Diff: ADXL345.h

Revision:

3:7b83694c7292

Parent:

1:45faba962a46

Child:

4:8046894b947e

--- a/ADXL345.h	Sun Sep 09 15:37:26 2012 +0000
+++ b/ADXL345.h	Thu Sep 13 11:43:11 2012 +0000
@@ -1,4 +1,5 @@
 /**
+ * @file ADXL345.h
  * @author Uwe Gartmann
  * @author Used ITG3200 library developed Peter Swanson as template
  * A special thanks to Ewout van Bekkum for all his patient help in developing this library!
@@ -37,12 +38,12 @@
 #ifndef ADXL345_H
 #define ADXL345_H
 
-/**
+/*
  * Includes
  */
 #include "mbed.h"
 
-/**
+/*
  * Defines
  */
 //Registers.
@@ -113,7 +114,9 @@
 
 
 
-
+/**
+ * ADXL345 triple axis accelerometer.
+ */
 class ADXL345 {
 
 public:
@@ -554,6 +557,25 @@
      */
     int multiByteWrite(char startAddress, char* ptr_data, int size);
 
+private:
+
+    /**
+     * Converts little-endian 2's complement byte pair to native byte order of
+     * the CPU and then sign extend it to the CPU's register size.
+     *
+     * Implemented here to make the compiler inline expand it.
+     */
+    static int wordExtend(const char rx[2]){
+        // Readings are expressed in 16bit 2's complement, so we must first
+        // concatenate two bytes to make a word and sign extend it to obtain
+        // correct negative values.
+        // ARMCC compiles char as unsigned, which means no sign extension is
+        // performed during bitwise operations to chars. But we should make sure
+        // that lower byte won't extend its sign past upper byte for other
+        // compilers if we want to keep it portable.
+        return int16_t(((unsigned char)rx[1] << 8) | (unsigned char)rx[0]);
+    }
+
 };
 
 #endif /* ADXL345_H */