Real-time operating via Python

Question

So I am an inexperienced Python coder, with what I have gathered might be a rather complicated need. I am a cognitive scientist and I need precise stimulus display and butto

Answer 1

Most common operating systems' interrupts are variable enough to ruin timing in your experiment regardless of your programming language. Python adds it's own unreliability. Windows interrupts are especially bad. In Windows, most interrupts are serviced in about 4 milliseconds, but occasionally an interrupts last longer than 35 milliseconds! (Windows 7).

I would recommend trying the PsycoPy application to see if will work for you. It approaches the problem by trying to make the graphics card do the work in openGL, however some of it's code still runs outside the graphics card and is subject to the operating system's interrupts. Your existing python code may not be compatible with PsycoPy, but at least you would stay in Python. PsycoPy is especially good at showing visual stimulations without timing issues. See this page in their documentation to see how you would handle a button press: http://www.psychopy.org/api/event.html

To solve your problem the right way, you need a real-time operating system, such as LinuxRT or QNX. You could try your python application in one of those to see if running python in a real-time environment is good enough, but even python introduces variability. If python decides to garbage collect, you will have a glitch. Python itself isn't real time.

National Instruments sells a setup that allows you to program in real-time in a very easy-to-use programming language called LabviewRT. LabviewRT pushing your code into an FPGA daughter card that operates in real time. It's expensive.

I strongly suggest you don't just minimize this problem, but solve it, otherwise, your reviewers will be uncomfortable.