I have a robotics project that is using up all of the UARTs on our low level controller, which is powered by a Teensy 3.5 ... The actuators typically use a wired remote control where the motor is the master and it requires a well-timed response over RS-485 from the remote. We've hacked the remote so that we can use the Teensy for motion control (and were lucky enough to finagle the proprietary protocol through signing of DND).. So I was thinking I'd use Arduino's serialEvent() library to detect the particular message we're looking for, but it doesn't look like the library is going to be useful for anything above Serial3... well, one of my motors is on Serial4.

Is there any simple way to attach the Serial4.available() flag to an ISR or something like that?