The USBD peripheral on the nRF52840 contains a series of registers, called EVENTS registers, that indicate the reason for entering the USBD event handler. These events must be handled by the application to complete the enumeration process.
In this starter code the USBD peripheral is initialized in `init` and a task, named `main`, is bound to the interrupt signal USBD. This task will be called every time a new USBD event needs to be handled. The `main` task uses `usbd::next_event()` to check all the event registers; if any event is set (occurred) then the function returns the event, represented by the `Event` enum, wrapped in the `Some` variant. This `Event` is then passed to the `on_event` function for further processing.
-`USBRESET`. This event indicates that the host issued a USB reset signal. According to the USB specification this will move the device from any state to the `Default` state. Since we are currently not dealing with any other state, you can handle this state by doing nothing.
-`EP0SETUP`. The USBD peripheral has detected the SETUP stage of a control transfer. If you get to this point move to the next section.
-`EP0DATADONE`. The USBD peripheral is signaling the end of the DATA stage of a control transfer. You won't encounter this event just yet.
When you are done you should see this output:
``` console
(..)
INFO:usb_1 -- USB: UsbEp0Setup
INFO:usb_1 -- goal reached; move to the next section
```
Do not overthink this exercise; it is not a trick question. There is very little to do and no new functionality to add.
You can find the solution in the `usb-1-solution.rs` file.
