Lines Matching +full:light +full:- +full:weight
5 .\" ----------------------------------------------------------------------------
6 .\" "THE BEER-WARE LICENSE" (Revision 42):
9 .\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
10 .\" ----------------------------------------------------------------------------
16 .A "Poul-Henning Kamp" "The FreeBSD Project"
18 The FreeBSD timecounters are an architecture-independent implementation
21 multiplication to canonical timescales based on micro- or nano-seconds
23 synchronisation. Timecounters are implemented using lock-less
24 stable-storage based primitives which scale efficiently in SMP
80 for instance transport or consumption of a substance at a well-known
90 sun-dial Earths rotation about its axis.
94 atomic Quantum-state transitions in atoms.
108 with an error less than �2 cdot 10 sup{-15}� [DMK2001] with commercially
109 available products doing better than �1 cdot 10 sup{-14}� [AG2002].
137 Earth. This resulted in time-intervals being very unwieldy business,
140 Eventually the new leap-second method were introduced in 1972.
149 UTC is defined basically the same way, but every so often a leap-second
161 and measurement company formerly known as ``Hewlett-Packard'') which
162 count for as much as 85% of the combined weight.
164 The majority of the remaining weight is assigned to a handful of big
165 custom-design units like the PTB2 and NIST7.
172 The perceived wisdom of leap-seconds have been gradually decreasing
173 in recent years, as devices and products with built-in calendar
181 as the count of standard seconds since 00:00:00 01-01-1970 UTC,
182 ignoring the leap-seconds. This definition has never been perceived
193 deficiency by transmitting the UTC-TAI offset as part of the protocol.
197 ``timespec''. Both of these formats are two-component structures
206 t3.tv_sec = t1.tv_sec - t2.tv_sec;
207 t3.tv_nsec = t1.tv_nsec -
211 t3.tv_nsec -= 1000000000;
213 t3.tv_sec--;
238 Resolution in clocks is simply a matter of the step-size of the
264 representation as the diameter of the bullet-hole is not correct,
267 gets too quantum-mechanical-oid to serve the instructional purpose.
275 On the x-axis we have time and on the y-axis how wrong the clock
289 devices, once you get into the �10 cdot 10 sup{-15}� territory
295 This particularly becomes an issue with space-based atomic standards
350 mostly a question of the resolution and steer-ability requirements.
366 chosen hardware and this hardware might be the GHz range CPU-clock.
375 �2 sup{32} / (2 sup{32}-1)� �=� 1.000 Hz
392 �2 sup{64} / (2 sup{64}-1)� �=� 1.000 Hz
411 timespec formats is that it is a binary number, not a pseudo-decimal
427 u = bt1->frac;
428 bt3->frac = bt1->frac + bt2->frac;
429 bt3->sec = bt1->sec + bt2->sec;
430 if (u > bt3->frac)
431 bt3->sec += 1;
446 ts->tv_sec = bt->sec;
447 ts->tv_nsec =
449 (uint32_t)(bt->frac >> 32)) >> 32;
460 bt->sec = ts->tv_sec;
463 bt->frac = ts->tv_nsec *
522 The delta-count operation is straightforward subtraction, but we
523 need to logically AND the result with a bit-mask with the same number
529 Delta Count = (Count sub{now} - Count sub{ref}) ~ BITAND ~ mask
550 Delta Count = (Count sub{now} - Count sub{ref}) ~ BITAND ~ mask
589 This quasi-decimal number is a bit of a square peg in our round binary
600 within an factor of a million of the �10 sup{-15}� performance level
606 In this case the correction may be as large as \(+- 5000 PPM which
607 leaves us room to multiply with about 850 in a multiply-before-divide
614 A divide-before-multiply approximation necessarily results in a loss
624 of the requested change, or �1.06 cdot 10 sup -14� per nanosecond
688 This would however be a very heavy-handed approach. First of
696 A pseudo-stable-storage with generation count method has been
712 meta-data.
715 This scheme has an inherent risk that a process may be de-scheduled for
731 gen = th->th_generation;
734 gen != th->th_generation);
766 instruction(-sequence).
779 The problem with this device is that it only has 8bit bus-width,
784 Obviously, on multi-CPU systems this cannot be done without some
815 counter'' called ``TSC'' in official data-sheets.
816 This is basically a on-CPU counter, which counts at the rate
839 Another wiggle for the TSC is that it is not usable on multi-CPU
850 The ACPI specification finally brings some light:
857 The reason for this odd-ball frequency has to be sought in the ghastly
867 have failed to provide latching suitable to avoid meta-stability
874 latched by examining the width of a histogram over read delta-values.
884 One example of this is the Loran-C receiver designed by Prof. Dave Mills
887 implements the software-half of the receiver has properly initialised
888 and locked onto a Loran-C signal.
914 a precision of \(+- 10 nanoseconds \(+- one count which in practice
915 averages out to roughly \(+- 15 nanoseconds\**:
957 The source-code is located almost entirely in the kernel source file
966 open source license or the even more free ``Beer-ware'' license.
985 Various micro-optimizations, mostly to compensate for inadequate
1003 NTP, for lending out the neglected twin Loran-C receiver and for
1013 The staff at the NELS Loran-C control station in B�, Norway for providing
1014 information about step-changes.
1016 The staff at NELS Loran-C station Ei�e, Faeroe
1037 Poul-Henning Kamp
1041 "A computer-controlled LORAN-C receiver for precision timekeeping."
1043 Electrical Engineering Department Report 92-3-1, University of Delaware, March 1992, 63 pp.
1046 …ime and Time Interval (PTTI) Applications and Planning Meeting (Reston VA, November 2000), 431-439.
1050 Mills, D.L., and P.-H. Kamp.
1051 …ime and Time Interval (PTTI) Applications and Planning Meeting (Reston VA, November 2000), 423-430.
1066 This ``gee-wiz'' kind of article in Dr. Dobbs Journal is a good place to