timex.h 6.7 KB

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  1. /*****************************************************************************
  2. * *
  3. * Copyright (c) David L. Mills 1993 *
  4. * *
  5. * Permission to use, copy, modify, and distribute this software and its *
  6. * documentation for any purpose and without fee is hereby granted, provided *
  7. * that the above copyright notice appears in all copies and that both the *
  8. * copyright notice and this permission notice appear in supporting *
  9. * documentation, and that the name University of Delaware not be used in *
  10. * advertising or publicity pertaining to distribution of the software *
  11. * without specific, written prior permission. The University of Delaware *
  12. * makes no representations about the suitability this software for any *
  13. * purpose. It is provided "as is" without express or implied warranty. *
  14. * *
  15. *****************************************************************************/
  16. /*
  17. * Modification history timex.h
  18. *
  19. * 29 Dec 97 Russell King
  20. * Moved CLOCK_TICK_RATE, CLOCK_TICK_FACTOR and FINETUNE to asm/timex.h
  21. * for ARM machines
  22. *
  23. * 9 Jan 97 Adrian Sun
  24. * Shifted LATCH define to allow access to alpha machines.
  25. *
  26. * 26 Sep 94 David L. Mills
  27. * Added defines for hybrid phase/frequency-lock loop.
  28. *
  29. * 19 Mar 94 David L. Mills
  30. * Moved defines from kernel routines to header file and added new
  31. * defines for PPS phase-lock loop.
  32. *
  33. * 20 Feb 94 David L. Mills
  34. * Revised status codes and structures for external clock and PPS
  35. * signal discipline.
  36. *
  37. * 28 Nov 93 David L. Mills
  38. * Adjusted parameters to improve stability and increase poll
  39. * interval.
  40. *
  41. * 17 Sep 93 David L. Mills
  42. * Created file $NTP/include/sys/timex.h
  43. * 07 Oct 93 Torsten Duwe
  44. * Derived linux/timex.h
  45. * 1995-08-13 Torsten Duwe
  46. * kernel PLL updated to 1994-12-13 specs (rfc-1589)
  47. * 1997-08-30 Ulrich Windl
  48. * Added new constant NTP_PHASE_LIMIT
  49. * 2004-08-12 Christoph Lameter
  50. * Reworked time interpolation logic
  51. */
  52. #ifndef _LINUX_TIMEX_H
  53. #define _LINUX_TIMEX_H
  54. #include <uapi/linux/timex.h>
  55. #define ADJ_ADJTIME 0x8000 /* switch between adjtime/adjtimex modes */
  56. #define ADJ_OFFSET_SINGLESHOT 0x0001 /* old-fashioned adjtime */
  57. #define ADJ_OFFSET_READONLY 0x2000 /* read-only adjtime */
  58. #include <linux/compiler.h>
  59. #include <linux/types.h>
  60. #include <linux/param.h>
  61. unsigned long random_get_entropy_fallback(void);
  62. #include <asm/timex.h>
  63. #ifndef random_get_entropy
  64. /*
  65. * The random_get_entropy() function is used by the /dev/random driver
  66. * in order to extract entropy via the relative unpredictability of
  67. * when an interrupt takes places versus a high speed, fine-grained
  68. * timing source or cycle counter. Since it will be occurred on every
  69. * single interrupt, it must have a very low cost/overhead.
  70. *
  71. * By default we use get_cycles() for this purpose, but individual
  72. * architectures may override this in their asm/timex.h header file.
  73. * If a given arch does not have get_cycles(), then we fallback to
  74. * using random_get_entropy_fallback().
  75. */
  76. #ifdef get_cycles
  77. #define random_get_entropy() ((unsigned long)get_cycles())
  78. #else
  79. #define random_get_entropy() random_get_entropy_fallback()
  80. #endif
  81. #endif
  82. /*
  83. * SHIFT_PLL is used as a dampening factor to define how much we
  84. * adjust the frequency correction for a given offset in PLL mode.
