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28 .\" $FreeBSD: src/share/man/man7/clocks.7,v 1.9.2.5 2001/12/17 11:30:15 ru Exp $
35 .Nd various system timers
40 is not part of the application interface in
43 There are many different real and virtual (timekeeping) clocks with
44 different frequencies:
45 .Bl -bullet -offset XXX
47 The scheduling clock. This is a real clock with frequency that
48 happens to be 100. It isn't available to applications.
50 The statistics clock. This is a real clock with frequency that
51 happens to be 128. It isn't directly available to applications.
55 This is a virtual clock with a frequency that happens to be 128. Its
56 actual frequency is given by the macro
60 may be floating point. Don't use
64 It is feeble compared with
66 It is provided for ANSI conformance. It is implemented by calling
68 and throwing away information and resolution.
72 This is a virtual clock with a frequency that happens to be 128. Its
73 actual frequency is given by the macro
75 (deprecated; don't use) and by
76 .Fn sysconf SC_CLK_TCK
79 Note that its frequency may be different from
85 It is feeble compared with
89 It is provided for POSIX
90 conformance. It is implemented by calling
94 and throwing away information and resolution.
96 The profiling clock. This is a real clock with frequency 1024.
101 Applications should determine its actual frequency using
103 or by reading it from the header in the profiling data file.
105 The mc14618a clock. This is a real clock with a nominal frequency of
106 32768. It is divided down to give the statistic clock and the profiling
107 clock. It isn't available to applications.
109 The microseconds clock. This is a virtual clock with frequency
110 1000000. It is used for most timekeeping in
118 etc... This is the clock that should normally be used
123 The i8254 clock. This is a real clock/timer with a nominal frequency of
124 1193182. It is divided down to give the scheduling clock. It isn't
125 available to applications.
127 The TSC clock (64-bit register) on fifth-generation or later x86 systems.
128 This is a real clock with a frequency that is equivalent to the number of
129 cycles per second of the CPU(s).
130 Its frequency can be found using the sysctl
134 It is used to interpolate between values of the scheduling clock.
135 It is only available to applications in a purely machine-dependent manner.
137 The HPET (High Precision Event Timers).
138 Only main counter is used currently.
139 This CPU timer is expected to be faster than ACPI-fast24 and ACPI-safe,
140 so it should be given higher priority.
141 HPET is not enabled by default.
142 To enable it, you should add
143 .Li debug.acpi.enabled="hpet"
145 .Pa /boot/loader.conf .
146 If the HPET is detected and attached,
147 .Va kern.cputimer.name
154 isn't 1000000 then the application is probably using the wrong clock.
167 This man page has been written by
169 after a description posted by