Re: non-standard baud rates with Prolific 2303 USB-serial

[Johan Hovold <johan@kernel.org>]

On Tue, Feb 23, 2021 at 02:15:06PM -0500, Michael G. Katzmann wrote:
> On 2/23/21 11:52 AM, Johan Hovold wrote:
> > On Tue, Feb 23, 2021 at 11:30:41AM -0500, Michael G. Katzmann wrote:
> >> On 2/23/21 11:14 AM, Johan Hovold wrote:
> >>> I only have an HXD (and a GC) here.
> >>>
> >>> The HXD has bcdUSB as 1.10 unlike your TA with 2.00, but not sure that
> >>> helps.
> >> Sound promising .. why do you think this is this not reliable?
> > Perhaps it is. Perhaps even bcdDevice of 3.00 is enough (includes some
> > older variants that the TA replaced supposedly). Not sure anyone ever
> > tried the current scheme on those older models.
> >
> > Charles, could you post the output of "lsusb -v" for your PL2303TA? And
> > did you verify that you actually got 110 Bd with the current Linux
> > driver?
> >
> > Johan
> 
> Here is the USB packet capture from Wireshark oon Windows 10 when:
> 
> 1) plugging in pl2303 (packets 18-393)
> 
> 2) setting the device wia cmd line to 110/even/7 bits/2 stop (packets 393-690)
> 
> (device is on port 1.7)
> 
> https://drive.google.com/file/d/17TkV9JB2iFNdr4LvRftBnV3_DgITGvUH/view?usp=sharing
> 
> There are orders of magnitude more traffic than in Linux!

Thanks, I'm sure this will come in handy, but I haven't had time to dig
into it myself yet.

Best case, all TAs need the alternate encoding, but Charles seems to
suggest it isn't that easy and in which case the answer probably lies in
these traces.

Perhaps you can even figure out how to poll for an empty TX FIFO from
it, unless Charles is able to provide some details on that separate
matter?

Johan