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How do you set up LPUART1 with an STM32L452RE?

RBamf.1
Associate III

Hi i'm trying to get the LPUART (PA3, PA2) pins to communicate with my computer via the serial port, but i can't get anything to work. Here is what i'm trying to use at the moment...

Sysclock Config:

#pragma once
 
extern "C" void SystemClock_Config(void)
{
    RCC_OscInitTypeDef RCC_OscInitStruct = {};
    RCC_ClkInitTypeDef RCC_ClkInitStruct = {};
    RCC_PeriphCLKInitTypeDef PeriphClkInit = { 0 };
 
    /* Configure LSE Drive Capability */
    HAL_PWR_EnableBkUpAccess();
    __HAL_RCC_LSEDRIVE_CONFIG(RCC_LSEDRIVE_LOW);
 
    /* Initializes the CPU, AHB and APB busses clocks */
    RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_LSE | RCC_OSCILLATORTYPE_MSI;
    RCC_OscInitStruct.LSEState = RCC_LSE_ON;
    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 busses 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();
    }
 
    PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_LPUART1 | RCC_PERIPHCLK_SAI1
        | RCC_PERIPHCLK_SDMMC1;
    PeriphClkInit.Sdmmc1ClockSelection = RCC_SDMMC1CLKSOURCE_PLLSAI1;
    PeriphClkInit.Sai1ClockSelection = RCC_LPUART1CLKSOURCE_PCLK1;
    PeriphClkInit.Lpuart1ClockSelection =RCC_LPUART1CLKSOURCE_PCLK1;
    PeriphClkInit.PLLSAI1.PLLSAI1Source = RCC_PLLSOURCE_MSI;
    PeriphClkInit.PLLSAI1.PLLSAI1M = 1;
    PeriphClkInit.PLLSAI1.PLLSAI1N = 16;
    PeriphClkInit.PLLSAI1.PLLSAI1P = RCC_PLLP_DIV17;
    PeriphClkInit.PLLSAI1.PLLSAI1Q = RCC_PLLQ_DIV4;
    PeriphClkInit.PLLSAI1.PLLSAI1R = RCC_PLLR_DIV2;
    PeriphClkInit.PLLSAI1.PLLSAI1ClockOut = RCC_PLLSAI1_SAI1CLK | RCC_PLLSAI1_ADC1CLK;
 
    if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK) {
        Error_Handler();
    }
 
    /* Configure the main internal regulator output voltage */
    if (HAL_PWREx_ControlVoltageScaling(PWR_REGULATOR_VOLTAGE_SCALE1) != HAL_OK) {
        Error_Handler();
    }
 
    /* Enable MSI Auto calibration */
    HAL_RCCEx_EnableMSIPLLMode();
}

Main.c

UART_HandleTypeDef hlpuart1;
uint8_t aTxBuffer[14] = "Hello World\r\n";
 
void setup()
{
    GPIO_InitTypeDef GPIO_InitStruct = { 0 };
 
    __HAL_RCC_LPUART1_CLK_ENABLE();
 
    __HAL_RCC_GPIOA_CLK_ENABLE();
 
    /**LPUART1 GPIO Configuration
    PA2     ------> LPUART1_TX
    PA3     ------> LPUART1_RX
    */
    GPIO_InitStruct.Pin = GPIO_PIN_2 | GPIO_PIN_3;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF8_LPUART1;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
 
    hlpuart1.Instance = LPUART1;
    hlpuart1.Init.BaudRate = 9600;
    hlpuart1.Init.WordLength = UART_WORDLENGTH_8B;
    hlpuart1.Init.StopBits = UART_STOPBITS_1;
    hlpuart1.Init.Parity = UART_PARITY_NONE;
    hlpuart1.Init.Mode = UART_MODE_TX_RX;
    hlpuart1.Init.HwFlowCtl = UART_HWCONTROL_NONE;
    hlpuart1.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
    hlpuart1.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
    HAL_UART_Init(&hlpuart1);
}
 
int counter = 0;
void loop()
{
    HAL_UART_Transmit(&hlpuart1, (uint8_t*)aTxBuffer, 13, 5000);
    HAL_Delay(1000);
}

Can anyone help me spot whats might be causing it not to work?

Thank you very much for your time - R

2 REPLIES 2
gbm
Lead II

Me? I first look at the Reference Manual, esp. LPUART registers, then write 2 lines of code for enabling the peripherals, two assignments for UART pin assignment, then 2..3 lines for UART setup, then 6 lines of SysTick_Handler to send a character every second. When this works, I continue with some useful transmit routines.

Oh, wait... What is setup() and loop()? How are these routines called?

Bob S
Principal

> but i can't get anything to work

What exactly does that mean? What have you checked? Does HAL_UART_Transmit() return an error? Have you put a scope on the TX pin to see what is there? How do you have the STM32 UART connected to your PC?