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Digital Engineering Laboratory Course Introduction & FPGA Concepts and Design

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  1. Digital Engineering LaboratoryCourse Introduction & FPGA Concepts and Design ECE 554 Department of Electrical and Computer Engineering University of Wisconsin - Madison

  2. Instructors • Professor Mike Schulte, • Office: 4619 Engineering Hall • Office hours: Tuesday, Thursday: 2:30 to 3:30 PM Wednesday: 1:00 to 2:00 PM • Jake Adriaens, • TA for M, W Labs • Office hours are assigned lab hours • Ben Kopp, • TA for T, R Labs • Office hours are assigned lab hours

  3. Course Objectives • Deal with problems and solutions associated with many aspects of a large digital design project • Work effectively as a member of a moderate-sized team • Use contemporary commercial design tools, • Use programmable user-defined devices (FPGAs) for rapid prototyping • Learn to get by on very little sleep .

  4. Prerequisites and Location • ECE 351 – Digital Logic Laboratory • ECE/CS 552 – Introduction to Computer Architecture • ECE 551 - Digital System Design and Synthesis (strongly recommended) • Laboratory: 3628 Engineering Hall • Lecture: 3444 Engineering Hall • Lectures, Reviews, and Group Meetings During Lab Hours: 2534 EH (MW) and 3418 EH (TR)

  5. Course Overview Grading • 15% Miniproject – due 2/6 and 2/7 • Design a Special Purpose Asynchronous Receiver/Transmitter (team of 2) • 20% Midterm Bench Exam – on 3/1 and 3/2 • Designed to test your understanding of Design Specifications, Verilog, Debugging, Lab Environment, etc. (individual) • 65% Project – demos 5/1, 5/2, reports 5/10 • Design, implement, test, and program a general or special purpose digital computer that emphasizes some particular features (team of 6, 7)

  6. Online Resources • The course website is at: • Additional course information is at: and at

  7. Miniproject • For the miniproject, you will • Design a Special Purpose Asynchronous Receiver/Transmitter (SPART) and its testbench in Verilog/VHDL • Simulate the design to ensure correct performance • Download the design and associated files and demonstrate correct functionality • Preparing a report on your design •

  8. Midterm Bench Exam • You will be given a specification for a small system along with Verilog code for some pre-designed modules for the system. • You will be expected to: • Understand the specification • Understand the Verilog code provided • Write one or more Verilog modules • Debug one or more Verilog modules • Simulate one or more modules and the entire system • Synthesize and implement the design • Download, test, and demonstrate the design on the FPGA board

  9. Project • Design, simulate, synthesize, test, download and demonstrate a non-trivial computer with an original instruction set architecture (ISA) • Four key requirements • It must be an original ISA (somewhat negotiable) • It must be non-trivial • It must be tractable - everything takes at least twice as long as you expect • It must interface through the serial port with the terminal emulator on the lab workstations (negotiable) • Often has significant software component and utilizes XSV800 FPGA board interfaces • Several major milestones •

  10. FPGA Concepts and Design • CMOS IC design alternatives • RAM cell-based FPGA uses • The Xilinx Virtex Series FPGA technology • The Xilinx Foundation 3.1i design process

  11. CMOS IC Design Alternatives • Field Programmable Gate Array (FPGA) – a hardware device with programmable logic, routing, memory, and I/O STANDARD IC ASIC FIELD PROGRAM- MABLE FULL CUSTOM SEMI- CUSTOM STANDARD CELL GATE ARRAY, SEA OF GATES FPGA CPLD

  12. RAM Cell-Based FPGA Uses • Prototyping gate array, standard cell, or full custom integrated circuits (ICs) • Prototyping complete systems • Implementing “hardware simulation” • Replacing ICs • Providing multifunction reconfigurable system ICs • Hardware accelerators

  13. Xilinx Virtex FPGA Architecture • Primary Reference: • On-Line Xilinx Data Sheet DS003 (v.2.5, April 2, 2001) - • Figure 1: Virtex Architecture Overview • IOBs - Input/Output Blocks • CLBs - Configurable Logic Blocks • Function generators, Flip-Flops, Combinational Logic, and Fast Carry Logic • GRM - General Routing Matrix • 3-State Buffers • BRAMs - Block SelectRAM (configurable memory) • DLLs - Delay-Locked Loops for clock control • VersaRing - I/O interface routing resources

  14. Figure 1- Virtex Architecture Overview

  15. Virtex FPGA Architecture • Logic configured by values stored in SRAM cells • CLBs implement logic in SRAM-stored truth tables • CLBs also use SRAM-controlled multiplexers • Routing uses “pass” transistors for making/breaking connections between wire segments • Block RAMs allow programmable memories with configurable sizes (1, 2, 4, 8, or 16 bits)

