ORRAM: An OpenROAD-Integrated RAM Generator Using Standard Cells

2026-07-13

AI Summary

This work addresses a critical bottleneck in traditional ASIC design, where RTL-inferred memories often manifest as dense arrays of flip-flops, degrading performance. While existing memory compilers typically rely on third-party tools or non-standard cells, this paper presents the first PDK-agnostic RAM generator implemented entirely with standard cells within the OpenROAD framework. Requiring only a generic standard-cell library, the proposed approach automatically produces fully placed-and-routed RAM modules without custom bitcells or external dependencies. It supports arbitrary word widths, depths, mask granularities, multiple read ports, column multiplexing, and latch-based architectures, and is validated across industry-standard libraries such as sky130hd and NanGate45. Timing-closure is confirmed via OpenSTA, and on the SkyWater 130nm process, the solution achieves bit density comparable to DFFRAM while offering significantly enhanced functionality. The implementation is open-sourced and integrated into OpenROAD.

Abstract

Memory inference remains a significant challenge in turnkey ASIC design flows. Inferring flip-flops from RTL can create thousands of densely interconnected instances which dramatically slow down design flows and impede performance. Memory compilers address this issue, although they are third-party tools which are often PDK-specific and may require specialized cells not in the base PDK. To address these shortcomings, we present ORRAM, a standard-cell-based memory generator built as a native module within OpenROAD. Given a standard cell library, ORRAM produces a fully placed and routed RAM block requiring no custom bitcells or external tooling, with timing verification via OpenSTA rather than SPICE simulation. ORRAM supports arbitrary word sizes, word counts, mask granularities, multi-port read configurations, column muxing, latch-based storage, and automatic PDK-agnostic cell selection, making it compatible with most standard cell libraries including sky130hd and NanGate45. Evaluated on SkyWater 130nm, ORRAM matches the bit density of historical DFFRAM results while offering a significantly expanded feature set. The source code is available as part of the OpenROAD project.

Problem

• memory inference
• ASIC design flow
• standard cell library
• PDK-specific
• RAM generator

Innovation

• standard-cell-based RAM
• OpenROAD integration
• PDK-agnostic memory generation
• automatic cell selection
• turnkey ASIC flow