By default, the AlphaServer 400 firmware used by Avanti enumerates the KZPAA controllers first, then the KZPCA controllers, regardless of the card’s position on the PCI bus.  This means that in a two-controller system consisting of KZPAA and KZPCA controllers, the KZPAA is assigned PKA and the KZPCA is assigned PKB, regardless of the PCI slot chosen in the Avanti configuration.

In a more elaborate example with 4 SCSI controllers:

There is a firmware setting to change this behavior:

>>> set bus_probe_algorithm new
>>> init

after which the controllers will be enumerated in PCI bus order.

The original settings can be restored using the following firmware commands.

>>> set bus_probe_algorithm old
>>> init