Physical Design Flow Quiz: Placement, Routing, and Floorplanning Quiz

Challenge your understanding of key steps in the physical design flow, including placement, routing, and floorplanning. This quiz covers important concepts and decision points in modern chip layout, helping learners solidify their knowledge of physical design techniques and strategies.

1. Placement Constraints

   What is the main objective of cell placement in the physical design flow of an integrated circuit?

   1. To optimize cell locations for minimal wirelength and timing
   2. To partition memory blocks for hierarchical design
   3. To generate the initial floorplan based on power grids
   4. To create a list of net connections for the design

   Explanation: The primary goal of cell placement is to assign each cell a location such that wirelength, routing congestion, and timing are optimized. While floorplanning determines chip areas and boundaries based on power grids, placement specifically deals with arranging individual cells. Creating a netlist is a step performed earlier in the design flow, and partitioning memory blocks is related to hierarchical design, not direct cell placement.

2. Floorplanning Decisions

   In floorplanning, what is a major factor when determining the locations of input and output ports on a chip?

   1. The size of power rails in the design
   2. The number of via layers in routing
   3. External interface requirements and signal integrity
   4. The sequence of gate-level netlist entries

   Explanation: Port placements are primarily influenced by external interface requirements and the need to maintain good signal integrity. While power rail size affects power distribution, the netlist entry sequence is irrelevant to physical port locations. Routing via layers impact wiring but are not a main consideration for initial port location decisions in floorplanning.

3. Routing Challenges

   During the routing stage of physical design, which issue is most commonly addressed to avoid short circuits between adjacent metal wires?

   1. Buffer insertion for long nets
   2. Cross-section area calculation
   3. Spacing violations
   4. Threshold voltage mismatch

   Explanation: Spacing violations occur when metal wires are too close and risk short-circuiting, so routing tools check minimum spacing rules to prevent this. Threshold voltage mismatch is a device-level concern, not directly related to routing. Cross-section area calculation isn't a common routing constraint, while buffer insertion is mostly used for timing improvement, not for preventing shorts.

4. Congestion Prevention

   If routing congestion is observed in a critical region during placement, which technique can help to alleviate the issue before detailed routing begins?

   1. Reducing power grid mesh density
   2. Increasing clock tree buffers indiscriminately
   3. Spreading standard cells in congested areas
   4. Shortening the chip aspect ratio arbitrarily

   Explanation: By spreading standard cells apart in congested regions, additional space is made for routing resources, easing congestion. Reducing power grid density may harm power integrity, and adding more clock tree buffers can worsen congestion. Changing the chip aspect ratio without analysis may create other layout issues and isn't a targeted solution.

5. Design Rules in Physical Layout

   Which statement best describes a 'design rule check' (DRC) in the context of physical chip layout?

   1. A method to program logic gates at the architectural level
   2. A simulation of chip functional behavior
   3. A process to verify geometric and electrical constraints are not violated
   4. A final timing optimization performed on the netlist

   Explanation: DRC ensures that physical layout meets all geometric and electrical design constraints, checking for minimum widths, spacings, and other parameters. Timing optimization focuses on signal delays—not physical rules. Functional simulation tests logic, not layout constraints. Programming logic gates is related to architectural design, not DRC.