[stm32l476] Wrong ADC readings #4965
Description
Hello all,
i have a custom board with an stm32l476rg. The board is battery powered, and i have a voltage sensing circuit composed by a mosfet and a voltage divider to respectively enable reading the battery voltage and bring the voltage down to acceptable levels.
For a battery at 3.77V the output of the voltage divider is 2.8V which is something i can confirm with both the multimeter and a simple adc reading using the stm32 toolchain and HAL.
If i read the same pin with embassy the readings are roughly one order of magnitude smaller. Below is the embassy code i'm using (disregard the conversion to millivolts, the constant is probably wrong).
My embassy crates are from git at commit fcd5383
There must be something i'm doing wrong but i cannot figure out what. The only glaring difference between embassy and stm is that HAL_ADCEx_Calibration_Start which i don't know how to replicate in embassy.
#![no_std]
#![no_main]
use defmt::*;
use embassy_executor::Spawner;
use embassy_stm32::adc::{Adc, SampleTime};
use embassy_stm32::gpio::{Input, Level, Output, Pull, Speed};
use embassy_time::Timer;
use {defmt_rtt as _, panic_probe as _};
#[embassy_executor::main]
async fn main(_spawner: Spawner) {
let mut config = embassy_stm32::Config::default();
{
use embassy_stm32::rcc::*;
config.rcc.mux.adcsel = mux::Adcsel::SYS;
}
let p = embassy_stm32::init(config);
info!("Hello World!");
let mut adc = Adc::new(p.ADC1);
let mut pin = p.PC1;
let mut bat_mon_en = Output::new(p.PC2, Level::High, Speed::Low);
let mut vrefint = adc.enable_vrefint();
let vrefint_sample = adc.blocking_read(&mut vrefint, SampleTime::CYCLES2_5);
let convert_to_millivolts = |sample| {
// From http://www.st.com/resource/en/datasheet/DM00273119.pdf
// 6.3.27 Reference voltage
const VREFINT_MV: u32 = 1210; // mV
(u32::from(sample) * VREFINT_MV / u32::from(vrefint_sample)) as u16
};
info!("VREFINT: raw: {}, converted: {} mV", vrefint_sample, convert_to_millivolts(vrefint_sample));
Timer::after_millis(5000).await;
loop {
let v = adc.blocking_read(&mut pin, SampleTime::CYCLES6_5);
info!("--> {} - {} mV", v, convert_to_millivolts(v));
Timer::after_millis(100).await;
}
}This code produces the following output:
0.000762 INFO VREFINT: raw: 1494, converted: 1210 mV
└─ stm_blink::____embassy_main_task::____embassy_main_task_inner_function::{async_fn#0} @ src/main.rs:36
5.001861 INFO --> 431 - 349 mV
└─ stm_blink::____embassy_main_task::____embassy_main_task_inner_function::{async_fn#0} @ src/main.rs:41
5.103057 INFO --> 452 - 366 mV
└─ stm_blink::____embassy_main_task::____embassy_main_task_inner_function::{async_fn#0} @ src/main.rs:41
5.204254 INFO --> 458 - 371 mV
└─ stm_blink::____embassy_main_task::____embassy_main_task_inner_function::{async_fn#0} @ src/main.rs:41
5.305450 INFO --> 465 - 376 mV
└─ stm_blink::____embassy_main_task::____embassy_main_task_inner_function::{async_fn#0} @ src/main.rs:41
5.406646 INFO --> 464 - 376 mV
└─ stm_blink::____embassy_main_task::____embassy_main_task_inner_function::{async_fn#0} @ src/main.rs:41
5.507843 INFO --> 459 - 371 mV
└─ stm_blink::____embassy_main_task::____embassy_main_task_inner_function::{async_fn#0} @ src/main.rs:41
The ADC output from stm's HAL is around 3400/3500 which is what i would expect.
For reference, here's the code:
/* USER CODE BEGIN Header */
/**
******************************************************************************
* @file : main.c
* @brief : Main program body
******************************************************************************
* @attention
*
* Copyright (c) 2025 STMicroelectronics.
* All rights reserved.
*
* This software is licensed under terms that can be found in the LICENSE file
* in the root directory of this software component.
* If no LICENSE file comes with this software, it is provided AS-IS.
