How Does Marvell Improve Productivity and TapeOut Time with Automated ECO Implementation?

In the chip developmental process, bugs are prone to occur, and there is an exponential rise in bug-fixing costs as it advances the design stages. In the past, bugs like Pentium FDIV have led to catastrophes. So, it is highly desirable to find and fix these bugs before tapeout to ensure no functionality is compromised in a chip. Most such fixes are addressed via engineering change orders (ECOs). Typically, every project has multiple ECOs late in the design cycle. It is hard to implement these ECOs manually as manual implementation impacts productivity and time to market (TTM). So, ECOs after RTL freeze must be automated to avoid any such challenges.

Marvell Technologies faced similar challenges, as mentioned in the recent CadenceLIVE Silicon Valley 2022 paper by Deekshith Krishnegowda from Marvell. He spoke about how Conformal ECO Designer adoption helped them to automate their pre-mask ECOs implementation and complete it in 645 –730sec only.

Key Features That Led Marvell To Adopt the Conformal ECO Designer: The Motivation

Design teams at Marvell noticed that manually performing ECO was close to impossible. With an automated flow, Marvell could complete complex ECO changes while avoiding human error. Another challenge for the Marvell design team was reducing the tape-out time and using both Conformal ECO and Conformal Logical Equivalence Checking (LEC) flows to help minimize the overall tape-out time. In addition, Conformal ECO offers other benefits that Led Marvell to it.

• Existing formal verification flow can be leveraged with minimal changes for Conformal ECO flow.
• Improve productivity by reducing the time taken in the ECO phase.
• Enables both pre-mask and post-mask automated ECOs  

Conformal ECO Flow As Used by Marvell

Marvell has performed multiple ECOs using Conformal’s automated flow on various projects over the past few years. The figure below shows their current Conformal ECO flow:

• R1 = RTL1, Original design without ECO
• G1 = SYN1 or LAY1, Synthesis output from RTL1, without ECO
• R2 = RTL2, Modified design with ECO
• G2 = SYN2 – Synthesis output from RTL2 with ECO
• G3 = LAY1 + ECO- -Post routed Netlist with ECO Patch

Below are the steps as followed by Marvell for ECOs automation. Here step 1,2&3 are required to be performed before starting the Conformal ECO flow, and step 4, 5, and 6 are the core of the Conformal ECO flow:

1. R1 Vs. R2 – To ensure the changes in RTL 2 are as intended, LEC golden RTL (R1)  is compared with the modified RTL (R2). The non-equivalence points are reviewed and should be the desired ECOs.
2. R1 vs. LAY1 – LEC golden RTL  (R1) and Layout 1 are compared to ensure these are equivalent
3. R2 vs. SYN2 - New RTL with ECO fix compared with synthesized netlist of R2 for equivalence.
4. LAY1 vs. SYN2 - Non-equivalence expected. This should be similar to the non-equivalence as in step 1, and then ECO is generated.
5. Generate ECO - Analyze the ECO step to generate the patch. Apply the patch to LAY1.
6. LAY1+patch vs. R2 / SYN2 – This should be equivalent to ensuring the ECO is successfully applied.

Use-Case and Results

Marvell presented results on various use cases involving combinatorial changes, including:  

1. Pre-mask ECO was done using Conformal ECO to fix a register (200k size) read-back issue. ECO involved a change in the combinatorial logic of a ternary operator at two places.
2. Pre-mask ECO was done to fix a write logic to a 16-bit register (same as above). The address decoding of the register had a faulty connection.

Both the cases were in the same logic block with the same size, the ECO fixes, and summary of ECO changes is as below:

Conclusion

Implementing design changes is challenging and may lead to tape-out delays, especially with combinatorial circuits. Conformal ECO automates the process and improves productivity by reducing the time taken in the ECO phase. Adopting Conformal ECO Designer at Marvell helped the design team quickly and accurately complete pre-mask ECOs. Conformal can handle complicated ECOs involving combinational and sequential logic changes with ease. In the case of sequential logic ECOs, Conformal seamlessly handles all DFT and scan chain-related challenges.

Learn More

There are a lot of training materials and rapid adoption kits (RAKs) which can be downloaded from Cadence support. Additionally, please refer to the below topics to learn more about Conformal ECO:

• Conformal ECO Designer
• Genus Synthesis Solution
• Innovus Implementation System