AR# 13920: 12.1 Known Issue - Timing Analyzer - My FROM:TO constraint picks up the wrong paths (TNM)
12.1 Known Issue - Timing Analyzer - My FROM:TO constraint picks up the wrong paths (TNM)
How do the TNM and TNM_NET grouping constraints work? I would like to ignore a path between "flopa" and "flopb," passing through net "netand" using a TIG constraint setup like the one shown below. (I would like to remove the information between the double-dashed lines below from timing analysis with the TIG.)
I am specifying my FROM and TO flip-flops using the TNM_NET grouping constraint.
#PERIOD Constraint NET "clk" TNM_NET = "clk"; TIMESPEC "TS_clk" = PERIOD "clk" 7 ns HIGH 50 %;
#Create Groups NET "neta" TNM_NET = "neta_grp"; NET "netand" TPTHRU = "netand_thru"; NET "netb" TNM_NET = "netb_grp";
#Actual Constraint TIMESPEC "TS_broken_TIG" = FROM "neta_grp" THRU "netand_thru" TO "netb_grp" TIG;
No. If you place both TNM and TNM_NET on a net, they both trace forward and pick up all the flip-flops that are encountered downstream; they do not move backward. In this case, "neta_grp" contained "flopb," and "netb_grp" contained "flopc." The FROM and TO constraints tried to remove the green dashed line, but because the THRU point "netand" did not exist, the FROM:THRU:TO constraint came up empty.
How to fix this
From Timing Analyzer, choose Analyze --> Query TimeGroups: