[ntp:hackers] Removing custom line discipline support from ntpd

Dave Hart hart at ntp.org
Sun Mar 20 12:49:08 UTC 2011

ntpd has support for several TTY line disciplines created or tweaked
for reference clock use.  Dr. Mills told me these haven't been used in
years and should be eradicated from the distribution.  These include
TTYCLK, used via ioctl(fd, I_PUSH, "clk") indirectly from
refclock_open(), which underlies LDISC_CLK, LDISC_CLKPPS, LDISC_ACTS.
Previously, ntpd "depredated" LDISC_CHU and LDISC_PPS, which have no

Each of the ones built on TTYCLK would stuff a timestamp after the
data received, recognized by ntpd by the last 8 bytes decoding to
within 1s of current time.

I propose to follow through by removing TTYCLK support from ntpd, but
leaving the LDISC_ flags defined but deprecated, to ease backporting
the latest drivers onto older systems where the flags might have
utility.  I also propose removing the related (and severely neglected)
standalone test utilities for CHU and TTYCLK disciplines.

Note the remaining LDISC_ flags would not be affected (LDISC_STD,

Are you aware of anyone likely to use 4.2.7 or later on a system which
provides a working clk line discipline module?

Dave Hart

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