PIIXPCIB(4)           OpenBSD Programmer's Manual (i386)           PIIXPCIB(4)

NAME
     piixpcib - Intel PIIX4 ISA bridges

SYNOPSIS
     piixpcib* at pci?
     isa* at piixpcib?

DESCRIPTION
     The piixpcib driver supports Intel 82371AB and 82440MX PIIX4 ISA bridges.

     Besides the core functionality, the piixpcib driver provides support for
     the first generation of Intel's SpeedStep technology present in some Pen-
     tium III CPUs.  It allows the user to manually control CPU frequency with
     the sysctl(8) program.  The apmd(8) daemon can be used to automatically
     control CPU frequency.  SpeedStep provides two CPU power states, low and
     high.  The driver will switch the CPU into low power state if the
     hw.setperf sysctl is less than or equal to 50, and into high power state
     if it is greater than 50.

SEE ALSO
     cpu(4), ichpcib(4), intro(4), isa(4), pci(4), apmd(8), sysctl(8)

HISTORY
     The piixpcib driver first appeared in OpenBSD 4.2.

BUGS
     The driver sometimes fails to update the hw.cpuspeed sysctl correctly af-
     ter switching power state.  The reason is that there seems to be no reli-
     able way to determine CPU frequencies corresponding to low and high power
     states, so the driver has to rely on the p3_update_cpuspeed function to
     dynamically determine CPU speed after switching power state.  This seems
     to fail occasionally, especially if interrupt load of the system is high.
     Note that this bug is purely cosmetic.  Switching power state still works
     even if the CPU speed is displayed incorrectly.

OpenBSD 4.7                     October 8, 2007                              1
