2.7 KiB
Next Steps
String descriptors
If you'd like to continue working on your workshop project, we recommend adding String Descriptors support to the USB firmware. To do this, follow these steps:
✅ Read through section 9.6.7 of the USB spec, which covers string descriptors.
✅ Change your configuration descriptor to use string descriptors. You'll want to change the iConfiguration field to a non-zero value. Note that this change will likely break enumeration.
✅ Re-run the program to see what new control requests you get from the host.
✅ Update the usb parser to handle the new requests.
✅ 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.
✅ If this works, add 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, 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.
Explore more RTIC features
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. We encourage you to check out that implementation, test it on different OSes and report issues, or contribute fixes, to the usb-device ecosystem.