Prof. John Nestor ECE Department Lafayette College Easton, Pennsylvania ECE VLSI System Design Lecture 12 - Timing, Project Overview

3/10/03Lecture 12 - Timing, Proj. Overview 2 Announcements  Exam 1 - Take-Home  Out: March 24  Due: March 31  Timing References  Synopys Online Documentation (SOLD) Manuals - access using the "sold" command: Design Compiler User Guide Design Compiler Tutorial Design Compiler Reference Manual  Pran Kurup and Taher Abbasi, Logic Synthesis using Sysnopsys®, 2nd ed., Kluwer Academic Publishers, 1997.

3/10/03Lecture 12 - Timing, Proj. Overview 3 Where we are...  Last Time  State Coding & Assignment  Timing  Today  Timing in Synopsys Tools  Project Overview

3/10/03Lecture 12 - Timing, Proj. Overview 4 Timing in the Design Compiler  DC assumes a synchronous, clock-based system  Derives setup, hold constraints between registers  User-specified timing constraints on inputs, outputs DQ DQ DQ DQ Comb. Logic (Internal) Comb. Logic (Output) Comb. Logic (Input) Register-Register Timing Paths Input Timing Paths Output Timing Paths

3/10/03Lecture 12 - Timing, Proj. Overview 5 Specifying Timing in Synopsys DC  Clock specification (See last lecture slide 37-38)  Period  Skew (and uncertainty)  Input constraints  Output constraints  Combinational delay constraints  Special cases  false paths  multicycle paths

3/10/03Lecture 12 - Timing, Proj. Overview 6 Input Constraints: A Closer Look  Rationale:  assume input is tied to some "other" module  input delay = output delay of other module  Example: set_input_delay 17 -clock clk d1 d1 17 ns clk 17 ns d1 comb. logic D Q comb. logic "current design" module clk comb. logic D Q "other" module

3/10/03Lecture 12 - Timing, Proj. Overview 7 Input Constraints: A Closer Look  Impacts delay of input logic (of current design)  Creates maximum timing constraint for setup time  Creates minimum timing constraint for hold time d1 17 ns clk comb. logic D Q "other" module d1 input logic D Q comb. logic "current design" module 17 ns t ci t su

3/10/03Lecture 12 - Timing, Proj. Overview 8 Output Constraints: A Closer Look  Rationale:  assume output is tied to some "other" module  output delay = input delay of other module + setup time  Example: set_output_delay 5 -clock clk d1 d2 5 ns clk d2 comb. logic D Q output logic "current design" module 15 ns comb. logic D Q "other" module

3/10/03Lecture 12 - Timing, Proj. Overview 9 Output Constraints: A Closer Look  Impacts delay of output logic (of current design)  Creates maximum timing constraint for setup time  Creates minimum timing constraint for hold time d2 5 ns clk comb. logic comb. logic D Q D Q output logic "current design" module "other" module clk 15 ns t co t pff

3/10/03Lecture 12 - Timing, Proj. Overview 10 Timing Constraints Example  VHDL Code: library ieee; use ieee.std_logic_1164.all; entity timing_ex is port( a, b, clk, reset : in std_logic; d : out std_logic ); end; architecture behavior of timing_ex is signal f : std_logic; begin process (clk, reset) begin if (reset = '0') then f <= '0'; elsif (rising_edge(clk)) then f <= a; end if; end process; process (clk, reset) begin if (reset = '0') then d<='0'; elsif (rising_edge(clk)) then d <= f and b; end if; end process; end;

3/10/03Lecture 12 - Timing, Proj. Overview 11 Timing Constraints Example  Timing Constraints: create_clock clk -period 10.0 set_fix_hold clk /* check hold time */ set_input_delay 0.5 -clock clk {a,b} set_output_delay 1.0 -clock clk d ;  Synthesized Design:

3/10/03Lecture 12 - Timing, Proj. Overview 12 Getting Timing Reports:  Seeing timing results: report_timing command report_timing -max_paths 5  Result: **************************************** Report : timing -path full -delay max -max_paths 5 Design : timing_ex Version: Date : Thu Apr 5 15:26: **************************************** Operating Conditions: Wire Load Model Mode: top (continued)

3/10/03Lecture 12 - Timing, Proj. Overview 13 Timing Report - Register to Register Startpoint: f_reg (falling edge-triggered flip-flop clocked by clk') Endpoint: d_reg (falling edge-triggered flip-flop clocked by clk') Path Group: clk Path Type: max Point Incr Path clock clk' (fall edge) clock network delay (ideal) f_reg/CLK2 (dfrf301) f f_reg/Q (dfrf301) f U32/O2 (nanf211) f d_reg/DATA1 (dfrf301) f data arrival time 1.33 clock clk' (fall edge) clock network delay (ideal) d_reg/CLK2 (dfrf301) f library setup time data required time data required time 9.74 data arrival time slack (MET) 8.41

