Re: Serial port monitor

From: Paul Keinanen (keinanen_at_sci.fi)
Date: 05/06/04 

Date: Thu, 06 May 2004 23:54:40 +0300

On Thu, 06 May 2004 14:37:42 GMT, Bryan Hackney
<bh.remove@bhconsult.com> wrote:

>Make a dual-snooper cable. You need two ports on your working computer.
>Tee off TX-East to computer port 1 and TX-West to computer port 2.

If this is a half duplex protocol, you can also monitor the traffic
with a single serial port and two diodes. Connect the cathodes of
these diodes to the snooping port Rx line. Connect the anodes of these
diodes to the Tx-East resp. TX-West signals.

>Write a very simple serial reader. Set the ports up raw (see my post
>from a couple of day ago). Loop, doing a blocking read on each character
>on the serial port. Print this out with a timestamp.

If you do the time stamping in user mode, the accuracy of the time
stamp is questionable. If you timestamp in the ISR (e.g. by reading
the TSC on Pentium systems), quite accurate timings can be extracted.

Of course the traditional way is to use a dual channel oscilloscope
and measure the time of Tx/Rx switchover.

Paul

Relevant Pages

  • Re: Serial port monitor
    ... > with a single serial port and two diodes. ... > these diodes to the snooping port Rx line. ... Print this out with a timestamp. ... As long as there is no context switch between the read and the timestamp ...
    (comp.arch.embedded)
  • Re: Driver design thoughts
    ... >The timestamp (absolute time) is really received through a serial port. ... If you wired up your PPS signal to one of those ...
    (microsoft.public.development.device.drivers)
  • Re: Driver design thoughts
    ... The timestamp is really received through a serial port. ... received in the form of PPS pulse in one PIN of ... Since I need to precisely detect this pulse, do I now need a "real ...
    (microsoft.public.development.device.drivers)