Skip writing the updated_clk.sdc if there is no constrained path

Fixes #751

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

Author: maliberty

flow/scripts/write_ref_sdc.tcl

@@ -15,19 +15,23 @@ if { [llength $clks] == 0 } {
 
   if { [llength $clks] == 1 } {
     set slack [sta::time_sta_ui [sta::worst_slack_cmd "max"]]
-    set ref_period [expr ($period - $slack) * (1.0 - $margin/100.0)]
-    utl::info "FLW" 8 "Clock $clk_name period [format %.3f $ref_period]"
-    utl::info "FLW" 9 "Clock $clk_name slack [format %.3f $slack]"
-
-    set sources [$clk sources]
-    # Redefine clock with updated period.
-    create_clock -name $clk_name -period $ref_period $sources
-    # Undo the set_propagated_clock so SDC at beginning of flow uses ideal clocks.
-    unset_propagated_clock [all_clocks]
-    write_sdc [file join $env(RESULTS_DIR) "updated_clks.sdc"]
-    # Reset
-    create_clock -name $clk_name -period $period $sources
-    set_propagated_clock [all_clocks]
+    if { $slack < 1e30 } {
+      set ref_period [expr ($period - $slack) * (1.0 - $margin/100.0)]
+      utl::info "FLW" 8 "Clock $clk_name period [format %.3f $ref_period]"
+      utl::info "FLW" 9 "Clock $clk_name slack [format %.3f $slack]"
+  
+      set sources [$clk sources]
+      # Redefine clock with updated period.
+      create_clock -name $clk_name -period $ref_period $sources
+      # Undo the set_propagated_clock so SDC at beginning of flow uses ideal clocks.
+      unset_propagated_clock [all_clocks]
+      write_sdc [file join $env(RESULTS_DIR) "updated_clks.sdc"]
+      # Reset
+      create_clock -name $clk_name -period $period $sources
+      set_propagated_clock [all_clocks]
+    } else {
+      utl::warn "FLW" 13 "No constrained path found. Skipping sdc update."
+    }
   } else {
     utl::warn "FLW" 10 "more than one clock found. Skipping sdc update."
   }