stm32/adc: Deselect VBAT after reading to prevent battery drain.

Signed-off-by: Damien George <damien@micropython.org>

ports/stm32/adc.c

@@ -380,16 +380,14 @@ STATIC uint32_t adc_config_and_read_channel(ADC_HandleTypeDef *adcHandle, uint32
     adc_config_channel(adcHandle, channel);
     uint32_t raw_value = adc_read_channel(adcHandle);
 
-    #if defined(STM32F4) || defined(STM32F7)
     // ST docs say that (at least on STM32F42x and STM32F43x), VBATE must
     // be disabled when TSVREFE is enabled for TEMPSENSOR and VREFINT
     // conversions to work.  VBATE is enabled by the above call to read
     // the channel, and here we disable VBATE so a subsequent call for
     // TEMPSENSOR or VREFINT works correctly.
-    if (channel == ADC_CHANNEL_VBAT) {
-        ADC->CCR &= ~ADC_CCR_VBATE;
-    }
-    #endif
+    // It's also good to disable the VBAT switch to prevent battery drain,
+    // so disable it for all MCUs.
+    adc_deselect_vbat(adcHandle->Instance, channel);
 
     return raw_value;
 }

ports/stm32/adc.h

@@ -29,4 +29,35 @@
 extern const mp_obj_type_t pyb_adc_type;
 extern const mp_obj_type_t pyb_adc_all_type;
 
+#if defined(ADC_CHANNEL_VBAT)
+
+static inline void adc_deselect_vbat(ADC_TypeDef *adc, uint32_t channel) {
+    (void)adc;
+
+    if (channel == ADC_CHANNEL_VBAT) {
+        ADC_Common_TypeDef *adc_common;
+
+        #if defined(STM32F0) || defined(STM32WB)
+        adc_common = ADC1_COMMON;
+        #elif defined(STM32F4) || defined(STM32L4)
+        adc_common = ADC_COMMON_REGISTER(0);
+        #elif defined(STM32F7)
+        adc_common = ADC123_COMMON;
+        #elif defined(STM32H7)
+        adc_common = adc == ADC3 ? ADC3_COMMON : ADC12_COMMON;
+        #endif
+
+        adc_common->CCR &= ~LL_ADC_PATH_INTERNAL_VBAT;
+    }
+}
+
+#else
+
+static inline void adc_deselect_vbat(ADC_TypeDef *adc, uint32_t channel) {
+    (void)adc;
+    (void)channel;
+}
+
+#endif
+
 #endif // MICROPY_INCLUDED_STM32_ADC_H

ports/stm32/boards/stm32f4xx_hal_conf_base.h

@@ -53,6 +53,7 @@
 #include "stm32f4xx_hal_uart.h"
 #include "stm32f4xx_hal_usart.h"
 #include "stm32f4xx_hal_wwdg.h"
+#include "stm32f4xx_ll_adc.h"
 #include "stm32f4xx_ll_rtc.h"
 
 // Enable various HAL modules

ports/stm32/boards/stm32f7xx_hal_conf_base.h

@@ -53,6 +53,7 @@
 #include "stm32f7xx_hal_uart.h"
 #include "stm32f7xx_hal_usart.h"
 #include "stm32f7xx_hal_wwdg.h"
+#include "stm32f7xx_ll_adc.h"
 #include "stm32f7xx_ll_rtc.h"
 
 // Enable various HAL modules

ports/stm32/machine_adc.c

@@ -26,6 +26,7 @@
 
 #include "py/runtime.h"
 #include "py/mphal.h"
+#include "adc.h"
 
 #if defined(STM32F0) || defined(STM32H7) || defined(STM32L0) || defined(STM32L4) || defined(STM32WB)
 #define ADC_V2 (1)
@@ -335,10 +336,15 @@ STATIC uint32_t adc_config_and_read_u16(ADC_TypeDef *adc, uint32_t channel, uint
         return 0xffff;
     }
 
+    // Select, configure and read the channel.
     adc_config_channel(adc, channel, sample_time);
     uint32_t raw = adc_read_channel(adc);
+
+    // If VBAT was sampled then deselect it to prevent battery drain.
+    adc_deselect_vbat(adc, channel);
+
+    // Scale raw reading to 16 bit value using a Taylor expansion (for bits <= 16).
     uint32_t bits = adc_get_bits(adc);
-    // Scale raw reading to 16 bit value using a Taylor expansion (for 8 <= bits <= 16)
     #if defined(STM32H7)
     if (bits < 8) {
         // For 6 and 7 bits