Serial echo latency

I am developing a real time application which needs to recieve and respond to messages over a serial port with as low latency as possible (Rabbit 2250).

Through a simple setup of serial port C with interrupt priority 1, and a basic echo routine in the main loop, I’m finding that there is a latency of about 200 microseconds between the Rabbit recieving bytes and echoing them (as mesured by an oscilloscope at this stage).

Are there any (simple) ways to improve this latency?

I need to be able to address up to 32 individual Rabbits with 5 bytes of data and recieve 5 bytes back, or timeout and assume there is not a Rabbit at that position (they are situated on sequentially accessed IR channels), and have to address all 32 in this manner every 10 milliseconds.

Baudrate is not a problem, but the 200 microseconds of latency is.

You may need to consider doing the transmit from within the rx interrupt if the latency is a big issue as the code in the main loop will be subject to latency due to other system interrupt sources such as the system timer etc. This may mean having to bypass the library routines and write directly to the serial port registers.