*
******************************************************************************
*/
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"
/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
/* USER CODE END Includes */
/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */
/* USER CODE END PTD */
/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
/* USER CODE END PD */
/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */
/* USER CODE END PM */
/* Private variables ---------------------------------------------------------*/
ADC_HandleTypeDef hadc1;
I2C_HandleTypeDef hi2c1;
I2C_HandleTypeDef hi2c2;
QSPI_HandleTypeDef hqspi;
SD_HandleTypeDef hsd1;
UART_HandleTypeDef huart4;
PCD_HandleTypeDef hpcd_USB_OTG_FS;
/* USER CODE BEGIN PV */
/* USER CODE END PV */
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
void PeriphCommonClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_ADC1_Init(void);
static void MX_I2C1_Init(void);
static void MX_I2C2_Init(void);
static void MX_QUADSPI_Init(void);
//static void MX_SDMMC1_SD_Init(void);
static void MX_UART4_Init(void);
static void MX_USB_OTG_FS_PCD_Init(void);
/* USER CODE BEGIN PFP */
/* USER CODE END PFP */
/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
/* USER CODE END 0 */
/**
* @brief The application entry point.
* @retval int
*/
int main(void)
{
/* USER CODE BEGIN 1 */
/* USER CODE END 1 */
/* MCU Configuration--------------------------------------------------------*/
/* Reset of all peripherals, Initializes the Flash interface and the Systick. */
HAL_Init();
/* USER CODE BEGIN Init */
/* USER CODE END Init */
/* Configure the system clock */
SystemClock_Config();
/* Configure the peripherals common clocks */
PeriphCommonClock_Config();
/* USER CODE BEGIN SysInit */
/* USER CODE END SysInit */
/* Initialize all configured peripherals */
MX_GPIO_Init();
MX_ADC1_Init();
MX_I2C1_Init();
MX_I2C2_Init();
MX_QUADSPI_Init();
// MX_SDMMC1_SD_Init();
MX_UART4_Init();
MX_USB_OTG_FS_PCD_Init();
/* USER CODE BEGIN 2 */
uint32_t value_adc;
HAL_ADCEx_Calibration_Start(&hadc1, ADC_SINGLE_ENDED);
HAL_Delay (1500);
HAL_GPIO_WritePin(GPIOC, GPIO_PIN_2, GPIO_PIN_SET);
float adc_to_voltage(uint32_t raw)
{
const float vref = 3.3f; // your Vref+
const float max = 4095.0f; // for 12-bit
return (raw * vref) / max;
}
/* USER CODE END 2 */
/* Infinite loop */
/* USER CODE BEGIN WHILE */
while (1)
{
/* USER CODE END WHILE */
/* USER CODE BEGIN 3 */
HAL_ADC_Start(&hadc1);
// 3. Poll for conversion
// if (HAL_ADC_PollForConversion(&hadc1, 10) == HAL_OK)
{
// 4. Read value (0…4095 for 12-bit)
value_adc = HAL_ADC_GetValue(&hadc1);
}
float converted = adc_to_voltage(value_adc);
HAL_ADC_Stop(&hadc1);
}
/* USER CODE END 3 */
}
/**
* @brief System Clock Configuration
* @retval None
*/
void SystemClock_Config(void)
{
RCC_OscInitTypeDef RCC_OscInitStruct = {0};
RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
/** Configure the main internal regulator output voltage
*/
if (HAL_PWREx_ControlVoltageScaling(PWR_REGULATOR_VOLTAGE_SCALE1) != HAL_OK)
{
Error_Handler();
}
/** Initializes the RCC Oscillators according to the specified parameters
* in the RCC_OscInitTypeDef structure.
