You need the latest Splitter from "http://www.mkgmap.org.uk/splitter/"
Get the latest Snapshot of mkgmap from "http://www.mkgmap.org.uk/snapshots/"
If you like, choose a *.typ file of your choise. I used Computerteddy's "teddy.typ" "http://openstreetmap.teddynetz.de:81/latest/new/teddy.typ"

This is my bash to generate a route-able Map for Poland & Germany on a Garmin etrex:
(You can add more *.pbf to cover more countries/regions)

#!bin/bash
wget -t0 -c http://download.geofabrik.de/osm/europe/poland.osm.pbf
cp poland.osm.pbf working/
wget -t0 -c http://download.geofabrik.de/osm/europe/germany.osm.pbf
cp germany.osm.pbf working/

cd working/
java -enableassertions -Xmx4096M -jar ../splitter.jar --max-nodes=240000 --output=xml germany.osm.pbf poland.osm.pbf

java -enableassertions -Xmx4096M -jar ../mkgmap.jar --max-jobs --name-tag-list="name,name:de,int_name" --generate-sea=no-mp --family-id=1331 --product-id=1 --net --tdbfile --route --reduce-point-density=10 --add-pois-to-areas --road-name-pois=0x640a --draw-priority=25 --latin1 --make-opposite-cycleways --remove-short-arcs --verbose --mapname="MyMap20111101" --gmapsupp -c template.args teddy.typ

cd ..
## End