Simulink in external mode with Arduino - Stops at 2%

Hello.

When I running a model in Simulink with Arduino blocks in external mode - it stops at 2%. Some Times it more that 2%.

I'm sending both through RX and TX at the same time.

Is that the problem or is it a bug?

I'm sending every 500uS from the computer to the Arduino Mega 2560. And i receive every 1mS from the Arduino to the computer.

I'm using Linux Mint and i have Matlab 2016B.

Isin't there a way to run a model in half external mode? The 500uS signal is only from a pulse generator block. The pulse generator drivning a digital output only.

I only want to receive analog values every 1mS.