esp-idf/docs/en/api-reference/peripherals/usb_device.rst

USB Device Driver
=================

{IDF_TARGET_USB_DP_GPIO_NUM:default="20"}
{IDF_TARGET_USB_DM_GPIO_NUM:default="19"}
{IDF_TARGET_USB_EP_NUM:default="6"}
{IDF_TARGET_USB_EP_NUM_INOUT:default="5"}
{IDF_TARGET_USB_EP_NUM_IN:default="1"}

Overview
--------

The driver allows users to use {IDF_TARGET_NAME} chips to develop USB devices on a top of the TinyUSB stack. TinyUSB is integrated with ESP-IDF to provide USB features of the framework. Using this driver the chip works as a composite device supporting several USB devices simultaneously. Currently, only the Communications Device Class (CDC) type of the device with the Abstract Control Model (ACM) subclass and the Musical Instrument Digital Interface (MIDI) are supported.

TinyUSB stack is distributed via `IDF Component Registry <https://components.espressif.com/components/espressif/esp_tinyusb>`_.

Our USB-OTG implementation is limited to {IDF_TARGET_USB_EP_NUM} USB endpoints ({IDF_TARGET_USB_EP_NUM_INOUT} IN/OUT endpoints and {IDF_TARGET_USB_EP_NUM_IN} IN endpoint) - find more information in `technical reference manual <{IDF_TARGET_TRM_EN_URL}>`_.

Features
--------

- Configuration of device and string USB descriptors
- USB Serial Device (CDC-ACM)
- Input and output streams through USB Serial Device
- Other USB classes (MIDI, MSC, HID...) support directly via TinyUSB
- VBUS monitoring for self-powered devices

Hardware USB Connection
-----------------------

- Any board with the {IDF_TARGET_NAME} chip with USB connectors or with exposed USB's D+ and D- (DATA+/DATA-) pins.

If the board has no USB connector but has the pins, connect pins directly to the host (e.g. with do-it-yourself cable from any USB connection cable).

On {IDF_TARGET_NAME}, connect GPIO {IDF_TARGET_USB_DP_GPIO_NUM} and {IDF_TARGET_USB_DM_GPIO_NUM} to D+/D- respectively:


.. figure:: ../../../_static/usb-board-connection.png
    :align: center
    :alt: Connection of an ESP board to a USB host 
    :figclass: align-center

Self-powered devices must also connect VBUS through voltage divider or comparator, more details in :ref:`self-powered-device` subchapter.

Driver Structure
----------------

As the basis is used the TinyUSB stack.

On top of it the driver implements:

- Customization of USB descriptors
- Serial device support
- Redirecting of standard streams through the Serial device
- Encapsulated driver's task servicing the TinyUSB

Configuration
-------------

Via Menuconfig options you can specify:

- Several of descriptor's parameters (see: Descriptors Configuration bellow)
- USB Serial low-level Configuration
- The verbosity of the TinyUSB's log
- Disable the TinyUSB main task (for the custom implementation)

Descriptors Configuration
^^^^^^^^^^^^^^^^^^^^^^^^^

The driver's descriptors are provided by the :cpp:type:`tinyusb_config_t` structure's :cpp:member:`descriptor` and :cpp:member:`string_descriptor` members. Therefore, users should initialize :cpp:type:`tinyusb_config_t` to their desired descriptor before calling :cpp:func:`tinyusb_driver_install` to install driver.

However, the driver also provides a default descriptor. The driver can be installed with the default descriptor by setting the :cpp:member:`descriptor` and :cpp:member:`string_descriptor` members of :cpp:type:`tinyusb_config_t` to `NULL` before calling :cpp:func:`tinyusb_driver_install`. The driver's default descriptor is specified using Menuconfig, where the following fields should be configured:

- PID
- VID
- bcdDevice
- Manufacturer
- Product name
- Name of CDC device if it is On
- Serial number

If you want to use your own descriptors with extended modification, you can define them during the driver installation process.

