MirOS Manual: powernowhack(4)

POWERNOWHACK(4)         BSD Programmer's Manual (i386)         POWERNOWHACK(4)


     powernowhack - a pseudo-device for the AMD K7 PowerNow extension


     powernowhack0 at mainbus0 flags 0x0000


     MirOS provides support for the PowerNow function of recent AMD K7 proces-
     sors in order to save power or reduce heat. This is the kernel driver for
     setting the CPU speed via sysctl(8) using the hw.setperf knob and report-
     ing the result using the hw.cpuspeed control.

     Flags is a bit mask which specifies how the driver operates.

     0x8000  Override BIOS function.

             Do not look for a PST whose signature matches the CPUID. Instead,
             only use the specified PST.

     0x4000  Verbose operation.

             Print a list of all PSTs shown even if we find a PST matching the
             CPUID or the user has disabled the functionality by selecting PST

     0x0nnn  Select PST nnn.

             nnn is a hexadecimal value (three nibbles) specifying the number
             of the PST to use. PSTs are numbered linearily, starting from

             If nnn is 000 (default), additional output (the CPUID on which no
             signature matches) is shown and PST #001 is used.

             If nnn is FFF, the PowerNow function is disabled if no PST match-
             ing the CPUID is found or flag 0x8000 is also specified.


     0x0000  Default. Look for a matching PST, use first and list PSTs if none

     0x0FFF  Look for a matching PST, disable K7PN if none found.

     0x4FFF  List PSTs, then look for a matching PST and disable K7PN is none

     0x8002  Do not bother looking for a matching PST. Use the second PST.

     0xC002  Like 0x8002, but list all PSTs first.


     apm(4), intro(4), sysctl(3), sysctl(8)


     The powernowhack driver appeared in MirOS #8 and is based upon a third-
     party patch for NetBSD which has not yet made it into an official tree.


     powernowhack originated as a patch by Martin Vegiard <deadbug@gmail.com>,
     was integrated into OpenBSD by
     Ted Unangst <tedu@openbsd.org> and turned into a driver for MirOS by
     Thorsten Glaser <tg@mirbsd.org>.


     Using a mismatching PST may damage your CPU or induce fire in your com-

MirOS BSD #10-current            May 4, 2005                                 1

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