How do you set up LPUART1 with an STM32L452RE?

[RBamf.1]

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

[gbm]

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]

> 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?