Can someone tell me what the correct syntax is for the avp_url command?

I've been at this for hours and it's driving me CRAZY!

this:
modparam("avpops","avp_url","unixodbc://user:password@127.0.0.1/database")
gives:
unixodbc:extract_error: unixodbc:SQLDriverConnect=IM002:1:0:[unixODBC][Driver Manager]Data source name not found, and no default driver specified

this:
modparam("avpops","avp_url","unixodbc://dsn" )
gives:
core:new_db_id: error while parsing database URL: unixodbc://dsn

and I've tried about a HUNDRED other combinations.

Doug.