NanDigits Design Automation

Matching nets from RTL to Netlist

One challenge of an ECO is to find the right spot in a netlist to match the modified code in RTL. If the modified code is on inputs, outputs and flops, things become easy, since they are usually preserved during synthesis. But wires are usually renamed or completely optimized away by synthesis tool. To manually find these wires are very hard and timing consuming or sometime impossible.

GOF has a RTL-to-Netlist Matching feature to easy the process, although it's not 100% to find matched net if it is completely optimized away by synthesis tool. 

To use the feature, you need to load in the submodule GTECH file which will have ECO applied on and the netlist file that contains the submodule.  The GTECH format is Synopsys's generic uncompiled gates. Read in RTL into DC and write it back, you get GTECH format file.

Use following DC commands to get GTECH file.

read -f verilog submodule.v

write -f verilog -hierarchy submodule -o submodule.gtech.gv

Note: GTECH created by DC version 2005 has been fully tested

Load the GTECH file, synthesis library and the netlist file by command line:

gof -v library.v top_netlist.gv -gtech submodule.gtech.gv -synlib synthesis.lib

Note: The old GOF versions needed to setup register pattern,  from version V2.216 GOF has removed this requirement by extracting information from synthesis library instead.

You will get two tree hierarchies in the left side window. Double click the GTECH tree to load the GTECH file into GofViewer. Find the net that needs to be matched to netlist. Click on a net, in this example, 'qcif128oky', right click to pop up menu, select Matching to Netlist item. 

The result window pops up to display the matching process and final result. Depends on Fanin/Fanout missing numbers, the result has been classified to different levels.  It will also show if the function exactly match RTL net. (Highlighted in Red)

Click on the gate listed and highlight it. Right click to pop up menu and select send to Schematic New.

A schematic window pops up to display the gate. And do tracing Fanin/Fanout by mouse middle button clicking on the pins of gates.

You can load GTECH gate to same schematic to do cross check.

The GTECH gate is on the same schematic as the gates from netlist. You can select U360's output and run 'List Fanout Endpoints' function to find out why U360 has 11 fanouts missing. Check List Fanin/out Endpoints for detail.