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embedded-trainings-2020/embedded-workshop-book/src/advanced-next-steps.md
Jorge Aparicio 57f373d7a8 remove empty sections; add open-ended exercises 
participants can try these after the workshop e.g. during the impl days
2020-07-13 19:18:52 +02:00

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Next Steps

String descriptors

Here's one more USB exercise for you: add string descriptors support to the USB firmware.

  • First, you'll want to read through section 9.6.7 of the USB spec, which covers string descriptors.
  • Next, we suggest you change your configuration descriptor to use string descriptors. You'll want to change the iConfiguration field to a non-zero value.
  • Now, re-run the program to see what new control requests you get from the host.
  • You'll need to update the usb parser to handle the new requests.
  • Then you can extend the logic of ep0setup to handle these new requests.
  • Eventually, you'll need to send a string descriptor to the host. Note here that Rust string literals are UTF-8 encoded but the USB protocol uses UTF-16 strings. You'll need to convert between these formats.
  • After you have iConfiguration working you can start adding strings to other descriptors like the device descriptor e.g. its iProduct field.

To verify that string descriptors are working in a cross-platform way you can extend the print-descs program to also print the device's string descriptors. See the read_string_descriptor method but note that this must be called on a "device handle", which is what the commented out open operation does.

RTIC

We have covered only a few of the core features of the RTIC framework but the framework has many more features like software tasks, tasks that can be spawned by the software; message passing between tasks; and task scheduling, which allows the creation of periodic tasks. We encourage to check the RTIC book which describes the features we haven't covered here.

usb-device

usb-device is a library for building USB devices. It has been built using traits (the pillar of Rust's generics) such that USB interfaces like HID and TTY ACM can be implemented in a device agnostic manner. The device details then are limited to a trait implementation. There's a work in progress implementation of the usb-device trait for the nRF52840 device in this PR and there are many usb-device "classes" like HID and TTY ACM that can be used with that trait implementation.