fix adc.begin() to correctly initialize channels according to selected pins

Author: leonardocavagnis

src/AdvancedADC.cpp

@@ -29,18 +29,19 @@ struct adc_descr_t {
     IRQn_Type dma_irqn;
     TIM_HandleTypeDef tim;
     uint32_t  tim_trig;
-    uint32_t  pin_alt;
     DMABufferPool<Sample> *pool;
     DMABuffer<Sample> *dmabuf[2];
 };
 
+static uint32_t pin_alt[3] = {0, ALT0, ALT1};
+
 static adc_descr_t adc_descr_all[3] = {
     {{ADC1}, {DMA1_Stream1, {DMA_REQUEST_ADC1}}, DMA1_Stream1_IRQn, {TIM1}, ADC_EXTERNALTRIG_T1_TRGO,
-        0, nullptr, {nullptr, nullptr}},
+        nullptr, {nullptr, nullptr}},
     {{ADC2}, {DMA1_Stream2, {DMA_REQUEST_ADC2}}, DMA1_Stream2_IRQn, {TIM2}, ADC_EXTERNALTRIG_T2_TRGO,
-        ALT0, nullptr, {nullptr, nullptr}},
+        nullptr, {nullptr, nullptr}},
     {{ADC3}, {DMA1_Stream3, {DMA_REQUEST_ADC3}}, DMA1_Stream3_IRQn, {TIM3}, ADC_EXTERNALTRIG_T3_TRGO,
-        ALT1, nullptr, {nullptr, nullptr}},
+        nullptr, {nullptr, nullptr}},
 };
 
 static uint32_t ADC_RES_LUT[] = {
@@ -121,13 +122,28 @@ int AdvancedADC::begin(uint32_t resolution, uint32_t sample_rate, size_t n_sampl
         return 0;
     }
 
+    // Clear ALTx pin.
+    for (size_t i=0; i<n_channels; i++) {
+        for (size_t j=0; j<AN_ARRAY_SIZE(pin_alt); j++) {
+            adc_pins[i] = (PinName) (adc_pins[i] & ~(uint32_t)pin_alt[j]);
+        }  
+    }
+    
     // Find an ADC that can be used with these set of pins/channels.
-    for (size_t i=0; instance == ADC_NP && i<AN_ARRAY_SIZE(adc_descr_all); i++) {
-        descr = &adc_descr_all[i];
-        if (descr->pool == nullptr) {
-            // Check if the first channel is connected to this ADC.
-            PinName pin = (PinName) (adc_pins[0] | descr->pin_alt);
-            instance = (ADCName) pinmap_peripheral(pin, PinMap_ADC);
+    for (size_t i=0; instance == ADC_NP && i<AN_ARRAY_SIZE(pin_alt); i++) {
+        // Calculate alternate function pin.
+        PinName pin = (PinName) (adc_pins[0] | pin_alt[i]); // First pin decides the ADC.
+
+        // Check if pin is mapped.
+        if (pinmap_find_peripheral(pin, PinMap_ADC) == NC) break;
+
+        // Find the first free ADC according to the available ADCs on pin.
+        for (size_t j=0; instance == ADC_NP && j<AN_ARRAY_SIZE(adc_descr_all); j++) {
+            descr = &adc_descr_all[j];
+            if (descr->pool == nullptr && ((ADC_TypeDef*)pinmap_peripheral(pin, PinMap_ADC) == descr->adc.Instance)) {
+                instance = (ADCName) pinmap_peripheral(pin, PinMap_ADC);  
+                adc_pins[0] = pin;
+            }
         }
     }
 
@@ -138,16 +154,27 @@ int AdvancedADC::begin(uint32_t resolution, uint32_t sample_rate, size_t n_sampl
     }
 
     // Configure ADC pins.
-    for (size_t i=0; i<n_channels; i++) {
-        // Set the alternate pin names for this ADC instance.
-        adc_pins[i] = (PinName) (adc_pins[i] | descr->pin_alt);
-        // All channels must share the same instance; if not, bail out
-        if (instance != pinmap_peripheral(adc_pins[i], PinMap_ADC)) {
-            return 0;
+    pinmap_pinout(adc_pins[0], PinMap_ADC);
+    uint8_t ch_init = 1;
+    for (size_t i=1; i<n_channels; i++) {
+        for (size_t j=0; j<AN_ARRAY_SIZE(pin_alt); j++) {
+            // Calculate alternate function pin.
+            PinName pin = (PinName) (adc_pins[i] | pin_alt[j]);
+            // Check if pin is mapped.
+            if (pinmap_find_peripheral(pin, PinMap_ADC) == NC) break;
+            // Check if pin is connected to the selected ADC.
+            if (instance == pinmap_peripheral(pin, PinMap_ADC)) {
+                pinmap_pinout(pin, PinMap_ADC);
+                adc_pins[i] = pin;
+                ch_init++;
+                break;
+            }
         }
-        pinmap_pinout(adc_pins[i], PinMap_ADC);
     }
 
+    // All channels must share the same instance; if not, bail out.
+    if (ch_init < n_channels) return 0;
+
     // Allocate DMA buffer pool.
     descr->pool = new DMABufferPool<Sample>(n_samples, n_channels, n_buffers);
     if (descr->pool == nullptr) {