AHD(4)

💅 AHD(4) — Kernel Interfaces Manual 🎀

okay so bestie, gather round, because we're talking about ahd(4) — the Adaptec PCI/PCI-X Ultra320 SCSI host adapter driver. yes it's a mouthful. no you don't have to memorise it. let's go ✨

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🌸 NAME 🌸

ahd — the Adaptec PCI/PCI-X Ultra320 SCSI host adapter driver. that's it, that's the name, she's iconic 👑

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🦋 SYNOPSIS 🦋

so like, if you wanna compile this driver into the kernel, you drop these lines into your kernel configuration file:

device pci
device scbus
device ahd

and if you're feeling extra and want the debugging code compiled in too:

options AHD_DEBUG
options AHD_DEBUG_OPTS=<bitmask of options>
options AHD_REG_PRETTY_PRINT

OR — and this is the low-effort slay route — you can just load the driver as a module at boot time by putting this line in loader.conf(5):

ahd_load="YES"

main character energy honestly 🫶

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💖 DESCRIPTION 💖

This driver gives you access to the SCSI bus(es) that are connected to Adaptec AIC79xx host adapter chips. literally its whole job 💅

Driver features include support for:

• narrow and wide busses
• fast, ultra, ultra2, ultra160, and ultra320 synchronous transfers
• packetized transfers
• tagged queueing
• 512 SCB's
• target mode

so many features. she's booked and busy 🔥

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🧚 the AHD_DEBUG_OPTS situation

The AHD_DEBUG_OPTS option is what controls which diagnostic messages get printed to the console when AHD_DEBUG is enabled. to pick your messages, logically OR the following bits together:

• 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

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🎀 the AHD_REG_PRETTY_PRINT situation

The AHD_REG_PRETTY_PRINT option compiles in support for human-readable bit definitions for each register that the debugging code prints. gorgeous, readable, a dream 🌈

however. it also bloats the compiled size of the driver by approximately 215KB. so like… she's pretty but she's thicc 😭 pick your battles.

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💜 per target configuration

Anything you set up per target in the SCSI-Select menu (accessible at boot) is honored by this driver. that includes:

• synchronous/asynchronous transfers
• maximum synchronous negotiation rate
• wide transfers
• disconnection
• the host adapter's SCSI ID

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✨ CONFIGURATION OPTIONS ✨

Wanna statically configure one or more controllers to assume the target role? okay bestie:

options AHD_TMODE_ENABLE <bitmask of units>

The value you assign to this option should be a bitmap of all units where you want target mode. for example:

• a value of 0x25 would enable target mode on units 0, 2, and 5
• a value of 0x8a enables it for units 1, 3, and 7

ngl the note here is important: controllers can also be dynamically configured through a device hint, which is documented below 👇

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🌟 BOOT OPTIONS 🌟

The following options are switchable by setting values in /boot/device.hints.

They are:

• hint.ahd.N.tmode_enable — a hint to define whether the SCSI target mode is enabled (0 — disabled, 1 — enabled).

that's the whole list, she's short and sweet 🍓

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🔥 HARDWARE 🔥

The ahd driver supports the following PCI/PCI-X parallel SCSI controllers:

• 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

if you own one of these, congrats, you're in the club 👑

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👀 SEE ALSO 👀

ahc(4), cd(4), da(4), sa(4), scsi(4)

go read those too, iykyk 📚

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🦄 HISTORY 🦄

The ahd driver first appeared in FreeBSD 4.7. vintage. she's got lore 💀

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💐 AUTHORS 💐

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

This manual page is based on the ahc(4) manual page. giving credit where credit is due 💖

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💀 BUGS 💀

okay so, the serious stuff, no jokes here:

• The current generation of 79xx chips do not support target mode in Ultra320 mode.
• Target mode in general has not been well tested in this driver.

so if you're relying on target mode, bestie, be careful — it's not a well-tested path 😭

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and that's the whole page!! mwah 💋 this was the AHD(4) page from the Kernel Interfaces Manual, and it's stamped Debian, dated September 29, 2025. go forth and SCSI responsibly 🦋✨