For a Subaru, take a look around this site. You may want to read up on the differences in the Subaru Select Monitor (SSM) protocol as opposed to the OBDII protocol. It provides Subaru-specific parameters and can update at a much higher rate than generic OBDII. There is much free software out there for SSM for datalogging and downloading/flashing ROMs, but you need a special cable to use it. So if you want this kind of access to your ecu, then read up on those cables. The OpenPort and the Cobb Accessport cables work very nice.