Xircom realport in 8.1-RELEASE - how do I determine proper cbb.start_memory ?

[George Sanders]

It appears that many PCMCIA network cards no longer work in FreeBSD - this is 
documented here:

http://www.freebsd.org/cgi/query-pr.cgi?pr=115623

However there appears to be a workaround, wherein one sets their 
hw.cbb.start_memory value manually.  Suggested values for xircom cards are:

sysctl hw.cbb.start_memory=0xf4800000
sysctl hw.cbb.start_memory=0x30000000

However, neither of these values work for me, and I continue to get this kind of 

error:

dc1: No station address in CIS!

etc.

I am happy to use this workaround, I just wonder how do I determine the proper 
value for this sysctl ?

My xl0 network interface works, and I see that its settings are:

port 0xec80-0xecff mem 0xf8fffc00-0xf8fffc7f

How do I compute the proper sysctl setting for my xircom realport cards ?  (I 
have two of them to insert simultaneously)

Thanks.