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******************
Your First USB Host
******************
This tutorial guides you through creating a simple USB host application that can connect to and communicate with USB devices.
Prerequisites
=============
* Completed :doc:`getting_started` and :doc:`first_device` tutorials
* Development board with USB host capability (e.g., STM32F4 Discovery with USB-A connector)
* USB device to test with (USB drive, mouse, keyboard, or CDC device)
Understanding USB Host Basics
=============================
A USB host application needs:
1. **Device Enumeration**: Detect and configure connected devices
2. **Class Drivers**: Handle communication with specific device types
3. **Application Logic**: Process data from/to the connected devices
Step 1: Start with an Example
=============================
Use the ``cdc_msc_hid`` host example:
.. code-block:: bash
cd examples/host/cdc_msc_hid
This example can communicate with CDC (serial), MSC (storage), and HID (keyboard/mouse) devices.
Step 2: Understand the Code Structure
=====================================
Key components:
* ``main.c`` - Main loop and device event handling
* Host callbacks - Functions called when devices connect/disconnect
* Class-specific handlers - Process data from different device types
**Main Loop Pattern**:
.. code-block:: c
int main(void) {
board_init();
tusb_init();
while (1) {
tuh_task(); // TinyUSB host task
// Handle connected devices
}
}
**Connection Events**: TinyUSB calls your callbacks when devices connect:
.. code-block:: c
void tuh_mount_cb(uint8_t dev_addr) {
printf("Device connected, address = %d\\n", dev_addr);
}
void tuh_umount_cb(uint8_t dev_addr) {
printf("Device disconnected, address = %d\\n", dev_addr);
}
Step 3: Build and Test
======================
.. code-block:: bash
# Fetch dependencies
python ../../../tools/get_deps.py stm32f4
# Build
make BOARD=stm32f407disco all
# Flash
make BOARD=stm32f407disco flash
**Testing**: Connect different USB devices and observe the output via serial console.
Step 4: Handle Specific Device Types
====================================
**Mass Storage (USB Drive)**:
.. code-block:: c
void tuh_msc_mount_cb(uint8_t dev_addr) {
printf("USB Drive mounted\\n");
// Read/write files
}
**HID Devices (Keyboard/Mouse)**:
.. code-block:: c
void tuh_hid_mount_cb(uint8_t dev_addr, uint8_t instance,
uint8_t const* desc_report, uint16_t desc_len) {
uint8_t const itf_protocol = tuh_hid_interface_protocol(dev_addr, instance);
if (itf_protocol == HID_ITF_PROTOCOL_KEYBOARD) {
printf("Keyboard connected\\n");
}
}
**CDC Devices (Serial)**:
.. code-block:: c
void tuh_cdc_mount_cb(uint8_t idx) {
printf("CDC device mounted\\n");
// Configure serial settings
tuh_cdc_set_baudrate(idx, 115200, NULL, 0);
}
Common Issues and Solutions
===========================
**No Device Detection**:
* Check power supply - host mode requires more power than device mode
* Verify USB connector wiring and type (USB-A for host vs USB micro/C for device)
* Enable logging with ``LOG=2`` to see enumeration process
**Enumeration Failures**:
* Some devices need more time - increase timeouts
* Check USB hub support if using a hub
* Verify device is USB 2.0 compatible (USB 3.0 devices should work in USB 2.0 mode)
**Class Driver Issues**:
* Not all devices follow standards perfectly - may need custom handling
* Check device descriptors with USB analyzer tools
* Some composite devices may not be fully supported
Hardware Considerations
=======================
**Power Requirements**:
* Host mode typically requires external power or powered USB hub
* Check board documentation for power limitations
* Some boards need jumper changes to enable host power
**Pin Configuration**:
* Host and device modes often use different USB connectors/pins
* Verify board supports host mode on your chosen port
* Check if OTG (On-The-Go) configuration is needed
Next Steps
==========
* Learn about supported USB classes in :doc:`../reference/usb_classes`
* Understand advanced integration in :doc:`../guides/integration`
* Explore TinyUSB architecture in :doc:`../explanation/architecture`
|
