If the Tru64 system being ported to Avanti does not already use a DE435 or DE500 NIC, then a new kernel will need to be built which includes 'tu' support before it recognizes Avanti's DE435/500 hardware.  There is a section on doing this in the Tru64 Administration Guide.

•Tru64 UNIX V5.1B System Admin Guide AA-RH9FE-TE
Sections 4.6.1, 4.6.2 and 4.6.2 - Building the Kernel under various circumstances.

Or

•Tru64 UNIX V4.0F System Admin Guide AA-PS2RF-TE
Sections 5.4.1, 5.4.2 and 5.4.3 - Building the Kernel under various circumstances.