I need a little hint. I have to write an application for our board which is using EMX. We already have an application which serves as attendance panel - user can choose from list of attendance events, enclose his RFID card, so the event is generated, stored on SD card and send over LAN to our server. It works well without any significant problems.
Now, we have to connect it directly to our control unit (runs Linux) which communicates with devices over RS 485 bus. Problem is that our control unit periodically tests device on the bus if they are responding by sending connection tests. Device has to reply to this connection test in 30 ms, otherwise connection lost with this device is declared by the control unit. I have already managed to write simple communication using SerialPort class in .NETMF which can respond to this packet in 30 ms. But now I need to implement GUI for user interaction and I’m starting to worry that I cannot ensure that I will always respond to connection test in 30 ms. Any hints how can I solve such a time-critical task?