Install Driver
--------------

To initialize the driver, users should call :cpp:func:`tinyusb_driver_install`. The driver's configuration is specified in a :cpp:type:`tinyusb_config_t` structure that is passed as an argument to :cpp:func:`tinyusb_driver_install`.

 Note that the :cpp:type:`tinyusb_config_t` structure can be zero initialized (e.g. ``tinyusb_config_t tusb_cfg = { 0 }``) or partially (as shown below). For any member that is initialized to `0` or `NULL`, the driver will use its default configuration values for that member (see example below)

.. code-block:: c

    const tinyusb_config_t partial_init = {
        .descriptor = NULL;         //Uses default descriptor specified in Menuconfig
        .string_descriptor = NULL;  //Uses default string specified in Menuconfig
        .external_phy = false;
    };

.. _self-powered-device:

Self-Powered Device
-------------------

USB specification mandates self-powered devices to monitor voltage level on USB's VBUS signal. As opposed to bus-powered devices, a self-powered device can be fully functional even without USB connection. The self-powered device detects connection and disconnection events by monitoring the VBUS voltage level. VBUS is considered valid if it rises above 4.75V and invalid if it falls below 4.35V.

No {IDF_TARGET_NAME} pin is 5V tolerant, so you must connect the VBUS to {IDF_TARGET_NAME} via a comparator with voltage thresholds as described above, or use a simple resistor voltage divider that will output (0.75 x Vdd) if VBUS is 4.4V (see figure below). In both cases, voltage on the sensing pin must be logic low within 3ms after the device is unplugged from USB host.

.. figure:: ../../../_static/diagrams/usb/usb_vbus_voltage_monitor.png
    :align: center
    :alt: Simple voltage divider for VBUS monitoring
    :figclass: align-center

    Simple voltage divider for VBUS monitoring

To use this feature, in :cpp:type:`tinyusb_config_t` you must set :cpp:member:`self_powered` to ``true`` and :cpp:member:`vbus_monitor_io` to GPIO number that will be used for VBUS monitoring.

USB Serial Device (CDC-ACM)
---------------------------

If the CDC option is enabled in Menuconfig, the USB Serial Device could be initialized with :cpp:func:`tusb_cdc_acm_init` according to the settings from :cpp:type:`tinyusb_config_cdcacm_t` (see example below).

.. code-block:: c

    tinyusb_config_cdcacm_t acm_cfg = {
        .usb_dev = TINYUSB_USBDEV_0,
        .cdc_port = TINYUSB_CDC_ACM_0,
        .rx_unread_buf_sz = 64,
        .callback_rx = NULL,
        .callback_rx_wanted_char = NULL,
        .callback_line_state_changed = NULL,
        .callback_line_coding_changed = NULL
    };
    tusb_cdc_acm_init(&acm_cfg);

To specify callbacks you can either set the pointer to your :cpp:type:`tusb_cdcacm_callback_t` function in the configuration structure or call :cpp:func:`tinyusb_cdcacm_register_callback` after initialization.

USB Serial Console
^^^^^^^^^^^^^^^^^^

The driver allows to redirect all standard application streams (stdinm stdout, stderr) to the USB Serial Device and return them to UART using :cpp:func:`esp_tusb_init_console`/:cpp:func:`esp_tusb_deinit_console` functions.

Application Examples
--------------------

The table below describes the code examples available in the directory :example:`peripherals/usb/`.

.. list-table::
   :widths: 35 65
   :header-rows: 1

   * - Code Example
     - Description
   * - :example:`peripherals/usb/device/tusb_console`
     - How to set up {IDF_TARGET_NAME} chip to get log output via Serial Device connection
   * - :example:`peripherals/usb/device/tusb_serial_device`
     - How to set up {IDF_TARGET_NAME} chip to work as a USB Serial Device
   * - :example:`peripherals/usb/device/tusb_midi`
     - How to set up {IDF_TARGET_NAME} chip to work as a USB MIDI Device
   * - :example:`peripherals/usb/device/tusb_hid`
     - How to set up {IDF_TARGET_NAME} chip to work as a USB Human Interface Device