USB stack

[japaric]

This issue is for gathering resources on writing USB firmware in Rust and for tracking progress on building a generic USB stack in Rust.

This is basically a place where people working on USB firmware can post about the progress they have made, exchange notes, etc.

People that have been doing USB stuff (that I know of):

• @jgouly has ported some C firmware that incorporates USB functionality for a NXP microcontroller to Rust.
• @kinnison has been blogging about writing a USB stack in Rust using a STM32 microcontroller as the development platform. Though they seem to taking a well deserved break at the time of opening this issue. Thank you for all your blog posts! ❤️
• Tock has a USB 2.0 capsule. I can't tell if has functionality beyond enumeration though (cc @alevy). User facing interface | Kernel Hardware Interface Layer (HIL) | HIL implementation for the SAM4L.
• @nallar has "been trying to get USB working here on the blue pill".

[alevy]

@japaric RE: Tock, it can enumerate as well as send/receive data via control endpoints. Bulk and interrupt endpoints isn't much different but hasn't been implemented yet. Also looking at implementing the interfaces for the new NRF52 (which has USB stack) and a Synergy-IP-base one (which I believe is the same as the STM32 series). Those span very different levels of abstraction from the hardware, which we're hoping will help either validate or suggest changes to the interface.

Related note, I think the really hard part, in general, for this is going to be abstracting enumeration since lots of hardware seems to want the descriptors to be laid out in particular ways in memory that are often quite different. So my 2 cents is that's gonna be the interesting place to focus on interface (Tock hasn't really done that yet, aside from taking a guess)

[jcsoo]

I've been working on USB stacks for a couple of different MCUs (STM32F4 / F7 and K64, hoping to get to STM32F0, STM32L4 and SAMD21 soon) and device classes (HID, CDC-ACM, CDC-EEM, and hopefully CDC-ECM soon). I feel like I have a reasonable grasp of potential traits for basic lower-level USB drivers that could work across all of these - you set up descriptors and buffers owned by the driver and simply copy into them. I think it should also be possible to come up with lower level traits to support zero-copy buffer passing, but implementation would be quite a bit more complicated and I don't currently have any boards with USB HS that would justify the effort.

I haven't run across any issues in sending descriptors themselves - as far as I know, they are just data. There may be some issues in constructing the descriptors themselves. I've mostly pre-generated device descriptors as const data and then copied them onto the stack, updating fields as necessary before sending them.

It would be really nice to have a Rust crate to construct and parse descriptors, particularly HID reports descriptors.

[LunNova]

I've been trying to get USB working here on the blue pill: https://github.com/nallar/BluePillKeyboard/blob/master/src/usb/mod.rs

Doesn't work yet and uses types from stm32f103xx so couldn't be used with anything else.

[kinnison]

I got very stuck when trying to work out how to update svd2rust to deal with registers which contained write-to-toggle bits (the stm32f103 and similar devices have, in their USB peripherals, registers which contain read/write bits where you write zero to leave alone and 1 to toggle).

[japaric]

@kinnison Could you open an issue in the svd2rust repo describing the issue you are running into? I'd be happy to look into it.

@nallar

uses types from stm32f103xx so couldn't be used with anything else.

I think that's fine to start with. We should have at least, ideally independent, two implementations of USB for different devices then we can think about what, or what level, things can / should be abstracted into traits / common types.

[lylecheatham]

I'm interested in potentially using rust to write firmware for a 3D printer, but it would most definitely require a USB stack as the bandwidth difference between using real USB vs something like an FTDI is several orders of magnitude.

[wez]

I'm interested in contributing time on this for the ATSAMD21 boards that adafruit produces (#61)

[ah-]

I've now got simple USB with enumeration and HID input working on an STM32L1: https://github.com/ah-/anne-key/tree/master/src/usb

It's still pretty rough, but it works. Will clean it up over the next few days.

[zklapow]

@wez have you made any progress on your USB work for the SAMD21? I am also starting to work on a USB stack for the SAMD21G18A but I know next to nothing about USB so it has been slow going so far

[wez]

@zklapow https://github.com/wez/atsamd21-rs/tree/master/hal/src/usb is where I've started to pull some things together. It's a very thin veneer over the peripherals at this stage. I've also been studying a couple of other implementations (tock and the anne-key mentioned above) and reading specs.

[zklapow]

@wez awesome I saw that and have been building off it a bit, you may see some PRs from me soon!