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USB-IF Releases I3C Device Class Specification

Published on Jul 17, 2022

I've been meaning to write about this for a while now, and regrettably it's already old news at this point. But it's actually a very important topic that's worthy of some additional time in the spotlight. The USB Implementers Forum (USB-IF) published the I3C Device Class Specification v1.0 back in January 2022. This only came to my attention when MIPI announced the release of this publication as a resulf of collaboration between the USB-IF and the MIPI I3C Working Group in mid-March, several months later. Their blog post covers a lot of interesting details as well as their motivation and goals and is certainly worth a read.

I think this is a really proactive move to get a custom device class defined in the early days of I3C adoption, as it will pave a clear path forward for USB to I3C Bridge implementations. With a standard already defined, the risk of ending up with multiple manufacturer-specific implementations is minimized and will result in a cohesive I3C ecosystem.

I had a chance to speak with an engineer knowledgeable on this effort while attending the I3C Interop Workshop last month and he mentioned there is forward momentum on getting device driver support for Windows, MacOS, and Linux, with the ultimate goal of getting it included as an official driver distributed with the OS. I think this is critical to the success of the device class adoption -- whereas the ease of use of a device class of a standard driver (such as HID) might be a more interesting approach to eliminate what could be a very painful battle with device driver support. I'm really interested in seeing how this plays out over the coming months.

Once the driver is readily available, the cherry on top of the I3C sundae we've all just been served will be for a manufacturer to provide an official example implemenation of this device class implemented in their USB stack / SDK. (I'm looking at you, NXP MCUXpresso team), or even better yet, in a popular open-source USB stack such as tinyusb.

Finally, I dropped in at FTDI's booth at Embedded World 2022 to see if they had I3C-capable USB bridge ICs on their roadmap -- I figured for a company who's bread-and-butter is in the USB Bridge IC space, they'd be eager to jump on this opportunity. However the folks I spoke with at their booth were not even aware of I3C, so if it's something even on their roadmap, it hasn't made it far enough along for their marketing team to even be aware of it yet. I also reached out to their customer support team separately to inquire about I3C support and was informed that they do not have anything planned yet.

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