sky130hd/gcd: tighten due to 0 tns

| Metric                                        | Old      | New      | Type     |
| ------                                        | ---      | ---      | ----     |
| detailedroute__route__wirelength              |     9789 |    12001 | Failing  |
| finish__timing__setup__ws                     |    -0.03 |    -0.76 | Failing  |
| finish__design__instance__area                |     3685 |     5000 | Failing  |
| finish__timing__drv__setup_violation_count    |       20 |       30 | Failing  |
| finish__timing__wns_percent_delay             |    -10.0 |   -39.08 | Failing  |

Signed-off-by: Matt Liberty <[email protected]>

Author: maliberty

flow/designs/sky130hd/gcd/constraint.sdc

@@ -2,7 +2,7 @@ current_design gcd
 
 set clk_name  core_clock
 set clk_port_name clk
-set clk_period 3.4
+set clk_period 2.5
 set clk_io_pct 0.2
 
 set clk_port [get_ports $clk_port_name]