1 .\" $NetBSD: time.9,v 1.1 1995/11/25 21:24:53 perry Exp $
3 .\" Copyright (c) 1994 Christopher G. Demetriou
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42 .Nd system time variables
46 .Va extern struct timeval boottime ;
48 .Va extern volatile struct timeval mono_time ;
50 .Va extern struct timeval runtime ;
52 .Va extern struct timeval time ;
57 variable is the system's
64 system call and by periodic clock interrupts.
68 variable holds the system boot time. It is set from
70 at system boot, and is updated when the system time is adjusted
76 variable holds the time that the system switched to the
78 It is set after each context switch,
79 and is updated when the system time is adjusted with
83 is used for system accounting, it is set with the high-resolution
85 function, rather than being copied from
90 variable is a monotonically increasing system clock. It is set
93 at boot, and is updated by the periodic timer interrupt. (It is
97 All of these variables contain times
98 expressed in seconds and microseconds since midnight (0 hour),
101 Clock interrupts should be blocked
102 when reading or writing
106 because those variables are updated by
110 function can be used to read the
112 variable in an atomic manner. There is no equivalent
113 function for accessing
119 variables may be read and written without special precautions.
121 It should be noted that due to the differences in how the time values
126 are updated, comparing the results of the two routines
127 may result in a time value that appears to go backwards.
128 This can be avoided by consistently using one function or the other
129 for use in any given context.
134 .\" .Xr hardclock 9 ,
138 The notion of having a single
140 variable obviously would not be appropriate in multiprocessor systems.