4-bit fibonacci LFSR. see https://en.wikipedia.org/wiki/Linear_feedback_shift_register
Trigger that will calculate a new value.
Initial seed. Use 8 (2r1000) to get the common sequence: [4, 2, 9, 12, 6, 11, 5, 10, 13, 14, 15, 7, 3, 1, 8]
8 (2r1000)
[4, 2, 9, 12, 6, 11, 5, 10, 13, 14, 15, 7, 3, 1, 8]
Pseudo random numbers 0-15.