; note- Arduino SPI does this correctly

Author: gigapod

src/sfeTk/sfeTkIBus.h

@@ -27,7 +27,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 #pragma once
 
-#include "sfeTkError.h"
+#include "sfeToolkit.h"
 #include <stddef.h>
 
 /**

src/sfeTk/sfeToolkit.h

@@ -30,3 +30,19 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
     @brief Common include file for the core of the SparkFun Electronics Toolkit
 */
 #include "sfeTkError.h"
+
+/**
+    @brief The byte order of the system
+*/
+typedef enum
+{
+    SFETK_BIG_ENDIAN = 0x01,
+    SFETK_LITTLE_ENDIAN = 0x00
+} sfeTKByteOrder_t;
+
+// Runtime check for system byte order
+constexpr sfeTKByteOrder_t systemByteOrder(void)
+{
+    uint16_t i = 1;
+    return *((uint8_t *)&i) == 0 ? SFETK_BIG_ENDIAN : SFETK_LITTLE_ENDIAN;
+}

src/sfeTkArdI2C.cpp

@@ -222,12 +222,16 @@ sfeTkError_t sfeTkArdI2C::writeRegister16Region(uint16_t devReg, const uint8_t *
 //
 sfeTkError_t sfeTkArdI2C::writeRegister16Region16(uint16_t devReg, const uint16_t *data, size_t length)
 {
-    devReg = ((devReg << 8) & 0xff00) | ((devReg >> 8) & 0x00ff);
+    // if the system byte order is the same as the desired order, just send the buffer
+    if (systemByteOrder() == _byteOrder)
+        return writeRegisterRegionAddress((uint8_t *)&devReg, 2, (uint8_t *)data, length * 2);
 
+    // okay, we need to swap
+    devReg = ((devReg << 8) & 0xff00) | ((devReg >> 8) & 0x00ff);
     uint16_t data16[length];
-    // TODO determine local endianess and convert if needed
     for (size_t i = 0; i < length; i++)
         data16[i] = ((data[i] << 8) & 0xff00) | ((data[i] >> 8) & 0x00ff);
+
     return writeRegisterRegionAddress((uint8_t *)&devReg, 2, (uint8_t *)data16, length * 2);
 }
 
@@ -384,11 +388,14 @@ sfeTkError_t sfeTkArdI2C::readRegister16Region(uint16_t devReg, uint8_t *data, s
 //
 sfeTkError_t sfeTkArdI2C::readRegister16Region16(uint16_t devReg, uint16_t *data, size_t numBytes, size_t &readBytes)
 {
-    devReg = ((devReg << 8) & 0xff00) | ((devReg >> 8) & 0x00ff);
+    // if the system byte order is the same as the desired order, flip the address
+    if (systemByteOrder() != _byteOrder)
+        devReg = ((devReg << 8) & 0xff00) | ((devReg >> 8) & 0x00ff);
+
     sfeTkError_t status = readRegisterRegionAnyAddress((uint8_t *)&devReg, 2, (uint8_t *)data, numBytes * 2, readBytes);
 
-    // TODO determine local endianess and convert if needed
-    if (status == kSTkErrOk)
+    // Do we need to flip the byte order?
+    if (status == kSTkErrOk && systemByteOrder() != _byteOrder)
     {
         for (size_t i = 0; i < numBytes; i++)
             data[i] = ((data[i] << 8) & 0xff00) | ((data[i] >> 8) & 0x00ff);

src/sfeTkArdI2C.h

@@ -41,9 +41,10 @@ class sfeTkArdI2C : public sfeTkII2C
 {
   public:
     /**
-        @brief Constructor
+    @brief Constructor
     */
-    sfeTkArdI2C(void) : _i2cPort(nullptr), _bufferChunkSize{kDefaultBufferChunk}
+
+    sfeTkArdI2C(void) : _i2cPort(nullptr), _bufferChunkSize{kDefaultBufferChunk}, _byteOrder{SFETK_LITTLE_ENDIAN}
     {
     }
     /**
@@ -291,6 +292,15 @@ class sfeTkArdI2C : public sfeTkII2C
         return _bufferChunkSize;
     }
 
+    /**
+     * @brief Set the byte order for multi-byte data transfers
+     *
+     */
+    void setByteOrder(sfeTKByteOrder_t order)
+    {
+        _byteOrder = order;
+    }
+
   protected:
     // note: The wire port is protected, allowing access if a sub-class is
     //      created to implement a special read/write routine
@@ -309,4 +319,7 @@ class sfeTkArdI2C : public sfeTkII2C
 
     /** The I2C buffer chunker - chunk size*/
     size_t _bufferChunkSize;
+
+    /** flag to manage byte swapping */
+    sfeTKByteOrder_t _byteOrder;
 };