[time-nuts] Recommendations for NTP server
John Ackermann N8UR
jra at febo.com
Fri May 5 18:35:54 UTC 2006
Glenn wrote:
>>>Is PPS kernel discipline compiled into the default FreeBSD kernel?
>>>
>>>
>>
>>No, but it's a pretty easy thing to turn on -- you add a line to the
>>config file and tell it to go. Pretty straightforward, *once* you find
>>the instructions.
>>
>>
>
>
> Where would I find these instructions?
It's in the FreeBSD users manual (or whatever it's called) which I found
at the FreeBSD web site. That gives general instructions for rebuilding
the kernel. I'm not sure if it specifically identifies the PPS flag or
not. On my 5.4 machine, it was adding:
# NTP PPS support
options PPS_SYNC
to the /usr/src/sys/i386/config/PPS_KERNEL file, which was copied from
the generic kernel config file. Then rebuild, specifying PPS_KERNEL as
the config file name. There's also an associated .hints file which
allows you to set the serial ports to low-latency mode by disabling the
FIFO in the 16550 UART chip; this can reduce jitter. I don't recall for
sure, but I *think* it's setting the second bit (ie, 0x1_) in the flags
field:
hint.sio.0.at="isa"
hint.sio.0.port="0x3F8"
hint.sio.0.flags="0x12"
John
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