Adheres to the STM32F429 reference manual (RM0090) Section 10.3.17 DMA stream configuration procedure.

Before write access is permitted to numerous DMA registers, need to make sure that DMA is disabled for the stream. Disabling the stream is not instantaneous, and needs to be waited for (previous transmissions need to be finished first).

Added return values to numerous functions to signal a failure.

radio/src/opentx.cpp

@@ -1059,7 +1059,8 @@ void getADC()
 #endif
 
   DEBUG_TIMER_START(debugTimerAdcRead);
-  adcRead();
+  if (!adcRead())
+      TRACE("adcRead failed");
   DEBUG_TIMER_STOP(debugTimerAdcRead);
 
   for (uint8_t x=0; x<NUM_ANALOGS; x++) {