**Routing** in the context of **Place and Route (PnR)** refers to the process of establishing electrical connections between the various components placed on a chip after the placement stage. This step is crucial in the physical design flow of integrated circuits, including System on Chips (SoCs). Here's a detailed overview of routing:
### Key Objectives of Routing
1. **Establish Connections**:
- Connect pins of different components (gates, flip-flops, etc.) according to the netlist generated during synthesis, ensuring that all specified connections are made.
2. **Minimize Wire Length**:
- Reduce the total length of routing paths to improve signal integrity and minimize parasitic capacitance, which can affect performance.
3. **Avoid Congestion**:
- Ensure that routing paths do not create bottlenecks where too many signals converge, which can lead to delays and increased capacitance.
4. **Maintain Signal Integrity**:
- Design the routing to avoid crosstalk and interference between adjacent wires, ensuring that signals maintain their integrity during operation.
5. **Adhere to Design Rules**:
- Comply with manufacturing design rules, including spacing between wires, widths, and layer usage to ensure manufacturability and reliability.
### Steps in the Routing Process
1. **Global Routing**:
- An initial pass that defines the general paths that the signals will take across the chip without focusing on the precise details. It allocates routing resources to various signals based on their connectivity requirements.
2. **Detailed Routing**:
- A more precise routing phase that specifies the exact paths for each signal. This includes selecting specific layers of metal for routing and ensuring that all design rules are satisfied.
3. **Multi-layer Routing**:
- Utilization of multiple metal layers (typically 4-8 or more) to manage signal connections efficiently. Different layers can be used for different types of signals, reducing congestion.
4. **Wire Optimization**:
- After the initial routing, additional optimizations may be performed to minimize delay and power consumption, such as adjusting wire widths or paths.
5. **Final Checks**:
- Conducting checks to ensure that all connections are made correctly, and performing design rule checks (DRC) to confirm that the routing adheres to the foundry’s specifications.
### Tools Used in Routing
Common Electronic Design Automation (EDA) tools for routing include:
- **Cadence Innovus**
- **Synopsys IC Compiler**
- **Mentor Graphics Olympus-SoC**
### Importance of Routing
- **Functional Correctness**: Proper routing is essential for ensuring that the final design functions as intended, as it connects all the components according to the design specifications.
- **Performance Optimization**: Effective routing can significantly impact the overall performance of the chip, affecting speed and power consumption.
- **Manufacturability**: Adhering to design rules and producing a clean routing layout ensures that the chip can be manufactured reliably.
In summary, routing in Place and Route (PnR) is a critical step in SoC design that establishes the connections between various components, focusing on performance, manufacturability, and adherence to design rules while ensuring functional correctness.
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