BT HomeHub 5 Type A - Hardware Firewall

This is just a random question;

Though does anyone know of any OS i can Flash to my BT HomeHub 5 Type A to act as a Hardware Firewall?

I want this before my Local Routing.

or shall i just buy a FireBox? or Cisco ISA ?

I need to Monitor SPI, if this is possible with OpenWRT, any guide would be helpful.