*/
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_MSI;
RCC_OscInitStruct.MSIState = RCC_MSI_ON;
RCC_OscInitStruct.MSICalibrationValue = 0;
RCC_OscInitStruct.MSIClockRange = RCC_MSIRANGE_6;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_MSI;
RCC_OscInitStruct.PLL.PLLM = 1;
RCC_OscInitStruct.PLL.PLLN = 40;
RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV7;
RCC_OscInitStruct.PLL.PLLQ = RCC_PLLQ_DIV2;
RCC_OscInitStruct.PLL.PLLR = RCC_PLLR_DIV2;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
Error_Handler();
}
/** Initializes the CPU, AHB and APB buses clocks
*/
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_4) != HAL_OK)
{
Error_Handler();
}
}
/**
* @brief Peripherals Common Clock Configuration
* @retval None
*/
void PeriphCommonClock_Config(void)
{
RCC_PeriphCLKInitTypeDef PeriphClkInit = {0};
/** Initializes the peripherals clock
*/
PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USB|RCC_PERIPHCLK_SDMMC1;
PeriphClkInit.UsbClockSelection = RCC_USBCLKSOURCE_PLLSAI1;
PeriphClkInit.Sdmmc1ClockSelection = RCC_SDMMC1CLKSOURCE_PLLSAI1;
PeriphClkInit.PLLSAI1.PLLSAI1Source = RCC_PLLSOURCE_MSI;
PeriphClkInit.PLLSAI1.PLLSAI1M = 1;
PeriphClkInit.PLLSAI1.PLLSAI1N = 24;
PeriphClkInit.PLLSAI1.PLLSAI1P = RCC_PLLP_DIV7;
PeriphClkInit.PLLSAI1.PLLSAI1Q = RCC_PLLQ_DIV2;
PeriphClkInit.PLLSAI1.PLLSAI1R = RCC_PLLR_DIV2;
PeriphClkInit.PLLSAI1.PLLSAI1ClockOut = RCC_PLLSAI1_48M2CLK;
if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)
{
Error_Handler();
}
}
/**
* @brief ADC1 Initialization Function
* @param None
* @retval None
*/
static void MX_ADC1_Init(void)
{
/* USER CODE BEGIN ADC1_Init 0 */
/* USER CODE END ADC1_Init 0 */
ADC_MultiModeTypeDef multimode = {0};
ADC_ChannelConfTypeDef sConfig = {0};
/* USER CODE BEGIN ADC1_Init 1 */
/* USER CODE END ADC1_Init 1 */
/** Common config
*/
hadc1.Instance = ADC1;
hadc1.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV8;
hadc1.Init.Resolution = ADC_RESOLUTION_12B;
hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;
hadc1.Init.ScanConvMode = ADC_SCAN_DISABLE;
hadc1.Init.EOCSelection = ADC_EOC_SINGLE_CONV;
hadc1.Init.LowPowerAutoWait = DISABLE;
hadc1.Init.ContinuousConvMode = DISABLE;
hadc1.Init.NbrOfConversion = 1;
hadc1.Init.DiscontinuousConvMode = DISABLE;
hadc1.Init.ExternalTrigConv = ADC_SOFTWARE_START;
hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
hadc1.Init.DMAContinuousRequests = DISABLE;
hadc1.Init.Overrun = ADC_OVR_DATA_PRESERVED;
hadc1.Init.OversamplingMode = DISABLE;
if (HAL_ADC_Init(&hadc1) != HAL_OK)
{
Error_Handler();
}
/** Configure the ADC multi-mode
*/
multimode.Mode = ADC_MODE_INDEPENDENT;
if (HAL_ADCEx_MultiModeConfigChannel(&hadc1, &multimode) != HAL_OK)
{
Error_Handler();
}
/** Configure Regular Channel
*/
sConfig.Channel = ADC_CHANNEL_2;
sConfig.Rank = ADC_REGULAR_RANK_1;
sConfig.SamplingTime = ADC_SAMPLETIME_2CYCLES_5;
sConfig.SingleDiff = ADC_SINGLE_ENDED;
sConfig.OffsetNumber = ADC_OFFSET_NONE;
sConfig.Offset = 0;
if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN ADC1_Init 2 */
/* USER CODE END ADC1_Init 2 */
}
/**
* @brief I2C1 Initialization Function
* @param None
* @retval None
*/
static void MX_I2C1_Init(void)
{
/* USER CODE BEGIN I2C1_Init 0 */
/* USER CODE END I2C1_Init 0 */
/* USER CODE BEGIN I2C1_Init 1 */
/* USER CODE END I2C1_Init 1 */
