USB HUB problems

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kumpisteszta9
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USB HUB problems

Unread post by kumpisteszta9 » Mon May 13, 2019 11:43 pm

Hi there!

I'm working on a project which requires multiple serial connections so I picked up some CH341 chip based USB serial converters and connected them to the 4 USB ports on the side of the Odroid-C2.
I'm having latency issues, so basically sometimes there's around 800ms of delay before the serial converters get any data. I managed to narrow down the problem to the built in USB HUB of the C2.
So if I connect the serial converter to one of the 4 usb port there's latency, BUT if I connect an external USB HUB to the OTG port and plug the serial converter into that it works 100% of the time.

The C2 detects the serial converters without any problems and there are no "dmesg" issues even when the delays happen.

I used multiple applications to test the serial port (dotnet core v2.2 based, C++/open, wiringPI for C2, terminal apps) and the result is the same. The way I test is basically I just send characters, then stop for a second and start sending again, around half of the time there's a big delay before the serial port stars to send again. On the receiver side I used FTDI FT232 and CH341 chips connected to a Windows PC (I confirmed that the delay is not on the receiver side).

I read about an issue about the built in USB HUB which used to "hibernate", and I'm thinking this might be releated to that?

I'm running the Ubuntu-Mate V3.0 ("ubuntu-18.04-3.16-mate-odroid-c2-20180620.img.xz") image from the Odroid Wiki. I also tested the issue with a second Odroid-C2 with the same setup and I can replicate the issue.

I don't really know what to do about this issue, is there some power saving settings releated to the USB HUB, or some kind of newer driver?

Thanks.

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odroid
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Re: USB HUB problems

Unread post by odroid » Tue May 14, 2019 8:28 am

I think the MTT USB hub controller IC (GENESYS LOGIC GL852G)on the C2 seems to causes the random delay.
You can find the C2 schematics in this link. https://wiki.odroid.com/odroid-c2/hardware/hardware

Can you find which IC exists in your external USB hub?
Also check the CPU performance governor and IRQ assignment on your Ubuntu system to reduce the latency.

kumpisteszta9
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Re: USB HUB problems

Unread post by kumpisteszta9 » Tue May 14, 2019 7:07 pm

odroid wrote:
Tue May 14, 2019 8:28 am
I think the MTT USB hub controller IC (GENESYS LOGIC GL852G)on the C2 seems to causes the random delay.
You can find the C2 schematics in this link. https://wiki.odroid.com/odroid-c2/hardware/hardware

Can you find which IC exists in your external USB hub?
Also check the CPU performance governor and IRQ assignment on your Ubuntu system to reduce the latency.
Yes, it seems like the GL852G causes the problems.

The external USB HUB has a Terminus FE2.1 chip in it.

How do I check the IRQ assignments?

Thanks.

EDIT: The CPU governor is set to "performance" for all 4 cores.

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Re: USB HUB problems

Unread post by odroid » Wed May 15, 2019 8:39 am

IRQ assignment didn't help probably.
I could recall another user had a very similar issue with GL852G last night. :(
viewtopic.php?f=141&t=34245
Sorry about that.

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