doc: Using doxygen comments from the code for USB Core

Instead of documenting in rst, pull the API from USB Device Core Layer
header.

Fixes: #5702

Signed-off-by: Andrei Emeltchenko <[email protected]>

Author: finikorg

doc/subsystems/usb/usb.rst

@@ -55,124 +55,10 @@ functionalities:
    * Uses the APIs provided by the device controller drivers to interact with
      the USB device controller.
 
-Structures
-==========
-
-.. code-block:: c
-
-   typedef void (*usb_status_callback)(enum usb_dc_status_code status_code);
-
-Callback function signature for the device status.
-
-.. code-block:: c
-
-   typedef void (*usb_ep_callback)(u8_t ep,
-      enum usb_dc_ep_cb_status_code cb_status);
-
-Callback function signature for the USB Endpoint.
-
-.. code-block:: c
-
-   typedef int (*usb_request_handler) (struct usb_setup_packet *setup,
-      int *transfer_len, u8_t **payload_data);
-
-Callback function signature for class specific requests. For host to device
-direction the 'len' and 'payload_data' contain the length of the received data
-and the pointer to the received data respectively. For device to host class
-requests, 'len' and 'payload_data' should be set by the callback function
-with the length and the address of the data to be transmitted buffer
-respectively.
-
-.. code-block:: c
-
-   struct usb_ep_cfg_data {
-      usb_ep_callback ep_cb;
-      u8_t ep_addr;
-   };
-
-This structure contains configuration for a certain endpoint.
-   * ep_cb: callback function for notification of data received and available
-     to application or transmit done, NULL if callback not required by
-     application code.
-   * ep_addr: endpoint address. The number associated with the EP in the device
-     configuration structure.
-
-.. code-block:: c
-
-   struct usb_interface_cfg_data {
-      usb_request_handler class_handler;
-      usb_request_handler custom_handler;
-      u8_t *payload_data;
-   };
-
-This structure contains USB interface configuration.
-   * class_handler: handler for USB Class specific Control (EP 0)
-     communications.
-   * custom_handler: the custom request handler gets a first
-     chance at handling the request before it is handed over to the
-     'chapter 9' request handler.
-   * payload_data: this data area, allocated by the application, is used to
-     store class specific command data and must be large enough to store the
-     largest payload associated with the largest supported Class' command set.
-
-.. code-block:: c
-
-   struct usb_cfg_data {
-      const u8_t *usb_device_description;
-      usb_status_callback cb_usb_status;
-      struct usb_interface_cfg_data interface;
-      u8_t num_endpoints;
-      struct usb_ep_cfg_data *endpoint;
-   };
-
-This structure contains USB device configuration.
-   * usb_device_description: USB device description, see
-     http://www.beyondlogic.org/usbnutshell/usb5.shtml#DeviceDescriptors
-   * cb_usb_status: callback to be notified on USB connection status change
-   * interface:  USB class handlers and storage space.
-   * num_endpoints: number of individual endpoints in the device configuration
-   * endpoint: pointer to an array of endpoint configuration structures
-     (usb_cfg_data) of length equal to the number of EP associated with the
-     device description, not including control endpoints.
-
-The class drivers instantiates this with given parameters using the
-"usb_set_config" function.
-
-APIs
-====
-
-:c:func:`usb_set_config()`
-   This function configures USB device.
-
-:c:func:`usb_deconfig()`
-   This function returns the USB device back to it's initial state
-
-:c:func:`usb_enable()`
-   This function enable USB for host/device connection. Upon success, the USB
-   module is no longer clock gated in hardware, it is now capable of
-   transmitting and receiving on the USB bus and of generating interrupts.
-
-:c:func:`usb_disable()`
-   This function disables the USB device. Upon success, the USB module clock
-   is gated in hardware and it is no longer capable of generating interrupts.
-
-:c:func:`usb_write()`
-   write data to the specified endpoint. The supplied usb_ep_callback will be
-   called when transmission is done.
-
-:c:func:`usb_read()`
-   This function is called by the endpoint handler function after an OUT
-   interrupt has been received for that EP. The application must only call
-   this function through the supplied usb_ep_callback function.
-
-:c:func:`usb_transfer()`
-   This asynchronous function starts a usb transfer from/to a specified buffer.
-   A callback can be provided and will be called on transfer completion.
-   This function can be used in IRQ context.
-
-:c:func:`usb_transfer_sync()`
-   This function is the synchronous version of the usb_transfer function,
-   waiting for transfer completion before returning.
+USB Device Core Layer API
+=========================
+.. doxygengroup:: _usb_device_core_api
+   :project: Zephyr
 
 USB device class drivers
 ************************