.\"	$OpenBSD: pchb.4,v 1.18 2013/07/16 16:05:49 schwarze Exp $
.\"
.\" Michael Shalayeff, 2000. Public Domain.
.\"
.Dd $Mdocdate: July 16 2013 $
.Dt PCHB 4
.Os
.Sh NAME
.Nm pchb
.Nd PCI-Host Bridge
.Sh SYNOPSIS
.Cd "pchb* at pci?"
.Cd "pci* at pchb?"
.Sh DESCRIPTION
The
.Nm
driver provides support for PCI-Host adapter-specific functions.
Support is provided for the following devices:
.Bl -tag -width Ds -offset indent
.It i450 PCIset (Orion)
Supports additional PCI buses.
.It Reliance Computer ROSB4, CNB20HE, CNB20LE
Supports additional PCI buses.
.It i82424ZX (Saturn)
Disables CPU-PCI write posting.
.It 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."
.It 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
.Xr random 4
driver for common usage.
.El
.Pp
On amd64 and i386 systems, most PCI devices of class
.Nm Bridge
and sub-class
.Nm Bridge Host
are supported just as PCI attachment points.
A few other system control devices not listed here are supported by
.Nm .
.Pp
The macppc port supports several Apple and Motorola bridges.
.Sh SEE ALSO
.Xr intro 4 ,
.Xr pci 4 ,
.Xr random 4
.Sh HISTORY
Random number generator support first appeared in
.Ox 2.7 .
.Sh AUTHORS
Support for true RNG present on i82810 chips was added by
.An Michael Shalayeff Aq Mt mickey@openbsd.org .
.Sh 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).