Enhancing RTL Synthesis with Incremental Synthesis Techniques

As an RTL Synthesis engineer in the integrated circuit (IC) industry, leveraging Incremental Synthesis is crucial for optimizing design iterations and achieving efficient performance. This blog explores advanced Incremental Synthesis techniques, highlighting specific case studies and the latest cutting-edge technologies in digital design.

The Role of Incremental Synthesis​

Incremental Synthesis focuses on re-synthesizing only the portions of the design that have changed, rather than the entire design. This approach significantly reduces synthesis runtime, making it particularly beneficial for large designs or iterative design processes.

Key Techniques in Incremental Synthesis​

1. Selective Re-synthesis
Selective re-synthesis involves identifying and re-synthesizing only the modified parts of a design, ensuring that the rest of the design remains intact. This technique enhances efficiency and maintains the stability of the unmodified sections.

Case Study:
A design team used Synopsys' Design Compiler for selective re-synthesis. By focusing on the changes, they achieved a 6x reduction in runtime compared to full synthesis. This approach was particularly effective for large-scale FPGA designs, allowing for quicker iterations and improved overall productivity.

Implementation:
Change Detection:Use tools that can detect changes at the RTL level and isolate the affected areas.
Incremental Compilation:Apply incremental compilation techniques to re-synthesize only the modified portions.

2. Hierarchical Incremental Synthesis
Hierarchical Incremental Synthesis divides the design into smaller, manageable blocks. Each block can be synthesized independently, and only the modified blocks are re-synthesized during subsequent iterations.

Case Study:
A network processor design team adopted hierarchical incremental synthesis using Synopsys tools. By partitioning their design and synthesizing individual blocks, they managed to maintain high performance and accuracy while reducing synthesis runtime and complexity.

Implementation:
Design Partitioning:Divide the design into hierarchical blocks to facilitate independent synthesis.
Block-Level Synthesis:Synthesize each block separately and integrate them to ensure consistency.

Advanced Approaches in Incremental Synthesis​

1. Physically Aware Incremental Synthesis
Physically Aware Incremental Synthesis incorporates physical design information into the synthesis process. This approach ensures that the synthesized netlist is optimized for placement and routing, reducing iterations between synthesis and physical design.

Case Study:
A semiconductor company used Mentor Graphics' Precision RTL Plus for physically aware incremental synthesis. This tool enabled them to achieve better timing closure and reduce physical design iterations by incorporating placement and routing information early in the synthesis process.

Implementation:
Physical Constraints Integration: Integrate physical constraints into the synthesis process to guide optimization.
Placement-Aware Tools: Utilize tools that support physically aware synthesis for better timing and congestion management.

2. Power-Aware Incremental Synthesis
Power-Aware Incremental Synthesis optimizes the design for power consumption by incorporating power constraints during the synthesis process. This approach is essential for low-power and battery-operated applications.

Case Study:
A mobile processor design team used power-aware incremental synthesis to optimize their design for low power. By focusing on power constraints early in the synthesis process, they achieved significant reductions in dynamic and static power, enhancing the battery life of their devices.

Implementation:
Power Constraints: Define power constraints early in the design process to guide synthesis.
Low-Power Techniques: Implement low-power techniques such as clock gating and multi-threshold voltage cells.