  16. Table 1 – Virtex FPGA Family Members • We are using the XCV800 device • 0.22 micron, five-layer metal process

  17. IOB - Input/Output Block • See Figure 2: Virtex Input/Output Block • Separate signals for input (I), output (O), and output enable (T) • Three storage elements function as D flip-flops or latches with clock enable (CE) and set/reset (SR) • I/O pins can connect directly to internal logic or through the storage element • Programmable input delay • 3-state output buffer • I/O pad can use pull-up, pull-down, or weak keeper • Supports a wide range of voltages

  18. Figure 2: Virtex Input/Output Block

  19. CLB - Configurable Logic Block • See Figure 4: 2-Slice Virtex CLB • Each slice contains two logic cells (LCs) and consists of • 2 4-input look-up tables (LUTs) • 2 D flip-flops/latches • Fast carry and control logic • Three-state drivers • SRAM control logic

  20. Figure 4: 2-Slice Virtex CLB

  21. CLB - Configurable Logic Block • See Figure 5: Detailed View of Virtex Slice • Logic Function Implementation • 2 Function Generators - Each a 4-input LUT - implements any 4-input function • F5 multiplexer - combines two LUTs with select input - implements any 5-input function, 4-to-1 mux, or selected functions of up to 9 inputs. • F6 multiplexer - combines outputs of two F5 multiplexer - implements any 6-input function, 8-to-1 mux, or selected functions of up to 19 inputs. • Four direct feedthrough paths - useful to facilitate routing by use of through-the-cell paths

  22. Figure 5: Detailed View of Virtex Slice

  23. CLB - Configurable Logic Block • Storage Elements • 2 D flip-flops/latches • Optionally included in cell output paths • Shared clock enable • Shared synchronous/asynchronous Set/Reset signals • SR - forces storage element into initialization state specified (0 or 1) • BY - forces storage element into opposite state

  24. CLB - Configurable Logic Block • Fast Carry Logic (See Figure 5) • Two chains of two bits per CLB • AND gate, 0/1 Mux, CY Mux, EXOR • 3-state Drivers (BUFT) - on-chip drivers with independent control and input pins • Distributed LUT SelectRAMs – one per logic cell, 2 LUTs can be reconfigured as one of: • Two 16 x 1-bit synchronous RAM • 16 x 2-bit synchronous RAM • 32 x 1-bit synchronous RAM • 16 x 1 dual-port synchronous RAM • Two 16-bit shift registers

  25. Block SelectRAM • Fully synchronous dual-ported 4096-bit RAM • Stores address, data and write-control signal on inputs at clock edge • Cannot change address, even for read without using clock • For dual port use, interesting timing restrictions • Independent control signals for each port • Organized in vertical columns of blocks on left and right of CLB array • Block height is 4 CLBs => Number of block RAMs per column is (height of CLB of array)/4 • See Tables 3 & 4 and Figure 6.

  26. Tables 3 & 4 and Figure 6

  27. Programmable Routing Matrix • Local Routing • See Figure 7: Virtex Local Routing • Interconnections among LUTs, flip-flops, and General Routing Matrix (GRM) • Internal CLB feedback paths that can chain LUTs together • Direct paths between horizontally-adjacent CLBs • Short connections with few “pass” transistors => low delay => high-speed connections • Mix of hardware and software is used to try to minimize routing delay

  28. Figure 7: Virtex Local Routing

  29. Programmable Routing Matrix • I/O Routing • VersaRing • Supports pin-swapping and pin-locking • Facilitates pin-out flexibility for concurrent connecting component design • Dedicated Routing (not programmable) • Four partitionable bus lines per CLB row driven by BUFTs (See Figure 8: BUFT Connections) • Two dedicated nets per CLB for vertical carry signals to adjacent cells

  30. Figure 8: BUFT Connections

  31. Clock Distribution • Via primary global routing resources • See Figure 9: Global Clock Distribution Network • Four global buffers • Two at top center • Two at bottom center • Four dedicated clock input pads • Input to global buffers from pads or from general purpose routing

  32. Figure 9: Global Clock Distribution Network

  33. Delay-Locked Loops (DLLs) • One associated with each clock buffer • Eliminate skew between clock input pad and internal clock-input pins within the device • Each can drive two global clock networks • Clock edges reach internal flip-flops 1 to 4 clock periods after they arrive at the input. • Provides control of multiple clock domains • Has minimum clock frequency restrictions!

