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.c

@@ -0,0 +1,122 @@
+/*
+ * Author:
+ * Copyright (c) 2015 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 <string.h>
+#include <stdlib.h>
+
+#include "vdiv.h"
+
+vdiv_context vdiv_init(int16_t pin, float voltage_ref)
+{
+    vdiv_context dev = (vdiv_context)malloc(sizeof(struct _vdiv_context));
+
+    if (dev == NULL) return NULL;
+
+    /* Init aio pin */
+    dev->aio = mraa_aio_init(pin);
+
+    if (dev->aio == NULL) {
+        free(dev);
+        return NULL;
+    }
+
+    /* Set defaults */
+    dev->m_aRef = 5.0;
+    dev->m_scale = 1.0;
+    dev->m_offset = 0.0;
+    dev->m_vdiv_sw = 3;
+
+    return dev;
+}
+
+void vdiv_close(vdiv_context dev)
+{
+    mraa_aio_close(dev->aio);
+    free(dev);
+}
+
+upm_result_t vdiv_set_scale(const vdiv_context dev, float scale)
+{
+    dev->m_scale = scale;
+    return UPM_SUCCESS;
+}
+
+upm_result_t vdiv_set_offset(const vdiv_context dev, float offset)
+{
+    dev->m_offset = offset;
+    return UPM_SUCCESS;
+}
+
+float vdiv_get_scale(const vdiv_context dev)
+{
+    return dev->m_scale;
+}
+
+float vdiv_get_offset(const vdiv_context dev)
+{
+    return dev->m_offset;
+}
+
+upm_result_t vdiv_set_divsw(const vdiv_context dev, int vdiv_sw)
+{
+    dev->m_vdiv_sw = vdiv_sw;
+    return UPM_SUCCESS;
+}
+
+int vdiv_get_divsw(const vdiv_context dev)
+{
+    return dev->m_vdiv_sw;
+}
+
+upm_result_t vdiv_get_raw_volts(const vdiv_context dev, float *value)
+{
+    *value = mraa_aio_read_float(dev->aio);
+    if (*value < 0)
+        return UPM_ERROR_OPERATION_FAILED;
+
+    /* Scale by the ADC reference voltage */
+    *value *= dev->m_aRef;
+
+    return UPM_SUCCESS;
+}
+
+upm_result_t vdiv_get_computed_volts(const vdiv_context dev, float *value)
+{
+    // JET - this is wrong.
+
+    *value = mraa_aio_read_float(dev->aio);
+    if (*value < 0)
+        return UPM_ERROR_OPERATION_FAILED;
+
+     /* Apply raw scale */
+    *value *= dev->m_scale;
+
+    /* Scale to the ADC referecen then to vdiv gain */
+    *value *= dev->m_aRef * dev->m_vdiv_sw;
+
+    /* Apply the offset in volts */
+    *value += dev->m_offset;
+
+    return UPM_SUCCESS;
+}