Hey, I have a custom STM32F407 based board with USB.
USB_P is connected to PA12
USB_N is connected to PA11
In the STM32CubeMX I have configured USB Device and in the middleclass I have enabled Communication Device Class (Virtual Port Com) for the Class for FS IP.
My main.c 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"
#include "usb_device.h"
/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include "printf.h"
#include "scpi/scpi.h"
#include "scpi-def.h"
#include "usbd_cdc_if.h"
/* 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 ---------------------------------------------------------*/
UART_HandleTypeDef huart4;
/* USER CODE BEGIN PV */
extern uint8_t UserRxBufferFS[APP_RX_DATA_SIZE];
extern uint8_t UserTxBufferFS[APP_TX_DATA_SIZE];
extern uint8_t is_new_data_ready;
extern uint16_t new_data_length;
/* USER CODE END PV */
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_UART4_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();
/* USER CODE BEGIN SysInit */
/* USER CODE END SysInit */
/* Initialize all configured peripherals */
MX_GPIO_Init();
MX_UART4_Init();
MX_USB_DEVICE_Init();
/* USER CODE BEGIN 2 */
SCPI_Init(&scpi_context,
scpi_commands,
&scpi_interface,
scpi_units_def,
SCPI_IDN1, SCPI_IDN2, SCPI_IDN3, SCPI_IDN4,
scpi_input_buffer, SCPI_INPUT_BUFFER_LENGTH,
scpi_error_queue_data, SCPI_ERROR_QUEUE_SIZE);
printf("Hello from ST32F407 \n");
/* USER CODE END 2 */
/* Infinite loop */
/* USER CODE BEGIN WHILE */
while (1)
{
/* USER CODE END WHILE */
/* USER CODE BEGIN 3 */
if (is_new_data_ready) {
SCPI_Input(&scpi_context, UserRxBufferFS, new_data_length);
is_new_data_ready = 0;
}
}
/* 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
*/
__HAL_RCC_PWR_CLK_ENABLE();
__HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);
/** Initializes the RCC Oscillators according to the specified parameters
* in the RCC_OscInitTypeDef structure.
*/
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI|RCC_OSCILLATORTYPE_HSE;
RCC_OscInitStruct.HSEState = RCC_HSE_ON;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
RCC_OscInitStruct.PLL.PLLM = 4;
RCC_OscInitStruct.PLL.PLLN = 72;
RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
RCC_OscInitStruct.PLL.PLLQ = 3;
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_HSI;
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_0) != HAL_OK)
{
Error_Handler();
}
}
/**
* @brief UART4 Initialization Function
* 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;
if (HAL_UART_Init(&huart4) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN UART4_Init 2 */
/* USER CODE END UART4_Init 2 */
}
/**
* @brief GPIO Initialization Function
* None
* @retval None
*/
static void MX_GPIO_Init(void)
{
/* 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_GPIOH_CLK_ENABLE();
__HAL_RCC_GPIOA_CLK_ENABLE();
/* 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.
* file: pointer to the source file name
* 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 */
For handling USB data, I have ported the code from the github repository:
https://github.com/Jana-Marie/stm32g4xx_usb_cdc
The USB communication seem to work fine - I can send and receive data via the USB Virtual com port:
Since this is my first time dealing with USB, I have decided to hook up my Saleae logic analyzer to usb D+ and D- pins to inspect how it works and what it sends.
This is my Analyzer configuration:
But I am very confused about USB decode level, what should I choose?
And I notice things I did not expect to see. When I have the virtual com port disabled (not connected), I see the following:
If I zoom in, I see the following:
As soon as I open the com port, I see the following:
If I zoom in, it looks as following:
When I try to send data via com port, I get the expected response:
MEASure:VOLTage:DC:OUTput?
1337
MEASure:VOLTage:DC:OUTput?
1337
MEASure:VOLTage:DC:OUTput?
1337
MEASure:VOLTage:DC:OUTput?
1337
MEASure:VOLTage:DC:OUTput?
1337
But I cannot make anything out from the D- and D+ lines when sending/receiving.
I want to understand whether this behaviour is normal.
