PIIX4 ISA bridges
piixpcib* at pci?
isa* at piixpcib?
driver supports Intel 82371AB and
82440MX PIIX4 ISA bridges.
Besides the core functionality, the piixpcib
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
sysctl is less than or equal
to 50, and into high power state if it is greater than 50.
driver first appeared in
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