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Re: problems with USB/CDC serial (umodem) - devices work with Linux, Mac OS X, and FreeBSD, but not NetBSD (Martin Husemann) writes:

>On Mon, Feb 18, 2019 at 09:11:51AM -0800, Rob Newberry wrote:
>> I'm pretty sure there are differences in how NetBSD's USB modem class
>> driver interacts with the device from how other platforms do.  For the
>> time being, I'm trying to read the code of the NetBSD and the FreeBSD
>> drivers, along with the USB CDC spec, to see what's going on.

>Hmm, I thought I would be using umodem, but actually it is u3g.
>However, I am pretty sure that at that level the driver does not
>do anything special but just pass on the data in both ways.

I'm using umodem for a 3G interface, nothing special there.

You also see from the traces that the same data is sent and the
first byte received is also the same. This could be as simple
as a timeout on NetBSD, I first thought something was using very
small timeouts that cannot be handled with our low HZ value, but
the code seems to use only timeouts of at least several seconds.

The code also uses a rare combination of select() and poll() to
wait for input. I tend to believe the problem is not related to
USB or umodem at all.

                                Michael van Elst
                                "A potential Snark may lurk in every tree."

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