vdiv: Added vdiv C source.

Multiple changes related to building the vdiv c source w/c example.

    * Renamed GroveVdiv to vdiv (all cases) throughout source, examples,
    directory names, and documentation.

    * Added C source.

    * Tested C sensor code on edison

    * Updated CMakeLists.txt for examples-c to build from
    <sensorname>-c.  This was a small change to get c examples to build
    for sensors in which the C++ does NOT wrap the C.

    * Added C example for vdiv.

Signed-off-by: Noel Eck <noel.eck@intel.com>

src/vdiv/vdiv.cxx

@@ -0,0 +1,68 @@
+/*
+ * Author: Jon Trulson <jtrulson@ics.com>
+ * Copyright (c) 2014 Intel Corporation.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <iostream>
+#include <string>
+#include <stdexcept>
+
+#include "vdiv.hpp"
+
+using namespace upm;
+using namespace std;
+
+VDiv::VDiv(int pin)
+{
+  if ( !(m_aio = mraa_aio_init(pin)) )
+    {
+      throw std::invalid_argument(std::string(__FUNCTION__) +
+                                  ": mraa_aio_init() failed, invalid pin?");
+      return;
+    }
+}
+
+VDiv::~VDiv()
+{
+  mraa_aio_close(m_aio);
+}
+
+unsigned int VDiv::value(unsigned int samples)
+{
+  unsigned int sum = 0;
+
+  for (int i=0; i<samples; i++)
+    {
+      sum += mraa_aio_read(m_aio);
+      if (sum == -1) return 0;
+      usleep(2000);
+    }
+        
+  return (sum / samples);
+}
+
+float VDiv::computedValue(uint8_t gain, unsigned int val, int vref, int res)
+{
+  return ((float(gain) * float(val) * float(vref) / float(res)) / 1000.0);
+
+}
+