Configure USB Device and Host Modes in Hardware
- Ensure the microcontroller supports USB On-The-Go (OTG) if you need both device and host capabilities. Check the data sheet for USB features and pin configurations.
- Connect the Data (D+ and D-) lines correctly and include the necessary pull-up (for device mode) or pull-down (for host mode) resistors as specified in your hardware manual.
Enable USB Peripheral in Firmware
- Consult your microcontroller's reference manual and enable the USB peripheral clock through the System Clock Control (SYSCFG) or Clock Control Register (CCR).
- Set up USB function and power attributes in the device configuration. This usually involves setting specific registers to change the USB mode, such as the OTG_FS_GCCFG in STM32 or a similar register in other microcontrollers.
// Example for STM32 using HAL library
__HAL_RCC_USB_OTG_FS_CLK_ENABLE();
USB_OTG_FS->GCCFG |= USB_OTG_GCCFG_VBUSBSEN;
Implement USB Device Mode
- Initialize the USB stack. Many vendors provide a software library to streamline this process, such as STM32CubeMX for STM32 MCUs or Microchip's MPLAB Harmony.
- Define the USB Device Descriptor, Configuration Descriptor, and Interface Descriptors. These descriptors are necessary for host devices to understand and communicate with your USB device.
// Define USB Device Descriptor
const uint8_t USB_DeviceDescriptor[] = {
0x12, // bLength
USB_DESC_TYPE_DEVICE,
0x10, 0x01, // bcdUSB
// Add remaining descriptor fields
};
Set Up USB Host Mode
- Configure the USB Host Library stack similar to the device setup. Set the necessary power settings if the device can supply bus power.
- Handle the USB Enumeration Process. This step involves detecting when a device is attached, reading its descriptors, and setting it up according to its class (e.g., Human Interface Device, Mass Storage).
// Example enumeration handling
void USBH_OnEvent(USBH_HandleTypeDef *handle, USBH_StatusTypeDef event)
{
switch(event)
{
case HOST_USER_CONNECTION:
// Handle device connection
break;
case HOST_USER_DISCONNECTION:
// Handle device disconnection
break;
}
}
Implement USB Communication
- In Device Mode, manage data through endpoint communication. Typically, this includes endpoints 0 for control, and other endpoints for bulk transfer, interrupt, or isochronous data transfer based on the class.
- In Host Mode, send and receive data using USB transfer requests. This involves creating the appropriate USB packets and handling responses from the device.
// Example for sending data in Bulk endpoint
USBD_CtlSendData(&usbDeviceHandle, dataBuffer, dataLength);
Debug and Test your Implementation
- Use a USB protocol analyzer to capture and analyze the USB packets exchanged between the host and the device to ensure proper communication.
- Test on multiple devices and operating systems to ensure compatibility and correct functionality of both USB Host and Device Implementations.
