PIIXPCIB(4) OpenBSD Programmer's Manual (i386) PIIXPCIB(4)NAMEpiixpcib - 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
Pentium 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 ALSOcpu(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
after switching power state. The reason is that there seems to be no
reliable 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 4.9 October 8, 2007 OpenBSD 4.9
