[time-nuts] Modern motherboard with RS232 port

Bob Camp lists at rtty.us
Mon Aug 20 00:21:28 UTC 2012


The pi doesn't have a conventional serial port. It does have a TTL serial on the 28 pin connector. There are also IRQ pins on the same connector. Since they go directly to the CPU chip, hardware latency should be pretty good. It should interface directly to a TTL output gps receiver like a LEA-6T. You probably would need to tune up a driver to get it to work. Since it's Linux, you should be able to get some sort of ntp running on it. AFIK there are no neat counters like on a 45xx board. You also don't have a well tuned ntp since it's LInux.


On Aug 19, 2012, at 1:31 PM, Chris Albertson <albertson.chris at gmail.com> wrote:

> On Sun, Aug 19, 2012 at 10:16 AM, bownes <bownes at gmail.com> wrote:
>> Why not just use a raspberry pi? Uses a whole 2w at idle. Ntp might bump
>> that  to 2.01.
> You certainly could run ntpd on that box.  But I wonder how the PPS is
> supported in hardware?   What is the standard deviation of interrupt
> latency on the DCD pin on the serial port.  Perhaps some one who has a "pi"
> could measure this.   All the data should be in the system log as each PPS
> is time stamped and written to the log.   If the DCD pin is polled you are
> not going to get decent results.  Maybe someone could read the PPS drive
> code.
> -- 
> Chris Albertson
> Redondo Beach, California
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