There are a couple of minimal requirements to get DebWrt running on a router / embedded device:

• There should be a GNU/Linux kernel available which supports the router/embedded device ( OpenWrt )
• The device should have at least 350M(or more) of storage available for the Debian root filesystem ( external USB-stick or USB-disk )
• The device should have a reasonable amount of internal Memory ( 16M possible, 32M recommended) as well as an reasonable CPU ( 200MHz recommended )
• Debian should have an ​port available for the target platform