Automatic Full-Layers Functional ECO Flow

Overview

Full layers functional ECO can add or delete gates freely. The ECO operations are done in a GofCall script which is compatible with Perl, and it uses exported APIs to access, modify and save the netlist database. GOF reads in two netlist files, Implementation Netlist which is under ECO and Reference Netlist which is re-synthesized from modified RTL with the same constraints as the pre-layout netlist. In the GofCall script, the API 'fix_design' is used to fix the top level module and its sub-modules in global mode. GOF uses the built-in Logic Equivalent Check Engine to figure out the non-equivalent points. And optimized minimum size gate patches are applied to fix the non-equivalent modules.

As shown in the Figure 1, two logic cones are extracted from the Implementation and Reference Netlist for the same compare point. The implementation point mismatches the reference point initially. GOF compares the two points and generated a patch from Reference logic cone and applies to Implementation Netlist. After the patching, the two points become equivalent.

Figure 1: Logic Cone Optimization

GOF does logic cone analysis and optimization for each failing point found in top down logic equivalence check. The failing point is in format of output port or sequential element’s input pin, such as flop’s D input. The final patch has the minimum number of gates to make the implementation logic cone equal to the reference logic cone.

The flow chart is shown in the Figure 2.

Figure 2: Automatic functional ECO flow

Files and data requirements

• Liberty files with extension '.lib'
• Other Verilog libraries files for modules not covered in '.lib' files
• Implementation Netlist on which ECO will be done
• Reference Netlist synthesized with the same constraints as the pre-layout netlist
• The top level module name under ECO

Steps to do automatic functional ECO

Steps for an automatic functional ECO:

• Modify the original RTL
• Synthesize the new RTL to get Reference Netlist
• Create GofCall ECO script:
  • Specify ECO name in 'setup_eco'
  • Load Liberty files and Verilog libraries
  • Load Reference Netlist and Implementation Netlist
  • Fix the design by 'fix_design'
  • Report ECO status and write out ECO results
• Run the above ECO script

Automatic Functional ECO example script

The GofCall script has exact the same syntax of Perl script. It runs the exported APIs that access the netlist database and modify the netlist.

The following is the example script for automatic functional ECO:

# GofCall ECO script, run_example.pl
use strict;
undo_eco; # Discard previous ECO operations
setup_eco("eco_example");# Setup ECO name
read_library("art.5nm.lib");# Read in standard library
read_design("-ref", "reference.gv");# Read in Reference Netlist
read_design("-imp", "implementation.gv");# Read in Implementation Netlist Which is under ECO
set_top("topmod");# Set the top module
# Preserve DFT Test Logic
set_ignore_output("scan_out*");
set_pin_constant("scan_enable", 0);
set_pin_constant("scan_mode", 0);
fix_design;
save_session("current_eco_name"); # Save a session for future restoration
report_eco(); # ECO report
check_design("-eco");# Check if the ECO causes any issue, like floating
write_verilog("eco_verilog.v");# Write out ECO result in Verilog
exit; # Exit when the ECO is done, comment it out to go to interactive mode when 'GOF >' appears

Run and debug

The GofCall Script can be run by '-run' option.

Check Run and debug GofCall script section in User Manual for more detail

An example in released package

The example is in the released package.

To run the example:

The log file shows there are total 35 gates in the initial logic cone. After optimization, the patch has only 1 complex cell and 8 inverts