With a continuously running clock do one pull-up the first minute, two pull-ups the second minute, three pull-ups the third minute... continuing as long as you are able. Use as many sets each minute as needed.
Pay no mind to the short reps from the pull ups closest!
Set up before a clock, and every minute on the minute perform 5 pull-ups, 10 push-ups, and 15 squats.
If you fall behind the clock keep going for thirty minutes and see how many rounds you can complete.
If you've finished the workout before this time add +1 to each exercise, i.e., 6 pull-ups, 11 push-ups, and 16 squats each minute, and see if you can go the full thirty minutes.