Devices

Brian 2 supports generating standalone code for multiple devices. In this mode, running a Brian script generates source code in a project tree for the target device/language. This code can then be compiled and run on the device, and modified if needed. At the moment, the only ‘device’ supported is standalone C++ code. In some cases, the speed gains can be impressive, in particular for smaller networks with complicated spike propagation rules (such as STDP).

C++ standalone

To use the C++ standalone mode, make the following changes to your script:

  1. At the beginning of the script, i.e. after the import statements, add:

    set_device('cpp_standalone')
    
  2. After run(duration) in your script, add:

    device.build(project_dir='output', compile_project=True, run_project=True, debug=False)
    

The build function has several arguments to specify the output directory, whether or not to compile and run the project after creating it (using gcc) and whether or not to compile it with debugging support or not.

Not all features of Brian will work with C++ standalone, in particular Python based network operations and some array based syntax such as S.w[0, :] = ... will not work. If possible, rewrite these using string based syntax and they should work. Also note that since the Python code actually runs as normal, code that does something like this may not behave as you would like:

results = []
for val in vals:
    # set up a network
    run()
    results.append(result)

The current C++ standalone code generation only works for a fixed number of run statements, not with loops. If you need to do loops or other features not supported automatically, you can do so by inspecting the generated C++ source code and modifying it, or by inserting code directly into the main loop as follows:

device.insert_device_code('main.cpp', '''
cout << "Testing direct insertion of code." << endl;
''')

The results of a simulation are saved in the results subdirectory of the generated project directory. The files have odd but clear names (this will be improved in later releases). The format of the saved data is as follows:

  • Arrays are saved as flat binary files which can be loaded with numpy.fromfile('filename', dtype=float).

  • A SpikeMonitor M can be loaded as follows:

    i = fromfile('output/results/_dynamic_array_%s_i' % M.name, dtype=int32)
    t = fromfile('output/results/_dynamic_array_%s_t' % M.name, dtype=float64)
    
  • A StateMonitor M recording variable var can be loaded as follows:

    t = fromfile('output/results/_dynamic_array_%s_t' % M.name, dtype=float64)
    vals = fromfile('output/results/_dynamic_array_%s__recorded_%s' % (M.name, var), dtype=float64)
    vals.shape = (t.size, -1)
    vals = vals.T