hi2c1.Instance = I2C1;
hi2c1.Init.Timing = 0x10D19CE4;
hi2c1.Init.OwnAddress1 = 0;
hi2c1.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
hi2c1.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
hi2c1.Init.OwnAddress2 = 0;
hi2c1.Init.OwnAddress2Masks = I2C_OA2_NOMASK;
hi2c1.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
hi2c1.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;
if (HAL_I2C_Init(&hi2c1) != HAL_OK)
{
Error_Handler();
}
/** Configure Analogue filter
*/
if (HAL_I2CEx_ConfigAnalogFilter(&hi2c1, I2C_ANALOGFILTER_ENABLE) != HAL_OK)
{
Error_Handler();
}
/** Configure Digital filter
*/
if (HAL_I2CEx_ConfigDigitalFilter(&hi2c1, 0) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN I2C1_Init 2 */
/* USER CODE END I2C1_Init 2 */
}
/**
* @brief I2C2 Initialization Function
* @param None
* @retval None
*/
static void MX_I2C2_Init(void)
{
/* USER CODE BEGIN I2C2_Init 0 */
/* USER CODE END I2C2_Init 0 */
/* USER CODE BEGIN I2C2_Init 1 */
/* USER CODE END I2C2_Init 1 */
hi2c2.Instance = I2C2;
hi2c2.Init.Timing = 0x10D19CE4;
hi2c2.Init.OwnAddress1 = 0;
hi2c2.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
hi2c2.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
hi2c2.Init.OwnAddress2 = 0;
hi2c2.Init.OwnAddress2Masks = I2C_OA2_NOMASK;
hi2c2.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
hi2c2.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;
if (HAL_I2C_Init(&hi2c2) != HAL_OK)
{
Error_Handler();
}
/** Configure Analogue filter
*/
if (HAL_I2CEx_ConfigAnalogFilter(&hi2c2, I2C_ANALOGFILTER_ENABLE) != HAL_OK)
{
Error_Handler();
}
/** Configure Digital filter
*/
if (HAL_I2CEx_ConfigDigitalFilter(&hi2c2, 0) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN I2C2_Init 2 */
/* USER CODE END I2C2_Init 2 */
}
/**
* @brief QUADSPI Initialization Function
* @param None
* @retval None
*/
static void MX_QUADSPI_Init(void)
{
/* USER CODE BEGIN QUADSPI_Init 0 */
/* USER CODE END QUADSPI_Init 0 */
/* USER CODE BEGIN QUADSPI_Init 1 */
/* USER CODE END QUADSPI_Init 1 */
/* QUADSPI parameter configuration*/
hqspi.Instance = QUADSPI;
hqspi.Init.ClockPrescaler = 255;
hqspi.Init.FifoThreshold = 1;
hqspi.Init.SampleShifting = QSPI_SAMPLE_SHIFTING_NONE;
hqspi.Init.FlashSize = 1;
hqspi.Init.ChipSelectHighTime = QSPI_CS_HIGH_TIME_1_CYCLE;
hqspi.Init.ClockMode = QSPI_CLOCK_MODE_0;
if (HAL_QSPI_Init(&hqspi) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN QUADSPI_Init 2 */
/* USER CODE END QUADSPI_Init 2 */
}
/**
* @brief SDMMC1 Initialization Function
* @param None
* @retval None
*/
static void MX_SDMMC1_SD_Init(void)
{
/* USER CODE BEGIN SDMMC1_Init 0 */
/* USER CODE END SDMMC1_Init 0 */
/* USER CODE BEGIN SDMMC1_Init 1 */
/* USER CODE END SDMMC1_Init 1 */
hsd1.Instance = SDMMC1;
hsd1.Init.ClockEdge = SDMMC_CLOCK_EDGE_RISING;
hsd1.Init.ClockBypass = SDMMC_CLOCK_BYPASS_DISABLE;
hsd1.Init.ClockPowerSave = SDMMC_CLOCK_POWER_SAVE_DISABLE;
hsd1.Init.BusWide = SDMMC_BUS_WIDE_4B;
hsd1.Init.HardwareFlowControl = SDMMC_HARDWARE_FLOW_CONTROL_DISABLE;
hsd1.Init.ClockDiv = 0;
if (HAL_SD_Init(&hsd1) != HAL_OK)
{
Error_Handler();
}
if (HAL_SD_ConfigWideBusOperation(&hsd1, SDMMC_BUS_WIDE_4B) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN SDMMC1_Init 2 */
/* USER CODE END SDMMC1_Init 2 */
}
/**
* @brief UART4 Initialization Function
* @param None
* @retval None
