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

# ahd(4)

Adaptec PCI/PCI-X AIC79xx-based Ultra320 SCSI interface

## NAME

**ahd** – Adaptec PCI/PCI-X AIC79xx-based Ultra320 SCSI interface

## SYNOPSIS

**ahd\* at pci?**

## DESCRIPTION

**ahd** provides access to the SCSI bus(es) connected to Adaptec AIC79xx host adapter chips.

**ahd** supports narrow and wide buses; synchronous and asynchronous operation; fast, ultra, ultra2, ultra160, and ultra320 (packetized) transfers; tagged queuing and 512 SCBs.

**ahd** does not support target mode operation.

The **ahd** driver supports the following:

- Adaptec AIC7901 host adapter chip

- Adaptec AIC7901A host adapter chip

- Adaptec AIC7902 host adapter chip

- Adaptec 29320 host adapter

- Adaptec 39320 host adapter

- Many motherboards with on-board SCSI support

To compile in debugging code:

**option** **AHD\_DEBUG** **option** **AHD\_DEBUG\_OPTS=\<bitmask** **of** **options\>**

The AHD\_DEBUG\_OPTS option is used to control which diagnostic messages are printed to the console when AHD\_DEBUG is enabled. Logically OR the following bits together:

| | |
| --- | --- |
| *Value* | *Function* |
| 0x0001 | Show miscellaneous information |
| 0x0002 | Show sense data |
| 0x0004 | Show Serial EEPROM contents |
| 0x0008 | Show bus termination settings |
| 0x0010 | Show host memory usage |
| 0x0020 | Show SCSI protocol messages |
| 0x0040 | Show mode pointer of the chip register window |
| 0x0080 | Show selection timeouts |
| 0x0100 | Show FIFO usage messages |
| 0x0200 | Show Queue Full status |
| 0x0400 | Show SCB queue status |
| 0x0800 | Show inbound packet information |
| 0x1000 | Show S/G list information |
| 0x2000 | Enable extra diagnostic code in the firmware |

Per target configuration performed in the SCSI-Select menu, accessible at boot, is honored by this driver. This includes synchronous/asynchronous transfers, maximum synchronous negotiation rate, wide transfers, disconnection, and the host adapters SCSI ID.

## SEE ALSO

[ahc(4)](/ahc/4.md), [cd(4)](/cd/4.md), [ch(4)](/ch/4.md), [intro(4)](/intro/4.md), [pci(4)](/pci/4.md), [scsi(4)](/scsi/4.md), [sd(4)](/sd/4.md), [st(4)](/st/4.md), [uk(4)](/uk/4.md)

## HISTORY

The **ahd** driver was ported from FreeBSD 4.7 and first appeared in OpenBSD 3.6.

## AUTHORS

The **ahd** driver, the AIC7xxx sequencer-code assembler, and the firmware running on the aic79xx chips was written by Justin T. Gibbs.

OpenBSD port by Milos Urbanek, Kenneth R. Westerback & Marco Peereboom.