| Baud Rate (set on host) | Effective Throughput (kB/s) | Notes | |-------------------------|-----------------------------|-------| | 115200 | ~12.5 | USB bulk limited by host serial layer emulation | | 921600 | ~65 | Higher setting improves throughput | | 1000000 (1M) | ~85 | Near USB FS max for single bulk endpoint |
import serial ser = serial.Serial('COM5', 115200, timeout=1) ser.write(b'Hello STM32') data = ser.read(100) print(data) 8. Common Issues and Troubleshooting | Problem | Solution | |----------------------------------|----------| | Driver install fails (code 10, 28) | Disable driver signature enforcement (temporary) or use official installer | | COM port appears but no data | Check USB cable, ensure VBUS is present, verify USB DP/DN routing | | Data loss at high speed | Implement double buffering in CDC_Receive_FS | | Linux not detecting /dev/ttyACM* | Check dmesg for CDC ACM errors; ensure modprobe cdc_acm | | macOS: "Device not configured" | Reset SMC / NVRAM, or replug after driver loads | 9. Conclusion The STMicroelectronics Virtual COM Port driver provides an elegant, low-cost solution for host-to-STM32 communication by leveraging the built-in USB peripheral. It eliminates the need for external USB-UART adapters and simplifies embedded development. While throughput is limited by USB full speed (~12 Mbps) and driver overhead, it is sufficient for debugging, firmware updates, and moderate data logging. The driver is robust across major operating systems, though Windows installation remains the most involved. Future enhancements could include USB High-Speed support (available on STM32F7/H7 series) and native cross-platform driverless operation via WebUSB. References [1] STMicroelectronics. “USB CDC Class VCP Driver for STM32.” UM1734 User Manual, 2019. [2] USB Implementers Forum. “Universal Serial Bus Class Definitions for Communications Devices,” Revision 1.1, 2007. [3] STM32CubeF4 Firmware Package. “USB_Device_Examples/Virtual_COM_Port,” STMicroelectronics, 2023. [4] Microsoft. “Serial and Parallel Port Drivers.” Windows Driver Kit documentation, 2021. [5] Linux Kernel. “CDC ACM Driver Documentation,” Documentation/usb/usb-serial.txt. Appendix A: Sample STM32CubeMX Configuration Screenshots Appendix B: Driver INF File Annotations Appendix C: Performance Test Raw Data Logs stmicroelectronics virtual com port driver
static int8_t CDC_Receive_FS(uint8_t* Buf, uint32_t *Len) | Baud Rate (set on host) | Effective
// Copy Buf to application buffer USBD_CDC_SetRxBuffer(&hUsbDeviceFS, &RxBuffer[0]); USBD_CDC_ReceivePacket(&hUsbDeviceFS); return (USBD_OK); It eliminates the need for external USB-UART adapters