[LinuxPPS] LinuxPPS through USB interface

[Bernhard Schiffner]

On Thursday 19 March 2009 04:38:10 emorgen at comcast.net wrote:
> I read about a year's worth of questions on the forum and I could not find
> an exact match to my question so I apologise if my question has been
> answered.
>
> I have a GPS Eval chip from sparkfun and I wired a connection between the
> PPS port to the DCD port of the USB connection. Basically this card has two
> ports, serial and USB. The USB port is a serial converter port. When I try
> and run ppstest with a pps instance of the usb drive I get the following
> error:
>
> time_pps_fetch() error -1 (Connection timed out)
>
> If I connect the device through a normal serial port I get no issues with
> PPS. I have tested the connection with a scope and the data is being
> properly sent along the line. I'm wondering if LinuxPPS does not support
> USB serial emulation or if there is some setting I need.
>
> Please let me know if anyone has any tweaks or alternative methods to
> retrieve when the PPS signal arrives. I don't think LinuxPPS supports other
> pins so if I send the signal to a different port i'd have to modify the
> code to read from that port.
>
> Thank you in advance for any help you provide me. It is greatly
> appreciated.
>
> Sincerely,
>
> Eric Morgenstern

Hi Eric,

only a little hint. PSS is intended to gather very precise timing 
informations.
Best practice is the use of a suited (non intel) architekture and a special, 
single, interupt enabled (GPIO-) line.

The use of the serial / parallel port is "left over" from history, serves 
mostly as a POC / last ressort and causes its own sort of problems.

USB adds an other level of error because it is an bus with (possibly) a lot of 
participants. A USB - serial converter needs it's own patch to be useable 
with LinuxPPS. And nobody really wants (did) this until now...

Bernhard