The ESP-IDF USB Device Stack (hereinafter referred to as the Device Stack) enables USB Device support on {IDF_TARGET_NAME}. By using the Device Stack, {IDF_TARGET_NAME} can be programmed with any well defined USB device functions (e.g., keyboard, mouse, camera), a custom function (aka vendor-specific class), or a combination of those functions (aka a composite device).
The Device Stack is built around the TinyUSB stack, but extends TinyUSB with some minor features and modifications for better integration with ESP-IDF. The Device stack is distributed as a managed component via the `ESP Component Registry <https://components.espressif.com/components/espressif/esp_tinyusb>`__.
The {IDF_TARGET_NAME} routes the USB D+ and D- signals to GPIOs {IDF_TARGET_USB_DP_GPIO_NUM} and {IDF_TARGET_USB_DM_GPIO_NUM} respectively. For USB device functionality, these GPIOs should be connected to the bus in some way (e.g., via a Micro-B port, USB-C port, or directly to standard-A plug).
The Device Stack is distributed via the `ESP Component Registry <https://components.espressif.com/components/espressif/esp_tinyusb>`__. Thus, to use it, please add the Device Stack component as dependency using the following command:
When Device Stack supports high-speed, both :cpp:member:`fs_configuration_descriptor` and :cpp:member:`hs_configuration_descriptor` should be present to comply with USB 2.0 specification.
The Device Stack will instantiate a USB device based on the descriptors provided in the fields described above when :cpp:func:`tinyusb_driver_install` is called.
The Device Stack also provides default descriptors that can be installed by setting the corresponding field in :cpp:func:`tinyusb_driver_install` to ``NULL``. Default descriptors include:
- Default device descriptor: Enabled by setting :cpp:member:`device_descriptor` to ``NULL``. Default device descriptor will use the values set by the corresponding menuconfig options (e.g., PID, VID, bcdDevice etc).
- Default string descriptor: Enabled by setting :cpp:member:`string_descriptor` to ``NULL``. Default string descriptors will use the value set by corresponding menuconfig options (e.g., manufacturer, product, and serial string descriptor options).
- Default configuration descriptor. Some classes that rarely require custom configuration (such as CDC and MSC) will provide default configuration descriptors. These can be enabled by setting associated configuration descriptor field to ``NULL``:
For backward compatibility, when Device Stack supports high-speed, the field :cpp:member:`configuration_descriptor` could be used instead of :cpp:member:`fs_configuration_descriptor` for full-speed configuration descriptor.
To install the Device Stack, please call :cpp:func:`tinyusb_driver_install`. The Device Stack's configuration is specified in a :cpp:type:`tinyusb_config_t` structure that is passed as an argument to :cpp:func:`tinyusb_driver_install`.
The :cpp:type:`tinyusb_config_t` structure can be zero-initialized (e.g., ``const tinyusb_config_t tusb_cfg = { 0 };``) or partially (as shown below). For any member that is initialized to ``0`` or ``NULL``, the stack uses its default configuration values for that member, see example below.
USB specification mandates self-powered devices to monitor voltage levels on USB's VBUS signal. As opposed to bus-powered devices, a self-powered device can be fully functional even without a 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 4.75 V and invalid if it falls below 4.35 V.
On the {IDF_TARGET_NAME}, this will require using a GPIO to act as a voltage sensing pin to detect when VBUS goes above/below the prescribed thresholds. However, {IDF_TARGET_NAME} pins are 3.3 V tolerant. Thus, even if VBUS rises/falls above/below the thresholds mentioned above, it would still appear as a logic HIGH to the {IDF_TARGET_NAME}. Thus, in order to detect the VBUS valid condition, users can do one of the following:
- Connect VBUS to a voltage comparator chip/circuit that detects the thresholds described above (i.e., 4.35 V and 4.75 V), and outputs a 3.3 V logic level to the {IDF_TARGET_NAME} indicating whether VBUS is valid or not.
- Use a resistor voltage divider that outputs (0.75 x Vdd) if VBUS is 4.4 V (see figure below).
..note::
In either case, the voltage on the sensing pin must be logic low within 3 ms after the device is unplugged from the USB host.
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 is used for VBUS monitoring.
If the CDC option is enabled in Menuconfig, the USB Serial Device can be initialized with :cpp:func:`tusb_cdc_acm_init` according to the settings from :cpp:type:`tinyusb_config_cdcacm_t`, see example below.
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.
The USB Serial Device allows the redirection of all standard input/output streams (stdin, stdout, stderr) to USB. Thus, calling standard library input/output functions such as ``printf()`` will result into the data being sent/received over USB instead of UART.
Users should call :cpp:func:`esp_tusb_init_console` to switch the standard input/output streams to USB, and :cpp:func:`esp_tusb_deinit_console` to switch them back to UART.
If the MSC ``CONFIG_TINYUSB_MSC_ENABLED`` option is enabled in Menuconfig, the ESP Chip can be used as USB MSC Device. The storage media (SPI-Flash or SD-Card) can be initialized as shown below.
