tail head cat sleep
QR code linking to this page

Manual Pages  — AHD


ahd – Adaptec PCI/PCI-X Ultra320 SCSI host adapter driver



To compile this driver into the kernel, place the following lines in your kernel configuration file: device pci device scbus device ahd

To compile in debugging code: options AHD_DEBUG options AHD_DEBUG_OPTS=<bitmask of options> options AHD_REG_PRETTY_PRINT

To configure one or more controllers to assume the target role: options AHD_TMODE_ENABLE=<bitmask of units>

Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):



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

Driver features include support for narrow and wide busses, fast, ultra, ultra2, ultra160, and ultra320 synchronous transfers, packetized transfers, tagged queueing, 512 SCB's, and target mode.

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
0x0001Show miscellaneous information
0x0002Show sense data
0x0004Show Serial EEPROM contents
0x0008Show bus termination settings
0x0010Show host memory usage
0x0020Show SCSI protocol messages
0x0040Show mode pointer of the chip register window
0x0080Show selection timeouts
0x0100Show FIFO usage messages
0x0200Show Queue Full status
0x0400Show SCB queue status
0x0800Show inbound packet information
0x1000Show S/G list information
0x2000Enable extra diagnostic code in the firmware

The AHD_REG_PRETTY_PRINT option compiles in support for human-readable bit definitions for each register that is printed by the debugging code. However, it also bloats the compiled size of the driver by approximately 215KB.

Individual controllers may be configured to operate in the target role through the AHD_TMODE_ENABLE configuration option. The value assigned to this option should be a bitmap of all units where target mode is desired. For example, a value of 0x25 would enable target mode on units 0, 2, and 5. Note that target mode is only supported for ultra160 speeds and below.

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 adapter's SCSI ID.


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


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


The ahd driver first appeared in FreeBSD 4.7 .


The ahd driver, the AIC7xxx sequencer-code assembler, and the firmware running on the aic79xx chips was written by Justin T. Gibbs. This manual page is based on the ahc(4) manual page.


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.

AHD (4) July 4, 2004

tail head cat sleep
QR code linking to this page

Please direct any comments about this manual page service to Ben Bullock. Privacy policy.

As soon as we started programming, we found to our surprise that it wasn't as easy to get programs right as we had thought. Debugging had to be discovered. I can remember the exact instant when I realized that a large part of my life from then on was going to be spent in finding mistakes in my own programs.
— Maurice Wilkes