[time-nuts] Sure Electronics GPS card, Linux quirk

Don Latham djl at montana.com
Sun Feb 5 05:24:06 UTC 2012

The CP2102 is featured in Chinese ebay 4 buck usb-232 adapters. The chip
suffers from serious bad-driveritis, and I've had to do 'net research to
make it useful with various flavors of Windoze.

Hal Murray
> I'm in the habit of using things like:
>   cat /dev/ttyUSB0
> when checking out GPS that I expect to send ASCII.
> When I tried that with my new toy, it went bonkers.  In particular, the
> firmware LED went on, and the NMEA LED switched from blinking to solid
> on.
> The data included the stuff I expected, but it also included a lot of
> garbage.
> I (finally) tracked that down to "echo" being set on the tty parameters.
> That echos a copy of each input character back to where it came from.
> The
> cure is as simple as:
>   stty -F /dev/ttyUSB0 -echo
> Of course, there are other ways to get in trouble with tty parameters.
> Here
> is the line I have stashed away in my notes on how to set things up:
>   stty -F /dev/ttyxxx 9600 igncr clocal -echo -ixon
> Now that I've got that sorted out, it responds to the $PTMKxxx commands.
> (I've only tried one.)
> The Sure card uses the ST CP2102 USB to serial chip.  It's not very
> common,
> but there is a Linux driver for it.  I assume the default bits somewhere
> in
> the driver are different from defaults in the FTDI FT23x and the
> Prolific
> PL230x chips that are quite common.  I haven't looked at the source
> code.
> In my quest for a low cost, no-soldering GPS gizmo that works well with
> NTP,
> I tried a Transystem GM-2.  It had the same sort of garbage.  That was a
> while ago.  I gave up and put it on the back burner.  Guess what.  It
> uses
> the same USB-serial chip.  It's working now.
> --
> These are my opinions, not necessarily my employer's.  I hate spam.
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"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
R. Bacon
"If you don't know what it is, don't poke it."
Ghost in the Shell

Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304

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