Mailinglist Archive: opensuse (882 mails)

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Re: [opensuse] Serial to USB adaptor
  • From: Roger Oberholtzer <roger@xxxxxx>
  • Date: Fri, 03 Dec 2010 09:20:58 +0100
  • Message-id: <1291364458.6869.57.camel@xxxxxxxxxxxx>
On Fri, 2010-12-03 at 09:09 +0100, Per Jessen wrote:
Roger Oberholtzer wrote:

port. We have decided that the good old RS-232 is still best for this
type of thing. Too bad real ports are going away. I guess we will soon
be adding RS-232 interface cards to systems.

Moxa has some really neat serial-to-ethernet boxes.

I have seen such devices. The problem is the non-deterministic nature of
packets on the ethernet, versus the hardware interrupt caused by the
serial port line toggle done by the GPS.

The issue is that we are striving for centimeter accuracy with these
receivers (they are GPS with integrated inertial navigation systems that
solve locations using Kalman filtering). As a minimum, we need to know
the time we were at some location when the GPS/INS did some calculation.
The time when things happen is the core data used here. At 90 km/h, a
vehicle is moving 25 meters per second. So to even begin to entertain
thoughts of achieving this accuracy, the accuracy of the time tag for
the event should be better than 1/2500 of a second. Obtaining the PPS
over the serial port with this or better accuracy is no problem.
Obtaining the same over USB or ethernet is less provable.

But we are always looking. Serial ports are going the way of the dodo.
Even if there are some real world needs for them. Just not enough of
them to keep them standard on consumer grade computers.

--
Roger Oberholtzer

OPQ Systems / Ramböll RST

Ramböll Sverige AB
Krukmakargatan 21
P.O. Box 17009
SE-104 62 Stockholm, Sweden

Office: Int +46 10-615 60 20
Mobile: Int +46 70-815 1696

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