<repack_design_constraints>
  <pin_constraint pb_type="clb" pin="clk[0]" net="clk0"/>
  <pin_constraint pb_type="clb" pin="clk[1]" net="clk1"/>
  <pin_constraint pb_type="clb" pin="clk[2]" net="OPEN"/>
  <pin_constraint pb_type="clb" pin="clk[3]" net="OPEN"/>
</repack_design_constraints>