[ntp:questions] Adjust serial device speed in ACTS refclock driver?

Harlan Stenn stenn at ntp.org
Mon Oct 6 00:52:14 UTC 2014


Rich Wales writes:
> Is there any way, in the ACTS refclock driver, to specify the speed at
> which the modem's serial port should be opened?

I'm not seeing one...

> The source code (ntpd 4.2.7p475) appears to use a hard-coded speed of
> 19,200 bits/sec (ntpd/refclock_acts.c, line 138).  I was unable to
> connect to the NIST time service at all -- the service picked up the
> line, but I heard a lot of chaotic noise (suggesting a futile attempt
> to negotiate a connection) until the driver eventually timed out and
> hung up.

The docs say it connects at 9600, so there is a discrepancy there...

> I can connect without any problems at all, however, if I dial up
> manually (using "cu -s 1200 -l /dev/acts0").
> 
> I changed B19200 to B1200 in the ACTS driver, and the resulting ntpd
> was able to connect and get valid time info from NIST.  But I'd prefer
> a solution, if at all possible, that doesn't require changing the
> source code.  Any thoughts?

I know several folks have been using the current driver without
problems, so I'm curious about what's going on here.

I also know that some modems will auto-baud, but that might not matter.
Some will allow the modem connect speed to be different from what is
used by the serial connection to the modem.

The NMEA refclock uses mode bits 4/5/6 to control the baudrate, but I
don't know if 8 baudrate values will be enough.  Should be OK, but we
might be using all the values.

I assume you've seen:

 http://support.ntp.org/Support/ConfiguringModemRefclocks
 http://support.ntp.org/Support/ConfiguringNMEARefclocks

and neither of those will likely be much help, but if you or anybody
else sees ways to improve these, please feel free...

H


More information about the questions mailing list