I found the solution to at least one issue - by default the Arduino code is set to only notify you when 120 characters have arrived (or a preset timeout) - removing this latency has helped a lot to made the communications much more responsive.

Within the Arduino code - after the Serial.begin() - I ...

Thank you for trying it -
My timings are a bit more critical.. Its a frame based protocol - and the Master device only waits a few ms before assuming the device is lost - so I need a quick response and they need to be in Request-Response sequence.

Based on your code - here is some code that shows ...

I need to send/transmit with very lot latency - for a bus protocol to connect to a legacy device (security system) I want to connect to. The protocol cannot be changed.

I need the ESP32 to wait for a message (about 16 bytes) on the UART, process it and send a small packet of data (4 bytes) in ...