  34. Table 1 and Figures 4 & 7

  35. Configuration • How is the FPGA configured? • Implemented by • Clearing configuration memory • Loading configuration data into 2-D configuration SRAM • Activating logic via a startup process • Configuration Modes • Slave-Serial – FPGA receives bit-serial data (e.g., from PROM) synchronized by an external clock • Master-Serial - FPGA receives bit-serial data (e.g., from PROM) synchronized by FPGA clock • SelectMAP - Byte-wide data is written into the FPGA with a BUSY flag from FPGA controlling the flow of data • Boundary-scan – Configuration is done through the Test Access Port • The XCV800 device requires 4,715,616 configuration bits

  36. XCV800 Characteristics • Maximum Gate Count 888,439 • CLB Matrix 56 x 84 • Logic Cells 21,168 • Maximum IOBs 512 • Flip-Flop Count 43,872 • Block RAM Bits 114,688 • Horizontal TBUF Long Lines224 • TBUFs per Long Line 168 • Program Data (bits) 4,715,616

  37. THE ECE 554 XILINX DESIGN PROCESS • Design process overview • Design references • Xilinx libraries • Design tutorial • What’s next

  38. Design Process Steps • Definition of system requirements. • Example: ISA (instruction set architecture) for CPU. • Includes software and hardware interfaces with timing. • May also include cost, speed, reliability and maintainability specifications. • Definition of system architecture. • Example: high-level HDL (hardware description language) representation - this is not required in ECE 554, but is done in the real world). • Useful for system validation and verification and as a basis for lower level design execution and validation or verification.

  39. Design Process Steps(continued) • Refinement of system architecture • In manual design, descent in hierarchy, designing increasingly lower-level components • In synthesized design, transformation of high-level HDL to “synthesizable” register transfer level (RTL) HDL • Logic design or synthesis • In manual or synthesized design, development of logic design in terms of library components • Result is logic level schematic or netlist representation or combinations of both. • Both manual design and synthesis typically involve optimization of cost, area, or delay.

  40. Design Process Steps (Continued) • Implementation • Conversion of the logic design to physical implementation • Involves the processes of: • Mapping of logic to physical elements, • Placing of resulting physical elements, • And routing of interconnections between the elements. • In case of SRAM-based FPGAs, represented by the programming bitstream which generates the physical implementation in the form of CLBs, IOBs, BRAMs, and the interconnections between them

  41. Design Process Steps (continued) • Validation (used at number of steps in the process) • At architecture level - functional simulation of HDL • At RTL level- functional simulation of RTL HDL • At logic design or synthesis - functional simulation of gate-level circuit - not usually done in ECE 554 • At implementation - timing simulation of schematic, netlist or HDL with implemention based timing information (functional simulation can also be useful here) • At programmed FPGA level - in-circuit test of function and timing


  43. Language Construct Templates RTL HDL Files HDL Module Frameworks Xilinx HDL/Core Design Flow - HDL Editing Accessed within HDL Editor DESIGN WIZARD LANGUAGE ASSISTANT HDL EDITOR

  44. HDL instantiation module for core_name Xilinx HDL/core Design Flow - Core Generation Select core and specify input parameters CORE GENERATOR EDIF netlist for core_name Other core_name files

  45. HDL instantiation module for core_names EDIF netlists for core_names Xilinx HDL/core Design Flow - HDL Functional Simulation Set Up and Map work Library RTL HDL Files Testbench HDL Files Compile HDL Files Test Inputs or Force Files MODELSIM Functional Simulate Waveforms or List Files

  46. EDIF netlists for core_names Xilinx HDL Design Flow - Synthesis All HDL Files Edit FPGA Express Synthesis Constraints Select Top Level Synthesis/Implement-ation Constraints Select Target Device FPGA EXPRESS Synthesize Gate/Primitive Netlist Files (EDIF or XNF) Synthesis Report Files

  47. Xilinx HDL/core Design Flow - Implementation Gate/Primitive Netlist Files (XNF or EDN) Netlist Translation XILINX DESIGN MANAGER Map Place & Route Model Extraction Timing Model Gen HDL or EDIF for Implemented Design Create Bitstream Standard Delay Format File BIT File

  48. Xilinx HDL/core Design Flow - Timing Simulation HDL or EDIF for Implemented Design Standard Delay Format File Set Up and Map work Directory Testbench HDL Files Compile HDL Files MODELSIM Test Inputs, Force Files Compiled HDL HDL Simulate Waveforms or List Files

  49. Xilinx HDL Design Flow - Programming and In-circuit Verification Bit File Input Byte GXSLOAD GXSPORT ECE 554 FPGA Board Other Inputs Outputs

  50. Design References -1 • There are two Xilinx 4.2i releases • 4.2i : uses Synopsys FPGA Express synthesis tool (we use this one) • ISE 4.2i: uses Xilinx XST synthesis tool • The manuals are a bit mixed – Do not use material related to XST • Manuals (are provided on website and in tools) • • FPGA complier II/FPGA express Verilog HDL reference manual - essential guide to writing Verilog for FPGA express - suggest you download and print a copy for your use 2 pages/page • Synthesis and simulation design guide - lots of useful information on writing HDL code • CORE generator guide - you will use cores lots, so can be useful.