3/10/03Lecture 12 - Timing, Proj. Overview 14 Timing Report - Output Logic Startpoint: d_reg (falling edge-triggered flip-flop clocked by clk') Endpoint: d (output port clocked by clk) Path Group: clk Path Type: max Point Incr Path clock clk' (fall edge) clock network delay (ideal) d_reg/CLK2 (dfrf301) f d_reg/Q (dfrf301) f d (out) f data arrival time 0.97 clock clk (rise edge) clock network delay (ideal) output external delay data required time data required time 9.00 data arrival time slack (MET) 8.03

3/10/03Lecture 12 - Timing, Proj. Overview 15 Timing Report - Input Logic Startpoint: a (input port clocked by clk) Endpoint: f_reg (falling edge-triggered flip-flop clocked by clk') Path Group: clk Path Type: max Point Incr Path clock clk (rise edge) clock network delay (ideal) input external delay f a (in) f f_reg/DATA1 (dfrf301) f data arrival time 0.50 clock clk' (fall edge) clock network delay (ideal) f_reg/CLK2 (dfrf301) f library setup time data required time data required time 9.77 data arrival time slack (MET) 9.27

3/10/03Lecture 12 - Timing, Proj. Overview 16 Other Timing Constraint Functions  Tell timing analyzer to ignore a false path set_false_path -from source -to dest  Specify combinational delays set_min_delay amt -from source -to dest set_max_delay amt -from source -to dest  Specify multicycle path of N cycles set_multicylce_path N -from source -to dest

3/10/03Lecture 12 - Timing, Proj. Overview 17 How DC Works With Constraints  Compile (Optimization) Steps  Initial mapping to gates in library  Delay optimization: attempt to fix constraint violations  Design rule fixing: attempt to fix design rule violations  Area optimization: attempt to meet area constraints without creating timing violations  What happens when DC can't meet constraints  Apply flattening (if you can afford to)  Re-work constraints

3/10/03Lecture 12 - Timing, Proj. Overview 18 Using DC With Large Designs  DC can't optimize large designs as one unit  Typical approach: use hierarchy to control  Control runtime  Control optimization strategy

3/10/03Lecture 12 - Timing, Proj. Overview 19 Using DC With Large Designs (cont'd)  Compilation strategies  Top-down - compile all submodules together  Bottom-up - compile leaf modules first, then move up (use "characterize" commands to get input, output delays)  Mixed - use different approaches as appropriate in different levels of hierarchy

3/10/03Lecture 12 - Timing, Proj. Overview 20 Synthesize Blocks / Timing Analysis Timing OK? Place & Route / Timing Analysis Timing OK? N N Y Y DONE START Design Compiler Circuit extraction provides accurate timing; "Back Annotation"identifies critical paths Timing in Design Flow - ASIC Design

3/10/03Lecture 12 - Timing, Proj. Overview 21 Project Overview - WimpNet03  Key idea: computers communicate on shared wires (ether)  Each computer has 8-bit address  Information passed as packets

3/10/03Lecture 12 - Timing, Proj. Overview 22 Packet Format  Header  destination address (8 bits)  source address (8 bits)  length (8 bits)  Data - up to 255 bytes  CRC Byte - Error Code All bytes transmitted with LSB first

3/10/03Lecture 12 - Timing, Proj. Overview 23 Control Procedure - CSMA/CD  CSMA/CD  Carrier Sense Multiple Access with Collision Detection  Procedure  Defer - don’t transmit when carrier sense  Transmit - transmit while monitoring data  Collision - error in transmission when two stations transmit at same time  Abort - terminate transmission and jam 4-6 bytes  Backoff - wait for a random retransmission delay  Retransmit - try again after backoff

3/10/03Lecture 12 - Timing, Proj. Overview 24 Project Goals  Build a complete WimpNet03 Interface Chip  Receiver with buffer RAM  Transmitter with buffer RAM  Area budget: 4 MOSIS Tiny Chips (4400 X 4400 )

3/10/03Lecture 12 - Timing, Proj. Overview 25 Transmitter Details

3/10/03Lecture 12 - Timing, Proj. Overview 26 Receiver Details

3/10/03Lecture 12 - Timing, Proj. Overview 27 RAM Subsystem Details  Two-port organization  Write port - writes on falling edge of clk when w_en_l =L  Read port  Size: 256 Bytes

3/10/03Lecture 12 - Timing, Proj. Overview 28 Design Groups  Receiver Design  Transmitter Design  RAM Subsystem Design  Chip assembly

3/10/03Lecture 12 - Timing, Proj. Overview 29 Coming Up  More about the Project  Subsystem Design: RAM