I have recently purchased an Arduino Nano for use in an automotive project. I will be using it to do some signal conversion for an air flow sensor. The nano will be feeding signals into my ECU. The power to the nano will come from a regulated 5v output from the ECU which also feeds the sensors. This 5v feed comes live when the engine is cranked over for starting. What I need to know is how long the nano will take to boot up and execute my signal conversion code. I am not sure how the ECU will respond if it doesnt see a signal for a short period of time.
It is not boot time but when it powers up a short serial message is sent and an acknowledge is looked for. That is to see if the boot loader is to receive a new program. If that byte does not come in then the existing program starts. That process can take a few seconds (3 to 5) and can feel like a booting process.
If it is unacceptable then you have the choice of bypassing the boot loader if you use an external programmer.