.. currentmodule:: machine .. _machine.USBDevice: class USBDevice -- USB Device driver ==================================== .. note:: ``machine.USBDevice`` is currently only supported on the rp2 and samd ports. USBDevice provides a low-level Python API for implementing USB device functions using Python code. .. warning:: This low-level API assumes familiarity with the USB standard. There are high-level `usb driver modules in micropython-lib`_ which provide a simpler interface and more built-in functionality. Terminology ----------- - A "Runtime" USB device interface or driver is one which is defined using this Python API after MicroPython initially starts up. - A "Built-in" USB device interface or driver is one that is compiled into the MicroPython firmware, and is always available. Examples are USB-CDC (serial port) which is usually enabled by default. Built-in USB-MSC (Mass Storage) is an option on some ports. Lifecycle --------- Managing a runtime USB interface can be tricky, especially if you are communicating with MicroPython over a built-in USB-CDC serial port that's part of the same USB device. - A MicroPython soft reset will always clear all runtime USB interfaces, which results in the entire USB device disconnecting from the host. If MicroPython is also providing a built-in USB-CDC serial port then this will re-appear after the soft reset. This means some functions (like ``mpremote run``) that target the USB-CDC serial port will immediately fail if a runtime USB interface is active, because the port goes away when ``mpremote`` triggers a soft reset. The operation should succeed on the second try, as after the soft reset there is no more runtime USB interface. - To configure a runtime USB device on every boot, it's recommended to place the configuration code in the ``boot.py`` file on the :ref:`device VFS `. On each reset this file is executed before the USB subsystem is initialised (and before ``main.py``), so it allows the board to come up with the runtime USB device immediately. - For development or debugging, it may be convenient to connect a hardware serial REPL and disable the built-in USB-CDC serial port entirely. Not all ports support this (currently only ``rp2``). The custom build should be configured with ``#define MICROPY_HW_USB_CDC (0)`` and ``#define MICROPY_HW_ENABLE_UART_REPL (1)``. Constructors ------------ .. class:: USBDevice() Construct a USBDevice object. .. note:: This object is a singleton, each call to this constructor returns the same object reference. Methods ------- .. method:: USBDevice.config(desc_dev, desc_cfg, desc_strs=None, open_itf_cb=None, reset_cb=None, control_xfer_cb=None, xfer_cb=None) Configures the ``USBDevice`` singleton object with the USB runtime device state and callback functions: - ``desc_dev`` - A bytes-like object containing the new USB device descriptor. - ``desc_cfg`` - A bytes-like object containing the new USB configuration descriptor. - ``desc_strs`` - Optional object holding strings or bytes objects containing USB string descriptor values. Can be a list, a dict, or any object which supports subscript indexing with integer keys (USB string descriptor index). Strings are an optional USB feature, and this parameter can be unset (default) if no strings are referenced in the device and configuration descriptors, or if only built-in strings should be used. Apart from index 0, all the string values should be plain ASCII. Index 0 is the special "languages" USB descriptor, represented as a bytes object with a custom format defined in the USB standard. ``None`` can be returned at index 0 in order to use a default "English" language descriptor. To fall back to providing a built-in string value for a given index, a subscript lookup can return ``None``, raise ``KeyError``, or raise ``IndexError``. - ``open_itf_cb`` - This callback is called once for each interface or Interface Association Descriptor in response to a Set Configuration request from the USB Host (the final stage before the USB device is available to the host). The callback takes a single argument, which is a memoryview of the interface or IAD descriptor that the host is accepting (including all associated descriptors). It is a view into the same ``desc_cfg`` object that was provided as a separate argument to this function. The memoryview is only valid until the callback function returns. - ``reset_cb`` - This callback is called when the USB host performs a bus reset. The callback takes no arguments. Any in-progress transfers will never complete. The USB host will most likely proceed to re-enumerate the USB device by calling the descriptor callbacks and then ``open_itf_cb()``. - ``control_xfer_cb`` - This callback is called one or more times for each USB control transfer (device Endpoint 0). It takes two arguments. The first argument is the control transfer stage. It is one of: - ``1`` for SETUP stage. - ``2`` for DATA stage. - ``3`` for ACK stage. Second argument is a memoryview to read the USB control request data for this stage. The memoryview is only valid until the callback function returns. Data in this memoryview will be the same across each of the three stages of a single transfer. A successful transfer consists of this callback being called in sequence for the three stages. Generally speaking, if a device wants to do something in response to a control request then it's best to wait until the ACK stage to confirm the host controller completed the transfer as expected. The callback should return one of the following values: - ``False`` to stall the endpoint and reject the transfer. It won't proceed to any remaining stages. - ``True`` to continue the transfer to the next stage. - A buffer object can be returned at the SETUP stage when the transfer will send or receive additional data. Typically this is the case when the ``wLength`` field in the request has a non-zero value. This should be a writable buffer for an ``OUT`` direction transfer, or a readable buffer with data for an ``IN`` direction transfer. - ``xfer_cb`` - This callback is called whenever a non-control transfer submitted by calling :func:`USBDevice.submit_xfer` completes. The callback has three arguments: 1. The Endpoint number for the completed transfer. 