The USBD peripheral on the nRF52840 contains a series of registers, called EVENTS registers, that indicate the reason for entering the USBD interrupt handler. These events must be handled by the application to complete the enumeration process.
✅ Open the nrf52-code/usb-app/src/bin/usb-1.rs file.
In this starter code the USBD peripheral is initialized in init and a task, named handle_usb_interrupt, is bound to the interrupt signal called USBD. This task will be called every time a new USBD event needs to be handled. The handle_usb_interrupt task uses usbd::next_event() to check all the event registers; if any event is set (i.e. that event just 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 Event::UsbReset is not handled yet - it has a todo!() on the relevant match arm.
✅ Go to fn on_event(...), line 48. You'll need to handle the Event::UsbReset case - for now, just print the log message returning to the Default state.
✅ Now handle the Event::UsbEp0Setup case - for now, just print the log message usb-1 exercise complete and then execute dk::exit() to shut down the microcontroller.
Your logs should look like:
USBD initialized
USB: UsbReset
returning to the Default state
USB: UsbEp0Setup
usb-1 exercise completeYou can ignore the Event::UsbEp0DataDone event for now because we don't yet get far enough when talking to the host computer for this event to come up.
This event indicates that the host issued a USB reset signal - the first step in the enumeration process. 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, for now we just log that we received this event and move on.
The USBD peripheral has detected the SETUP stage of a control transfer. For now, we just print a log message and exit the application.
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.
You can find the solution in the nrf52-code/usb-app-solutions/src/bin/usb-1.rs file.