[time-nuts] Modern motherboard with RS232 port

Bob Camp lists at rtty.us
Sun Aug 19 22:02:03 EDT 2012


Hi

But you still need:

1) Porting of the kernel timing stuff to the ARM6 architecture. Once it's ported, you need it debugged and fine tuned.
2) The low level drivers in NTP ported to the ARM6 i/o setup. They also need some work to reduce latency.
3) The timing work on the USB to Ethernet interface.

I'm not knocking the pi, it's a fine little gizmo. However it's just that, a little gizmo, at this point. There's still a lot of work to be done on it. Getting a solid implementation of anything takes significant work. There are other reasonably cheap / low power platforms where people have already put in the man years to ring things out.

Bob

On Aug 19, 2012, at 9:49 PM, bownes <bownes at gmail.com> wrote:

> It comes w ntp out of the box if you run fedora. 
> 
> 
> 
> On Aug 19, 2012, at 20:21, Bob Camp <lists at rtty.us> wrote:
> 
>> Hi
>> 
>> 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.
>> 
>> Bob
>> 
>> 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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>> 
>> 
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