  85. * It also used in dampening the offset correction, to define how
  86. * much of the current value in time_offset we correct for each
  87. * second. Changing this value changes the stiffness of the ntp
  88. * adjustment code. A lower value makes it more flexible, reducing
  89. * NTP convergence time. A higher value makes it stiffer, increasing
  90. * convergence time, but making the clock more stable.
  91. *
  92. * In David Mills' nanokernel reference implementation SHIFT_PLL is 4.
  93. * However this seems to increase convergence time much too long.
  94. *
  95. * https://lists.ntp.org/pipermail/hackers/2008-January/003487.html
  96. *
  97. * In the above mailing list discussion, it seems the value of 4
  98. * was appropriate for other Unix systems with HZ=100, and that
  99. * SHIFT_PLL should be decreased as HZ increases. However, Linux's
  100. * clock steering implementation is HZ independent.
  101. *
  102. * Through experimentation, a SHIFT_PLL value of 2 was found to allow
  103. * for fast convergence (very similar to the NTPv3 code used prior to
  104. * v2.6.19), with good clock stability.
  105. *
  106. *
  107. * SHIFT_FLL is used as a dampening factor to define how much we
  108. * adjust the frequency correction for a given offset in FLL mode.
  109. * In David Mills' nanokernel reference implementation SHIFT_FLL is 2.
  110. *
  111. * MAXTC establishes the maximum time constant of the PLL.
  112. */
  113. #define SHIFT_PLL 2 /* PLL frequency factor (shift) */
  114. #define SHIFT_FLL 2 /* FLL frequency factor (shift) */
  115. #define MAXTC 10 /* maximum time constant (shift) */
  116. /*
  117. * SHIFT_USEC defines the scaling (shift) of the time_freq and
  118. * time_tolerance variables, which represent the current frequency
  119. * offset and maximum frequency tolerance.
  120. */
  121. #define SHIFT_USEC 16 /* frequency offset scale (shift) */
  122. #define PPM_SCALE ((s64)NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC))
  123. #define PPM_SCALE_INV_SHIFT 19
  124. #define PPM_SCALE_INV ((1LL << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \
  125. PPM_SCALE + 1)
  126. #define MAXPHASE 500000000L /* max phase error (ns) */
  127. #define MAXFREQ 500000 /* max frequency error (ns/s) */
  128. #define MAXFREQ_SCALED ((s64)MAXFREQ << NTP_SCALE_SHIFT)
  129. #define MINSEC 256 /* min interval between updates (s) */
  130. #define MAXSEC 2048 /* max interval between updates (s) */
  131. #define NTP_PHASE_LIMIT ((MAXPHASE / NSEC_PER_USEC) << 5) /* beyond max. dispersion */
  132. /*
  133. * kernel variables
  134. * Note: maximum error = NTP sync distance = dispersion + delay / 2;
  135. * estimated error = NTP dispersion.
  136. */
  137. extern unsigned long tick_usec; /* USER_HZ period (usec) */
  138. extern unsigned long tick_nsec; /* SHIFTED_HZ period (nsec) */
  139. /* Required to safely shift negative values */
  140. #define shift_right(x, s) ({ \
  141. __typeof__(x) __x = (x); \
  142. __typeof__(s) __s = (s); \
  143. __x < 0 ? -(-__x >> __s) : __x >> __s; \
  144. })
  145. #define NTP_SCALE_SHIFT 32
  146. #define NTP_INTERVAL_FREQ (HZ)
  147. #define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
  148. extern int do_adjtimex(struct __kernel_timex *);
  149. extern int do_clock_adjtime(const clockid_t which_clock, struct __kernel_timex * ktx);
  150. extern void hardpps(const struct timespec64 *, const struct timespec64 *);
  151. int read_current_timer(unsigned long *timer_val);
  152. /* The clock frequency of the i8253/i8254 PIT */
  153. #define PIT_TICK_RATE 1193182ul
  154. #endif /* LINUX_TIMEX_H */