.\"	$OpenBSD: cpu.4,v 1.16 2009/07/13 15:43:05 jmc Exp $
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.\" Copyright (c) 2004 Ted Unangst
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.Dd $Mdocdate: July 13 2009 $
.Dt CPU 4 i386
.Os
.Sh NAME
.Nm cpu
.Nd Central Processing Unit
.Sh SYNOPSIS
.Cd "cpu0 at mainbus?"
.Cd "cpu* at mainbus?"
.Sh DESCRIPTION
Several processor models have additional features that extend their base
functionality, such as power and frequency control or thermal monitoring.
.Sh FREQUENCY CONTROL
The
.Xr sysctl 3
hw.cpuspeed will return the current operating frequency of the processor
(on some processors this value may be an approximation).
If possible, speed may be adjusted by altering hw.setperf from 0 to 100,
representing percentage of maximum speed.
There are several possible implementations for setperf, all transparent
to the user.
In systems with more than one control capability, they are preferred in the
order given.
.Bl -tag -width tenletters
.It LongRun
Found on Transmeta Crusoe processors, offers frequency scaling with numerous
positions.
The processor dynamically adjusts frequency in response to load, the setperf
value is interpreted as the maximum.
.It EST
Enhanced SpeedStep found on Intel Pentium M processors,
offers frequency scaling with numerous positions.
.It SpeedStep
Found on some Intel Pentium 3 and newer mobile chips,
it is capable of adjusting frequency between a low and high value.
Only enabled on some chipsets.
.It TCC
Thermal Control Circuit found on Intel Pentium 4 and newer processors,
adjusts processor duty cycle in 12.5 percent increments.
.It PowerNow
Found on various AMD processors.
Currently only supports a limited set of models in the K6, K7, and K8 families.
.El
.Sh INSTRUCTION SET EXTENSIONS
The presence of extended instruction sets can be determined by
sysctl machdep.
.Bl -tag -width "tenletters"
.It osfxsr
Supports the fxsave instruction.
.It sse
Supports the SSE instruction set.
.It sse2
Supports the SSE2 instruction set.
.It xcrypt
Support the VIA AES encryption instruction set.
If this is supported, the
.Li libcrypto
EVP AES functions will automatically use this support.
.El
.Sh THERMAL MONITORING
The
.Xr sysctl 3
hw.sensors.cpu*.temp0 will return the current temperature reported by the
processor.
.Sh SEE ALSO
.Xr sysctl 8
.Sh BUGS
Due to the way in which thermal information is reported on Intel processors,
the temperature may be off by exactly +/-15 degrees C.
.Pp
For multiprocessor kernels with more than one CPU sensor,
processors will report identical temperatures
since the temperature is taken from the processor running the sensors update.