analogout: STM32: analogout_free implementation for STM32F7

Implemented analogout_free for STM32F7 Series.

Author: AnishKumarHCL

targets/TARGET_STM/TARGET_STM32F7/analogout_device.c

@@ -35,6 +35,12 @@
 #include "stm32f7xx_hal.h"
 #include "PeripheralPins.h"
 
+// These variables are used for the "free" function
+static int channel1_used = 0;
+#if defined(DAC_CHANNEL_2)
+static int channel2_used = 0;
+#endif
+
 void analogout_init(dac_t *obj, PinName pin)
 {
     DAC_ChannelConfTypeDef sConfig = {0};
@@ -67,6 +73,9 @@ void analogout_init(dac_t *obj, PinName pin)
     // Configure GPIO
     pinmap_pinout(pin, PinMap_DAC);
 
+   // Save the pin for future use
+    obj->pin = pin;
+
     __GPIOA_CLK_ENABLE();
 
     __DAC_CLK_ENABLE();
@@ -85,12 +94,41 @@ void analogout_init(dac_t *obj, PinName pin)
         error("HAL_DAC_ConfigChannel failed");
     }
 
+    if (obj->channel == DAC_CHANNEL_1) {
+        channel1_used = 1;
+    }
+#if defined(DAC_CHANNEL_2)
+    if (obj->channel == DAC_CHANNEL_2) {
+        channel2_used = 1;
+    }
+#endif
     analogout_write_u16(obj, 0);
     HAL_DAC_Start(&obj->handle, obj->channel);
 }
 
 void analogout_free(dac_t *obj)
 {
+    if (obj->channel == DAC_CHANNEL_1) {
+        channel1_used = 0;
+    }
+#if defined(DAC_CHANNEL_2)
+    if (obj->channel == DAC_CHANNEL_2) {
+        channel2_used = 0;
+    }
+#endif
+    if ((channel1_used == 0)
+#if defined(DAC_CHANNEL_2)
+        && (channel2_used == 0)
+#endif
+        ) {
+        // Reset DAC and disable clock
+        __HAL_RCC_DAC_FORCE_RESET();
+        __HAL_RCC_DAC_RELEASE_RESET();
+        __HAL_RCC_DAC_CLK_DISABLE();
+
+        // Configure GPIO back to reset value
+        pin_function(obj->pin, STM_PIN_DATA(STM_MODE_ANALOG, GPIO_NOPULL, 0));
+    }
 }
 
 const PinMap *analogout_pinmap()