How do you implement USB communication on STM32?

 

USB Communication Implementation on STM32 (Step-by-Step Guide)

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1. Hardware Setup

Required Components:

• STM32 with USB peripheral (e.g., STM32F4xx, STM32H7xx)

• USB connector (Type-C/Micro-B) + pull-up resistors (1.5kΩ on DP for Full Speed)

• VBUS detection circuit (optional but recommended)

Pin Connections:

STM32 Pin	USB Signal	Description
PA11	DM (D-)	Data Minus
PA12	DP (D+)	Data Plus
VBUS	5V Input	Power Sensing (if used)

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2. Software Configuration (Using STM32CubeIDE)

Step 1: Enable USB in CubeMX

1. Open STM32CubeMX → Select your MCU

2. Enable USB (OTG_FS or OTG_HS) under "Connectivity"

3. Set mode:

   • Device Mode (for USB CDC/HID/Mass Storage)

   • Host Mode (for connecting to peripherals)

4. Configure Clock Settings:

   • Ensure 48MHz clock to USB peripheral (PLL must generate this)

Step 2: Select Middleware (USB Classes)

• CDC (Virtual COM Port): For serial communication

• HID: For keyboards/mice

• MSC (Mass Storage): For USB drives

• Custom Class: For vendor-specific protocols

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3. Example: USB CDC (Virtual COM Port)

Code Implementation:

c

// 1. Initialize USB (generated by CubeMX)
MX_USB_DEVICE_Init();

// 2. Send Data via USB CDC
uint8_t data[] = "Hello USB!\r\n";
CDC_Transmit_FS(data, sizeof(data));

// 3. Receive Data (callback)
void HAL_CDC_Receive_FS(uint8_t* Buf, uint32_t *Len) {
  // Process received data (e.g., echo back)
  CDC_Transmit_FS(Buf, *Len);
}

Descriptor Configuration (in usbd_cdc.c):

c

// Modify USB VID/PID (optional)
#define USBD_VID     0x0483  // STM's VID
#define USBD_PID     0x5740  // Custom PID

// Adjust endpoint sizes (default is 64 bytes)
#define CDC_DATA_FS_MAX_PACKET_SIZE  64

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4. USB HID Example (Mouse Emulator)

c

// 1. Define HID report descriptor (in usbd_hid.c)
__ALIGN_BEGIN static uint8_t HID_MOUSE_ReportDesc[] __ALIGN_END = {
  0x05, 0x01,  // USAGE_PAGE (Generic Desktop)
  0x09, 0x02,  // USAGE (Mouse)
  // ... (see USB HID specs)
};

// 2. Send mouse movement
uint8_t report[4] = {0, dx, dy, 0};  // Buttons, X, Y, Wheel
USBD_HID_SendReport(&hUsbDeviceFS, report, sizeof(report));

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5. Debugging Tips

Common Issues & Fixes:

Symptom	Likely Cause	Solution
USB not detected	Missing pull-up on DP	Add 1.5kΩ resistor to 3.3V
Enumeration fails	Incorrect clock/PLL config	Verify 48MHz USB clock
Data corruption	Buffer overflow	Check endpoint sizes

Debug Tools:

• USBlyzer/Wireshark: Monitor USB traffic

• ST-Link Debugger: Breakpoint analysis

• USB Descriptor Validator: Check descriptor compliance

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6. Advanced Topics

Dual-Role (OTG) Setup:

c

// Enable OTG mode in CubeMX
USB_OTG_FS->GUSBCFG |= USB_OTG_GUSBCFG_FDMOD;  // Force Device Mode

USB DFU (Firmware Update):

1. Set BOOT0=1 to enter DFU mode

2. Use dfu-util to flash .dfu files:

   bash

   
   

   dfu-util -d 0483:df11 -a 0 -s 0x08000000 -D firmware.dfu

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7. Example Projects

1. USB-to-UART Bridge (CDC):

   • Forward data between USB and UART (e.g., STM32 as a COM port)

2. Custom HID Device:

   • Send sensor data (e.g., accelerometer) as HID reports

3. USB Audio Interface:

   • Use USB Audio Class (UAC) for microphone/speaker