dff_cntr run with dff_cntr.run  just trace counter before clock falls
q3,q2,q1,q0 0000 at time 15 ns
q3,q2,q1,q0 0001 at time 31 ns
q3,q2,q1,q0 0010 at time 47 ns
q3,q2,q1,q0 0011 at time 63 ns
q3,q2,q1,q0 0100 at time 79 ns
q3,q2,q1,q0 0101 at time 95 ns
q3,q2,q1,q0 0110 at time 111 ns
q3,q2,q1,q0 0111 at time 127 ns
q3,q2,q1,q0 1000 at time 143 ns
q3,q2,q1,q0 1001 at time 159 ns
q3,q2,q1,q0 1010 at time 175 ns
q3,q2,q1,q0 1011 at time 191 ns
q3,q2,q1,q0 1100 at time 207 ns
q3,q2,q1,q0 1101 at time 223 ns
q3,q2,q1,q0 1110 at time 239 ns
q3,q2,q1,q0 1111 at time 255 ns
q3,q2,q1,q0 0000 at time 271 ns
q3,q2,q1,q0 0001 at time 287 ns