The netlist ECO process in IC design involves navigating modifications across various design stages, each with unique characteristics. Typically, these stages include the Synthesis Netlist (or Pre-layout Netlist), the DFT Netlist, and the Post-layout Netlist. Each stage presents distinct requirements and challenges that necessitate a tailored approach to ECO implementation.

For smaller designs, a full re-synthesis can be applied to all three netlist stages. However, the time-intensive nature of a complete automatic ECO run across large designs necessitates a more efficient strategy. GOF ECO addresses this by focusing its automatic ECO capabilities on the initial Synthesis (Pre-layout) Netlist stage.

The workflow involves the following key steps:

• Automatic ECO on Pre-layout Netlist: GOF ECO performs an automatic analysis and generates an output script based on the differences identified in the Synthesis Netlist. This leverages GOF ECO's intelligent functional ECO capabilities for the foundational design representation.
  

• GOF ECO Output Script Generation: Once the Pre-layout Netlist is fixed, GOF ECO produces a script detailing the necessary modifications.

Script Application to Downstream Netlists: This generated GOF ECO output script is then directly applied to the subsequent DFT Netlist and Post-layout Netlist.

The advantages of this approach are significant:

• Enhanced Speed: Executing the GOF ECO output script is considerably faster than running a full automatic ECO analysis on each individual netlist stage. This drastically reduces the overall ECO turnaround time.

• Simplified DFT Handling: By applying the script, there is often no need to explicitly specify DFT constraints during the fix of the DFT and Post-layout Netlists. The functional changes intended by the ECO are propagated without requiring re-analysis of DFT-specific logic.

Addressing Back-end Optimization:

Occasionally, back-end tools perform significant optimizations on the original instances present in the Pre-layout Netlist. This can lead to discrepancies in instance naming and structure that might hinder the direct application of the GOF ECO output script. To overcome this, GOF Debug's schematic viewing capabilities provide a crucial advantage. Engineers can easily visualize the Pre-layout and Post-layout schematics, pinpoint the renamed or optimized instances, and make necessary adjustments to the GOF ECO output script to ensure accurate application.

Managing Isolation Cells in Post-Layout:

A critical consideration in Post-layout Netlists is the presence of isolation cells, which are typically inserted for power management and are absent in the Pre-layout Netlist. Consequently, the standard GOF ECO output script will not include these isolation cells. Directly applying the script might inadvertently bypass the intended behavior of these cells.

To address this, the latest GOF release introduces the set_check_isolation feature. When enabled, this intelligent functionality within GOF ECO analyzes the wires involved in the ECO script and determines if adjustments are needed to maintain the integrity of the isolation cells in the Post-layout Netlist. This ensures that the ECO modifications are applied while preserving the essential power management structures.

In conclusion, GOF ECO offers a streamlined and efficient approach to the IC ECO process by strategically applying automatically generated scripts to downstream netlist stages. Coupled with the debugging capabilities of GOF Debug and the intelligent isolation cell handling of the latest GOF release, this methodology significantly accelerates ECO execution, simplifies DFT considerations, and ensures the accurate implementation of design changes across the entire IC design flow.