Realtime CPP standalone

[victorbenichoux]

Hi guys,

Lately I have been playing around with the CPP standalone device in realtime.
The way I do this is pretty close from what we used to do in brian1, that is tell brian to wait untill it is on par with real time. So, in Network::run, I added this at the beginning of the main loop:

#if REALTIME
      rel_time = std::clock()/(double)CLOCKS_PER_SEC - t_start;
      //      std::cout << "real time: " << rel_time << std::endl;
      //      std::cout << "brian time: " << clock->t_() << std::endl;
      if  (rel_time > clock->t_()){
        std::cout << "running late: " << rel_time << std::endl;     
      }
      while (rel_time < clock->t_()){
        rel_time = std::clock()/(double)CLOCKS_PER_SEC - t_start;
      }
#endif

This works fine (appart from what seem to be rounding errors), and I feel that using the #if syntax is appropriate in this context.
Now, if I want fiddle around with the brian script and re-generate code, I have to redo this modification everytime, its a pain.

I am thinking that this is a straightforward enough change (and somewhat useful feature) to be included in brian2. But to do this cleanly, I have to figure out a way to modify a #define REALTIME (0)statement at the top of network.cpp, and as far as I understand, the contents of brianlibare static (as in not code generated).

So, my question is, do you see an easy way to set a #define REALTIME (1) conditionally on, say, a brian_prefs.codegen.realtime = True?
I can upload my realtime brian2 branch if you want to have a look at the modified network.cpp.

To satisfy you curiosity, the reason why I do this is that with CPP standalone, I can run 128 gammatone channels in realtime with my laptop. Therefore I'm currently trying to make a complete sound input > gammatone > realtime plotting with Qt chain. Part of this requires some sort of realtime brian2. Any other ideas or remarks about this are welcome!

[thesamovar]

That's really cool that you're using standalone for that. A couple of comments.

Firstly, your strategy is nice but only works if you are running at faster than realtime. We were also considering that you could do things like increasing dt if you were running too slow, but maybe that's not an issue for you.

Secondly, you should be able to do what you're aiming at already without changing the core of Brian. The trick is to use the insert_code function which basically lets you insert a string directly into the main.cpp file, so in your case you'd do something like:

insert_code('''
#ifdef REALTIME
...
''')
run(...)
insert_code(''''
#endif
''')

Could you give that a try and see if it does everything you need?