1. EE 466/586 VLSI Design Partha Pande School of EECS Washington State University pande@eecs.wsu.edu

2. Lecture 18 Implementation Methods

3. The Design Productivity Challenge Source: sematech97 A growing gap between design complexity and design productivity 1981 Logic Transistors per Chip (K) Productivity (Trans./Staff-Month) 19831985198719891991199319951997199920012003200520072009

4. A Simple Processor MEMORY DATAPATH CONTROL INPUT-OUTPUT INPUT/OUTPUT

5. Simple Processor (Cont’d)  Datapath All computations are performed Combinational & Arithmetic operations  Control Module Sequential circuit FSM  Memory module Data storage  Interconnect Integrating the whole system  I/O circuitry Connects to outside world

6. A System-on-a-Chip: Example Courtesy: Philips

7. Implementation Approach  Flexibility (Programmable design) Reuse of single design for multiple applications Upgrade in the field  Hard-wired Totally fixed at the manufacturing time  Flexibility comes at the cost of higher energy dissipation

8. Impact of Implementation Choices Energy Efficiency (in MOPS/mW) Flexibility (or application scope) 0.1-1 1-10 10-100 100-1000 None Fully flexible Somewhat flexible Hardwired custom Configurable/Parameterizable Domain-specific processor (e.g. DSP) Embedded microprocessor

9. Implementation Choices Custom Standard Cells Compiled Cells Macro Cells Cell-based Pre-diffused (Gate Arrays) Pre-wired (FPGA's) Array-based Semicustom Digital Circuit Implementation Approaches

10. Custom Circuit Design  Performance or Design density is of prime importance Long time to market  Can be justified in limited situations Custom block can be reused many time (e.g. memory blocks) Cost can be amortized over large volumes  Design automation Very critical components are designed manually

11. The Custom Approach Intel 4004 Courtesy Intel

12. Transition to Automation and Regular Structures Intel 4004 (‘71) Intel 8080 Intel 8085 Intel 8286 Intel 8486 Courtesy Intel

13. Cell-based Design  Standardizes the design entry level at the logic gate  Library of logic gates Inverter, AND/NAND, OR/NOR, Flip-flops More complex functions, AOI…..  Design generation Schematic using the cells Higher level description language (VHDL, Verilog)  All cells have identical heights  Widths of the cells may vary  Standard cell design can be combined with other layout methodologies

14. Cell-based Design (or standard cells) Routing channel requirements are reduced by presence of more interconnect Layers Feed Through cells – Connect between cells in different rows without having to route around a complete row

15. Standard Cell — Example [Brodersen92]

16. Standard Cell – The New Generation Cell-structure hidden under interconnect layers

17. Standard Cell - Example 3-input NAND cell (from ST Microelectronics): C = Load capacitance T = input rise/fall time

18. Macrocells  Complex blocks than random logic functions  (Multipliers, DSPs …)  Complex cells – Macro cells Macro cells Hard Macro Soft Macro

19. Hard & Soft Macro  Hard Macro - D esign of a logic function on a chip that specifies how the required logic elements are interconnected and specifies the physical pathways and wiring patterns between the components.  Soft Macro - D esign of a logic function on a chip that specifies how the required logic elements are interconnected,but not the physical wiring pattern.

20. Hard MacroModules 256  32 (or 8192 bit) SRAM Generated by hard-macro module generator

21. “Soft” MacroModules Synopsys DesignCompiler

22. “Intellectual Property” A Protocol Processor for Wireless

23. Semicustom Design Flow HDL Logic Synthesis Floorplanning Placement Routing Tape-out Circuit Extraction Pre-Layout Simulation Post-Layout Simulation Structural Physical Behavioral Design Capture Design Iteration

24. The “Design Closure” Problem Courtesy Synopsys Iterative Removal of Timing Violations (white lines)

25. Integrating Synthesis with Physical Design Physical Synthesis RTL(Timing) Constraints Place-and-Route Optimization Artwork Netlist with Place-and-Route Info Macromodules Fixed netlists