USB-1: Dealing with USB Events

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.

✅ Open the firmware/src/bin/ file.

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.

✅ Connect the USB cable to the port J3 then run the starter code.

❗️ Keep the cable connected to the J3 port for the rest of the workshop

This code will panic because USBRESET is not implemented yet.

✅ Go to fn on_event, line 39. In this section you'll need to implement the following USB events USBRESET and EP0SETUP so that your log output will look like this:

USBD initialized
USB: UsbReset
returning to the Default state
USB: UsbEp0Setup
goal reached; move to the next section


  • 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 adding a log statement to provide information that this event occurred.

  • EP0DATADONE. The USBD peripheral is signaling the end of the DATA stage of a control transfer. Since you won't encounter this event just yet, you can leave it as it is.

  • EP0SETUP. The USBD peripheral has detected the SETUP stage of a control transfer. Add a log statement containing "goal reached; move to the next section" and exit the application.

You can find the solution in the file.