Added sample averaging to MDx ADC driver

platform/drivers/ADC/ADC1_MDx.c

@@ -19,7 +19,19 @@
 #include "hwconfig.h"
 #include "ADC1_MDx.h"
 
-uint16_t measurements[4];
+/*
+ * Ringbuffer of samples to allow for value smoothing through averaging. This
+ * buffer is structured as follows:
+ *
+ * | vbat | rssi | vox | vol | vbat | rssi | vox | vol | ...
+ *
+ * thus it contains four samples of the four channels. Then, DMA is configured
+ * in circular mode with a rollover after 16 transfers, effectively managing
+ * this buffer as a ringbuffer for the measurements of the four channels.
+ * Then, in adc1_getMeasurement(), the average over the values contained in the
+ * ring buffer is performed and returned as the current channel value.
+ */
+uint16_t sampleRingBuf[16];
 
 void adc1_init()
 {
@@ -86,8 +98,8 @@ void adc1_init()
      * - no interrupts
      */
     DMA2_Stream0->PAR = ((uint32_t) &(ADC1->DR));
-    DMA2_Stream0->M0AR = ((uint32_t) &measurements);
-    DMA2_Stream0->NDTR = 4;
+    DMA2_Stream0->M0AR = ((uint32_t) &sampleRingBuf);
+    DMA2_Stream0->NDTR = 16;
     DMA2_Stream0->CR = DMA_SxCR_MSIZE_0
                      | DMA_SxCR_PSIZE_0
                      | DMA_SxCR_MINC
@@ -109,6 +121,15 @@ void adc1_terminate()
 float adc1_getMeasurement(uint8_t ch)
 {
     if(ch > 3) return 0.0f;
-    float value = ((float) measurements[ch]);
+
+    /* Return the average over the ring buffer */
+    float value = 0.0f;
+    for(uint8_t i = 0; i < 16; i += 4)
+    {
+        value += ((float) sampleRingBuf[i + ch]);
+    }
+    value /= 4.0f;
+
+    /* Return average value converted to mV */
     return (value * 3300.0f)/4096.0f;
 }