*/
static void MX_UART4_Init(void)
{
/* USER CODE BEGIN UART4_Init 0 */
/* USER CODE END UART4_Init 0 */
/* USER CODE BEGIN UART4_Init 1 */
/* USER CODE END UART4_Init 1 */
huart4.Instance = UART4;
huart4.Init.BaudRate = 115200;
huart4.Init.WordLength = UART_WORDLENGTH_8B;
huart4.Init.StopBits = UART_STOPBITS_1;
huart4.Init.Parity = UART_PARITY_NONE;
huart4.Init.Mode = UART_MODE_TX_RX;
huart4.Init.HwFlowCtl = UART_HWCONTROL_NONE;
huart4.Init.OverSampling = UART_OVERSAMPLING_16;
huart4.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
huart4.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
if (HAL_UART_Init(&huart4) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN UART4_Init 2 */
/* USER CODE END UART4_Init 2 */
}
/**
* @brief USB_OTG_FS Initialization Function
* @param None
* @retval None
*/
static void MX_USB_OTG_FS_PCD_Init(void)
{
/* USER CODE BEGIN USB_OTG_FS_Init 0 */
/* USER CODE END USB_OTG_FS_Init 0 */
/* USER CODE BEGIN USB_OTG_FS_Init 1 */
/* USER CODE END USB_OTG_FS_Init 1 */
hpcd_USB_OTG_FS.Instance = USB_OTG_FS;
hpcd_USB_OTG_FS.Init.dev_endpoints = 6;
hpcd_USB_OTG_FS.Init.speed = PCD_SPEED_FULL;
hpcd_USB_OTG_FS.Init.phy_itface = PCD_PHY_EMBEDDED;
hpcd_USB_OTG_FS.Init.Sof_enable = DISABLE;
hpcd_USB_OTG_FS.Init.low_power_enable = DISABLE;
hpcd_USB_OTG_FS.Init.lpm_enable = DISABLE;
hpcd_USB_OTG_FS.Init.battery_charging_enable = DISABLE;
hpcd_USB_OTG_FS.Init.use_dedicated_ep1 = DISABLE;
hpcd_USB_OTG_FS.Init.vbus_sensing_enable = DISABLE;
if (HAL_PCD_Init(&hpcd_USB_OTG_FS) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN USB_OTG_FS_Init 2 */
/* USER CODE END USB_OTG_FS_Init 2 */
}
/**
* @brief GPIO Initialization Function
* @param None
* @retval None
*/
static void MX_GPIO_Init(void)
{
GPIO_InitTypeDef GPIO_InitStruct = {0};
/* USER CODE BEGIN MX_GPIO_Init_1 */
/* USER CODE END MX_GPIO_Init_1 */
/* GPIO Ports Clock Enable */
__HAL_RCC_GPIOC_CLK_ENABLE();
__HAL_RCC_GPIOA_CLK_ENABLE();
__HAL_RCC_GPIOB_CLK_ENABLE();
__HAL_RCC_GPIOD_CLK_ENABLE();
/*Configure GPIO pin Output Level */
HAL_GPIO_WritePin(GPIOC, GPIO_PIN_2, GPIO_PIN_RESET);
/*Configure GPIO pin : PC2 */
GPIO_InitStruct.Pin = GPIO_PIN_2;
GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
GPIO_InitStruct.Pull = GPIO_PULLUP;
GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
HAL_GPIO_Init(GPIOC, &GPIO_InitStruct);
/* USER CODE BEGIN MX_GPIO_Init_2 */
/* USER CODE END MX_GPIO_Init_2 */
}
/* USER CODE BEGIN 4 */
/* USER CODE END 4 */
/**
* @brief This function is executed in case of error occurrence.
* @retval None
*/
void Error_Handler(void)
{
/* USER CODE BEGIN Error_Handler_Debug */
/* User can add his own implementation to report the HAL error return state */
__disable_irq();
while (1)
{
}
/* USER CODE END Error_Handler_Debug */
}
#ifdef USE_FULL_ASSERT
/**
* @brief Reports the name of the source file and the source line number
* where the assert_param error has occurred.
* @param file: pointer to the source file name
* @param line: assert_param error line source number
* @retval None
*/
void assert_failed(uint8_t *file, uint32_t line)
{
/* USER CODE BEGIN 6 */
/* User can add his own implementation to report the file name and line number,
ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
/* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */Here's the circuit:
