USB-C Port on Voxl 2 Mini

[bendraper]

If I were to use a USB C breakout board to connect to a USB A ethernet adapter (just a pdb for consolidating space), will the Voxl require a CC resistor on the USB for negotiation? Or could I just use something like this https://www.digikey.com/en/products/detail/adafruit-industries-llc/5180/15287551?utm_adgroup=&utm_source=google&utm_medium=cpc&utm_campaign=PMax Shopping_Product_High ROAS Categories&utm_term=&utm_content=&gclid=Cj0KCQjwtJKqBhCaARIsAN_yS_lTlKOorgebACjn6JgJ4PSgA-ffYGH5xnw3K0EXZeDwTNLaVlZdyCAaAoz2EALw_wcB

[Vinny]

Hi @bendraper
This is a good question with a lot of little nuances.
To be honest, I am not 100% sure (yet). We just normally use a USB-C to (whatever) adapter we need, and typically, with USB-C being very smart, it figures it out.
Like this: https://www.l-com.com/usb-usb-adapter-type-c-male-to-type-a-female

Unlike UBS2 with the ID pin, the roles in USB-C are done over packet exchanges.
I'm pretty sure the first aspect of this is VBUS and if there are pull-downs or pull-ups on the D+/D- lines, basically "legacy mode".
So, if you just pick up USB D+/D-, VBUS, and DGND, and connect it to a peripheral that does not have a VBUS, and has the legacy D+/D- signaling, I think the Qualcomm chipset will figure that out and enumerate as host. We have not tried our own custom adapter to see if there are any other subtleties here.
It might be worth breaking open one of those adapters I posted above to see what they do.

Give it a shot and keep us posted. I'll do some of my own research here to be sure, and if I need to I'll reach out to Qualcomm.

Thanks!

[Vinny]

@bendraper
I did just submit a ticket with Qualcomm since I cannot find any tips in their docs for this use case.
I have to imagine other folks using these chips want just a USB2 OTG connector??? Maybe it is not supported? Not sure...

I'll let you know what I find out.

[Vinny]

Hi @bendraper
Doing a little more research on this, Microchip has a good app note effectively confirming what you originally asked...
https://ww1.microchip.com/downloads/en/Appnotes/00001914B.pdf
(if the link doesn't work, just search for AN1914)
I'd give it a shot... seems easy to try...
You would need to provide the CC resistors as RPD (5.1K) to GND to enable the Voxl2 Mini USBC port to enumerate with you as a peripheral in USB2. I would not be surprised to find just those 2 R's in the ubiquitous USBC to USB-A adapters.
Keep me posted.
Thanks!

[Vinny]

Hi @bendraper
Sorry for all the spam, but we did get confirmation from a Qualcomm Applications Engineer confirming all of this.
Basically, the interaction between the on-board PMICs and the QRB5165 follows USB spec as follows for Legacy Mode:

• Float all USB SS signals
• VBUS and DGND as expected
• Use HS signals as expected
• CC1 functions as "ID" in USB2 OTG Legacy (not CC2, can be floated), so provide the Rpd resistor to GND to indicate HOST MODE (you are plugging in a peripheral)

So, if you want to plug-into our USB-C, you need to short CC1/CC2 to account for reverse insertion, or unless that little breakout board you have already does that and presents to you one CC signal, you can treat that one CC signal as "ID".

That really should be it... Let me know how it goes.
Thanks!

[bendraper]

@Vinny Thanks Vinny for looking into this! I'm going to do some bench tests knowing this and will let you know how it goes!