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29 lines
1.9 KiB
Markdown
29 lines
1.9 KiB
Markdown
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# USB-1: Dealing with USB Events
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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.
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Open the `firmware/src/bin/usb-1.rs` 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.
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Connect the USB cable to the port J3 then run the starter code.
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In this section as a warm-up exercise you'll need to deal with the following USB events until you reach the EP0SETUP event.
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- `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.
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- `EP0SETUP`. The USBD peripheral has detected the SETUP stage of a control transfer. If you get to this point move to the next section.
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- `EP0DATADONE`. The USBD peripheral is signaling the end of the DATA stage of a control transfer. You won't encounter this event just yet.
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When you are done you should see this output:
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``` console
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(..)
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INFO:usb_1 -- USB: UsbEp0Setup
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INFO:usb_1 -- goal reached; move to the next section
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```
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Do not overthink this exercise; it is not a trick question. There is very little to do and no new functionality to add.
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You can find the solution in the `usb-1-solution.rs` file.
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Before we continue we need to discuss how data transfers work under the USB protocol.
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