feat(stm32): Add STM32 ADC support to AnalogBatteryLevel (#9369)

Integrate STM32 battery monitoring into AnalogBatteryLevel, supporting
external GPIO ADC pins as well as internal VBAT channel.

Features:
- ADC reading using STM32 LL (Lower Layer) macros supporting external
  ADC channels and internal VBAT channel (AVBAT)
- ADC compensation using STM32 LL macros with factory-calibrated VREFINT
  (AVREF) for accurate voltage measurement
- LFP battery OCV curve for STM32WL using AVBAT (STM32 VDD absolute
  maximum supply voltage 3.9V, direct connection of Li-Po batteries is
  not supported)

Internal VBAT channel implemented in:
- Russell
- RAK3172

In these variants, ADC_MULTIPLIER = (1.01f * 3) = 3.30 as there is a
3:1 internal divider (DS13105 Rev 12 §5.3.21), and a bit of tolerance
as the actual 10% spec leads to readings much too high.


Assisted-by: Claude:sonnet-4-5

Signed-off-by: Andrew Yong <me@ndoo.sg>

src/Power.cpp

@@ -40,6 +40,22 @@
 #include "concurrency/LockGuard.h"
 #endif
 
+#if defined(ARCH_STM32WL) && defined(BATTERY_PIN)
+#include "stm32yyxx_ll_adc.h"
+
+/* Analog read resolution */
+#if defined(LL_ADC_RESOLUTION_12B)
+#define LL_ADC_RESOLUTION LL_ADC_RESOLUTION_12B
+#define BATTERY_SENSE_RESOLUTION_BITS 12
+#elif defined(LL_ADC_DS_DATA_WIDTH_12_BIT)
+#define LL_ADC_RESOLUTION LL_ADC_DS_DATA_WIDTH_12_BIT
+#define BATTERY_SENSE_RESOLUTION_BITS 12
+#else
+#error "ADC resolution could not be defined!"
+#endif
+#define ADC_RANGE (1 << BATTERY_SENSE_RESOLUTION_BITS)
+#endif
+
 #if defined(DEBUG_HEAP_MQTT) && !MESHTASTIC_EXCLUDE_MQTT
 #include "mqtt/MQTT.h"
 #include "target_specific.h"
@@ -328,11 +344,17 @@ class AnalogBatteryLevel : public HasBatteryLevel
             float scaled = 0;
 
             battery_adcEnable();
-#ifdef ARCH_ESP32 // ADC block for espressif platforms
+#ifdef ARCH_STM32WL
+            // STM32 ADC with VREFINT runtime calibration
+            Vref = __LL_ADC_CALC_VREFANALOG_VOLTAGE(analogRead(AVREF), LL_ADC_RESOLUTION);
+            raw = analogRead(BATTERY_PIN);
+            scaled = __LL_ADC_CALC_DATA_TO_VOLTAGE(Vref, raw, LL_ADC_RESOLUTION);
+            scaled *= operativeAdcMultiplier;
+#elif defined(ARCH_ESP32) // ADC block for espressif platforms
             raw = espAdcRead();
             scaled = esp_adc_cal_raw_to_voltage(raw, adc_characs);
             scaled *= operativeAdcMultiplier;
-#else // block for all other platforms
+#else                     // block for all other platforms
 #ifdef ARCH_NRF52
             concurrency::LockGuard saadcGuard(concurrency::nrf52SaadcLock);
 #endif
@@ -530,6 +552,11 @@ class AnalogBatteryLevel : public HasBatteryLevel
     bool initial_read_done = false;
     float last_read_value = (OCV[NUM_OCV_POINTS - 1] * NUM_CELLS);
     uint32_t last_read_time_ms = 0;
+#ifdef ARCH_STM32WL
+    // 3300mV placeholder for STM32 errata where VREFINT factory calibration may be missing
+    // (e.g. STM32U0, see DS14756 Rev 3 §2.4.1 "VREFINT offset")
+    uint32_t Vref = 3300;
+#endif
 
 #if HAS_TELEMETRY && !MESHTASTIC_EXCLUDE_ENVIRONMENTAL_SENSOR && defined(HAS_RAKPROT)
 
@@ -639,7 +666,9 @@ bool Power::analogInit()
 #define BATTERY_SENSE_RESOLUTION_BITS 10
 #endif
 
-#ifdef ARCH_ESP32 // ESP32 needs special analog stuff
+#ifdef ARCH_STM32WL
+    analogReadResolution(BATTERY_SENSE_RESOLUTION_BITS);
+#elif defined(ARCH_ESP32) // ESP32 needs special analog stuff
 
 #ifndef ADC_WIDTH // max resolution by default
     static const adc_bits_width_t width = ADC_WIDTH_BIT_12;
@@ -649,7 +678,7 @@ bool Power::analogInit()
 #ifndef BAT_MEASURE_ADC_UNIT // ADC1
     adc1_config_width(width);
     adc1_config_channel_atten(adc_channel, atten);
-#else // ADC2
+#else                        // ADC2
     adc2_config_channel_atten(adc_channel, atten);
 #ifndef CONFIG_IDF_TARGET_ESP32S3
     // ADC2 wifi bug workaround
@@ -679,7 +708,7 @@ bool Power::analogInit()
 
     // NRF52 ADC init moved to powerHAL_init in nrf52 platform
 
-#ifndef ARCH_ESP32
+#if !defined(ARCH_ESP32) && !defined(ARCH_STM32WL)
     analogReadResolution(BATTERY_SENSE_RESOLUTION_BITS);
 #endif