Mcline,
If you look in vsg_example_complex_freq_hopping, you’ll see vsgSubmitIQ(). You could output a trigger pulse by adding vsgSubmitTrigger(). The API sends them to the VSG in the order received. So if you Submit some I/Q data, then submit trigger and then more I/Q data, the trigger’s rising edge will match the first sample of second chunk of I/Q data.