2. Result value: ``True`` if the transfer succeeded, ``False`` otherwise. 3. Number of bytes successfully transferred. In the case of a "short" transfer, The result is ``True`` and ``xferred_bytes`` will be smaller than the length of the buffer submitted for the transfer. .. note:: If a bus reset occurs (see :func:`USBDevice.reset`), ``xfer_cb`` is not called for any transfers that have not already completed. .. method:: USBDevice.active(self, [value] /) Returns the current active state of this runtime USB device as a boolean. The runtime USB device is "active" when it is available to interact with the host, it doesn't mean that a USB Host is actually present. If the optional ``value`` argument is set to a truthy value, then the USB device will be activated. If the optional ``value`` argument is set to a falsey value, then the USB device is deactivated. While the USB device is deactivated, it will not be detected by the USB Host. To simulate a disconnect and a reconnect of the USB device, call ``active(False)`` followed by ``active(True)``. This may be necessary if the runtime device configuration has changed, so that the host sees the new device. .. attribute:: USBDevice.builtin_driver This attribute holds the current built-in driver configuration, and must be set to one of the ``USBDevice.BUILTIN_`` named constants defined on this object. By default it holds the value :data:`USBDevice.BUILTIN_NONE`. Runtime USB device must be inactive when setting this field. Call the :func:`USBDevice.active` function to deactivate before setting if necessary (and again to activate after setting). If this value is set to any value other than :data:`USBDevice.BUILTIN_NONE` then the following restrictions apply to the :func:`USBDevice.config` arguments: - ``desc_cfg`` should begin with the built-in USB interface descriptor data accessible via :data:`USBDevice.builtin_driver` attribute ``desc_cfg``. Descriptors appended after the built-in configuration descriptors should use interface, string and endpoint numbers starting from the max built-in values defined in :data:`USBDevice.builtin_driver` attributes ``itf_max``, ``str_max`` and ``ep_max``. - The ``bNumInterfaces`` field in the built-in configuration descriptor will also need to be updated if any new interfaces are appended to the end of ``desc_cfg``. - ``desc_strs`` should either be ``None`` or a list/dictionary where index values less than ``USBDevice.builtin_driver.str_max`` are missing or have value ``None``. This reserves those string indexes for the built-in drivers. Placing a different string at any of these indexes overrides that string in the built-in driver. .. method:: USBDevice.submit_xfer(self, ep, buffer /) Submit a USB transfer on endpoint number ``ep``. ``buffer`` must be an object implementing the buffer interface, with read access for ``IN`` endpoints and write access for ``OUT`` endpoints. .. note:: ``ep`` cannot be the control Endpoint number 0. Control transfers are built up through successive executions of ``control_xfer_cb``, see above. Returns ``True`` if successful, ``False`` if the transfer could not be queued (as USB device is not configured by host, or because another transfer is queued on this endpoint.) When the USB host completes the transfer, the ``xfer_cb`` callback is called (see above). Raises ``OSError`` with reason ``MP_EINVAL`` If the USB device is not active. .. method:: USBDevice.stall(self, ep, [stall] /) Calling this function gets or sets the STALL state of a device endpoint. ``ep`` is the number of the endpoint. If the optional ``stall`` parameter is set, this is a boolean flag for the STALL state. The return value is the current stall state of the endpoint (before any change made by this function). An endpoint that is set to STALL may remain stalled until this function is called again, or STALL may be cleared automatically by the USB host. Raises ``OSError`` with reason ``MP_EINVAL`` If the USB device is not active. Constants --------- .. data:: USBDevice.BUILTIN_NONE .. data:: USBDevice.BUILTIN_DEFAULT .. data:: USBDevice.BUILTIN_CDC .. data:: USBDevice.BUILTIN_MSC .. data:: USBDevice.BUILTIN_CDC_MSC These constant objects hold the built-in descriptor data which is compiled into the MicroPython firmware. ``USBDevice.BUILTIN_NONE`` and ``USBDevice.BUILTIN_DEFAULT`` are always present. Additional objects may be present depending on the firmware build configuration and the actual built-in drivers. .. note:: Currently at most one of ``USBDevice.BUILTIN_CDC``, ``USBDevice.BUILTIN_MSC`` and ``USBDevice.BUILTIN_CDC_MSC`` is defined and will be the same object as ``USBDevice.BUILTIN_DEFAULT``. These constants are defined to allow run-time detection of the built-in driver (if any). Support for selecting one of multiple built-in driver configurations may be added in the future. These values are assigned to :data:`USBDevice.builtin_driver` to get/set the built-in configuration. Each object contains the following read-only fields: - ``itf_max`` - One more than the highest bInterfaceNumber value used in the built-in configuration descriptor. - ``ep_max`` - One more than the highest bEndpointAddress value used in the built-in configuration descriptor. Does not include any ``IN`` flag bit (0x80). - ``str_max`` - One more than the highest string descriptor index value used by any built-in descriptor. - ``desc_dev`` - ``bytes`` object containing the built-in USB device descriptor. - ``desc_cfg`` - ``bytes`` object containing the complete built-in USB configuration descriptor. .. _usb driver modules in micropython-lib: https://github.com/micropython/micropython-lib/tree/master/micropython/usb#readme