comments on adjusting the clock

[Hal Murray]

(I'll be out for the next day or so, so don't expect prompt answers.  Sorry 
this isn't cleaner.  Gotta run.)

There may be bogus stuff in here.  Measure twice, edit once.

I think the whole doubletime_t was a wild goose chase.

The claimed reason was precision.  A double has 53 bits.  We are interrested 
in adjustments, not absolute values.  If we are taking a huge adjustment (31 
bits), that still leaves 20 bits of fractional second.  That's microseconds.  
I think that's good enough to get started.  Most adjustments are small 
fractions of a second.  If we start with 53 bits, we will be throwing away 
almost half of them when we convert to l_fp.

Is there any reason we are using doubles?  Why not l_fp?  (There may be some 
statistical math that is easier with floats.)  Maybe we could carry a 
parallel version in l_fp if we want to preserve precision.

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There are two modules that both adjust the system clock.
  libntp/clockwork.c and 
  libntp/systime.c

There are two ways to adjust the clock:
  adj_systime is in ./libntp/systime.c and 
  ntp_adjtime_ns is in ./libntp/clockwork.c

I haven't figured out what's going on.  It doesn't look good.

The doubletime_t stuff is only used in one of them.

All the calls to adj_systime pass in adjtime.  Why?
(I assume history that nobody has cleaned up yet.)

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./include/ntp_syscall.h checks STA_NANO and defines ntp_error_in_seconds
The comment mentions maxerror and esterror

It's only used in ntpd/ntp_control.c, but there it is used 5 times.
  It calls ntp_adjtime directly, under HAVE_KERNEL_PLL
  I think it could just call ntp_adjtime_ns

----------

There is some ugly stuff in start_kern_loop involving 
ntp_adjtime_error_handler

I think it's trying to make a run time test to see if ntp_adjtime actually 
works.  I'm a bit surprised there isn't a cleaner way.

--------


ntp_adjtime
ntp_error_in_seconds

libntp/systime.c          adj_systime
libntp/clockwork.c    ntp_adjtime_ns  called by ntp_loopfilter

ntp_adjtime_error_handler
  I think it's for in-kernel PLL
pll_trap




-- 
These are my opinions.  I hate spam.