The example applications we've seen so far have something in common: after initialization and device registration, they call fusd_run(). This gives up control of the program's flow, turning it over to the FUSD library instead. This worked fine for our simple example programs, but doesn't work in a real program that needs to wait for events other than FUSD callbacks. For this reason, our framework provides another way to activate callbacks that does not require the driver to give up control of its main().