The global variable fps holds the current frames per second on which Bennu is running. This means how many times a frame is executed every second and how many times the screen is updated every second.
If a different FPS is needed, the target FPS can be altered by use of set_fps().
If a more accurate FPS is needed, use frame_time to calculate it.
If you need to view the FPS in-game, please use the code (in a loop): write_int(0,0,0,0,&fps);