---
name: "pchb"
section: "4"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/pchb"
---

# pchb(4)

PCI-Host Bridge

## 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)](/random/4.md) 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)](/intro/4.md), [pci(4)](/pci/4.md), [random(4)](/random/4.md)

## 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).