PCHB(4)

NAME
pchb - PCI-Host Bridge

SYNOPSIS
pchb* at pci?
pci* at pchb?

DESCRIPTION
The pchb driver provides support for PCI-Host adapter-specific functions. Support is provided for the following devices:

i450 PCIset (Orion)
    Supports additional PCI buses.

Reliance Computer ROSB4, CNB20HE, CNB20LE
    Supports additional PCI buses.

i82424ZX (Saturn)
    Disables CPU-PCI write posting.

i82443BX
    Provides workaround for the following errata: "An incorrect address may be driven on the DRAM bus, resulting in memory data being fetched from the wrong location."

i82810/810E, i82815/815E, i82820, i82840
    Supports the random numbers generator, supplying random bytes from the system's thermal noise. Driven by periodic checks for available data from the generator, it supplies entropy to the random(4) driver for common usage.

On amd64 and i386 systems, most PCI devices of class Bridge and sub-class Bridge Host are supported just as PCI attachment points. A few other system control devices not listed here are supported by pchb.

The macppc port supports several Apple and Motorola bridges.

SEE ALSO
intro(4), pci(4), random(4)

HISTORY
Random number generator support first appeared in OpenBSD 2.7.

AUTHORS
Support for true RNG present on i82810 chips was added by Michael Shalayeff <mickey@openbsd.org>.

BUGS
Real RNG probe should fix the PCI scanning loop so it would find the Firmware Hub (i82802) which actually contains the RNG device and probe it as a real PCI device (i.e., common PCI registers are there).