FPGA Based System Design

1. FPGA Based System Design Tahir Muhammad tm.uettaxila@yahoo.com Spring 2013 Lecture 1

2. Course Organization • Course material: • All the course material can be found at the course webpage • http://web.uettaxila.edu.pk/CMS/SP2013/ectFPBbs/index.asp • Instructor: Tahir Muhammad Office: ASIC Lab, UET Taxila Email: tm.uettaxila@yahoo.com Office Hours: Wednesday

3. Course Objectives 
After taking this course, you will: • Learn how to design digitalcircuits with HDL • Have an understanding • VLSI: Fabrication, circuits, interconnects • FPGA based design techniques • FPGA fabrics • FPGA optimization for size, speed, and power consumption • Verilog HDL • The structure of large digital circuits • Large scale platform and multi-FPGA systems • Understand some of the important ideas for designing more complex systems.

4. Course Organization • Lectures • Wednesday 5-7 • Labs • Wednesday 1-3 • Textbook • FPGA-Based System Design by Wayne Wolf We will mark which section in the book corresponds to the material covered in each lecture Lecture notes are often enough to do the homeworks and the exams, but reading the book is highly recommended

5. Course Outline • Chapter 1: FPGA Based Systems • Chapter 2: VLSI Technology • Chapter 3: FPGA Fabrics • Chapter 4: Combinational Logic • Chapter 5: Sequential Machines • Chapter 6: Architectures • Chapter 7: Large Scale Systems

6. Overview • Why VLSI? • Moore’s Law. • Why FPGAs? • The VLSI and system design process.

7. Why VLSI? • Integration improves the design: • lower parasitics = higher speed; • lower power; • physically smaller. • Integration reduces manufacturing cost-(almost) no manual assembly.

8. VLSI and you • Microprocessors: • personal computers; • microcontrollers. • DRAM/SRAM/flash. • Audio/video and other consumer systems. • Telecommunications.

9. Moore’s Law • Gordon Moore: co-founder of Intel. • Predicted that number of transistors per chip would grow exponentially (double every 18 months). • Exponential improvement in technology is a natural trend: steam engines, dynamos, automobiles.

10. Moore’s Law plot

11. The cost of fabrication • Current cost: $2-3 billion. • Typical fab line occupies about 1 city block, employs a few hundred people. • New fabrication processes require 6-8 month turnaround. • Most profitable period is first 18 months-2 years.

12. Cost factors in ICs • For large-volume ICs: • packaging is largest cost; • testing is second-largest cost. • For low-volume ICs, design costs may swamp all manufacturing costs. • $10 million-$20 million.

13. Mask cost vs. line width

14. Field-programmable gate arrays • FPGAs are programmable logic devices: • Logic elements + interconnect. • Provide multi-level logic. LE Interconnect network LE LE LE LE LE

15. FPGAs and VLSI • FPGAs are standard parts: • Pre-manufactured. • Don’t worry (much) about physical design. • Custom silicon: • Tailored to your application. • Generally lower power consumption.

16. Standard parts vs. custom • Do you build your system with an FPGA or with custom silicon? • FPGAs have shorter design cycle. • FPGAs have no manufacturing delay. • FPGAs reduce inventory. • FPGAs are slower, larger, more power-hungry.

17. Challenges in system design • Multiple levels of abstraction: logic to CPUs. • Multiple and conflicting constraints: low cost and high performance are often at odds. • Short design time: Late products are often irrelevant.

18. FPGA-based system design The system design process • May be part of larger product design. • Major levels of abstraction: • specification; • architecture; • logic design; • circuit design; • layout.

19. Dealing with complexity • Divide-and-conquer: limit the number of components you deal with at any one time. • Group several components into larger components: • transistors form gates; • gates form functional units; • functional units form processing elements; • etc.

20. Hierarchical name • Interior view of a component: • components and wires that make it up. • Exterior view of a component = type: • body; • pins. cout Full adder sum a b cin

21. Add2.a Add1.a Instantiating component types • Each instance has its own name: • add1 (type full adder) • add2 (type full adder). • Each instance is a separate copy of the type: cout Add2(Full adder) Add1(Full adder) sum sum a a b b cin cin

22. A hierarchical logic design box1 box2 x z

23. Net list: net1: top.in1 in1.in net2: i1.out xxx.B topin1: top.n1 xxx.xin1 topin2: top.n2 xxx.xin2 botin1: top.n3 xxx.xin3 net3: xxx.out i2.in outnet: i2.out top.out Component list: top: in1=net1 n1=topin1 n2=topin2 n3=topine out=outnet i1: in=net1 out=net2 xxx: xin1=topin1 xin2=topin2 xin3=botin1 B=net2 out=net3 i2: in=net3 out=outnet Net lists and component lists

24. Component hierarchy top i1 xxx i2

25. Hierarchical names • Typical hierarchical name: • top/i1.foo component pin

26. Layout and its abstractions • Layout for dynamic latch:

27. Stick diagram

28. Transistor schematic

29. Mixed schematic inverter

30. Levels of abstraction • Specification: function, cost, etc. • Architecture: large blocks. • Logic: gates + registers. • Circuits: transistor sizes for speed, power. • Layout: determines parasitics.

31. Circuit abstraction • Continuous voltages and time:

32. Digital abstraction • Discrete levels, discrete time:

33. Register-transfer abstraction • Abstract components, abstract data types: 0010 + 0001 + 0011 0100

34. Top-down vs. bottom-up design • Top-down design adds functional detail. • Create lower levels of abstraction from upper levels. • Bottom-up design creates abstractions from low-level behavior. • Good design needs both top-down and bottom-up efforts.

35. English Throughput, design time Executable program Function units, clock cycles function Sequential machines cost Literals, logic depth Logic gates nanoseconds transistors microns rectangles Design abstractions specification behavior register- transfer logic circuit layout

36. FPGA design • FPGA manufacturer creates an FPGA fabric; system designer uses the fabric. • FPGA fabric design issues: • Study sample user designs. • Select interconnect topology. • Create logic element structures. • Design circuits, layout.

37. Why do we care about layout? • We won’t design layout. • Layout determines: • Logic delay. • Interconnect delay. • Energy consumption. • We want to understand sources of FPGA characteristics.

38. Design validation • Must check at every step that errors haven’t been introduced-the longer an error remains, the more expensive it becomes to remove it. • Forward checking: compare results of less- and more-abstract stages. • Back annotation: copy performance numbers to earlier stages.