Topic3:Verification and Test Verilog for Verification 。Testbench anatomy Behavioral modeling for Testbench 。Some examples Timing specification 。Delay model 。Timing verification 。Pipeline technology Design For Test(DFT) Test vs.Verification Build In Self Test (BIST) Scan and Boundary Scan 2021/1/13 ASIC Design,by Yan Bo 3
ASIC Design, by Yan Bo Topic3： Verification and Test Verilog for Verification • Testbench anatomy • Behavioral modeling for Testbench • Some examples Timing specification • Delay model • Timing verification • Pipeline technology Design For Test (DFT) Test vs. Verification Build In Self Test (BIST) Scan and Boundary Scan 2021/1/13 3
Simulation with a Testbench timescale 1 ns/100 ps module Chap1CounterTester ( module Chap1Counter(Clk,Reset,Count): input Clk,Reset: Verilog Testbench reg Clk=0,Reset=0; wire [3:0]Count; output [3:0]Count; Code of a for the Counter Circuit initial begin reg [3:0]Count; Counter Reset=0;#5 Reset=1;#115 Reset=0; always @(posedge Clk)begin Circuit #760 Sstop; if (Reset)Count 0; end else CountCount +1; always #26.5 Clk =Clk: end Chap1Counter U1 (CIk,Reset,Count); endmodule endmodule Testbench Simulator Design to Simulate Name 1,100.1·2001,300·1,4001.5001·600 Clk The simulation Reset results in form of a 0 waveform Count 80 3 2021/1/13 ASIC Design,by Yan Bo 4
ASIC Design, by Yan Bo Simulation with a Testbench Testbench for the Counter Circuit Verilog Code of a Counter Circuit `timescale 1 ns / 100 ps module Chap1CounterTester (); reg Clk=0, Reset=0; wire [3:0] Count; initial begin Reset = 0; #5 Reset = 1; #115 Reset = 0; #760 $stop; end always #26.5 Clk = ~ Clk; Chap1Counter U1 (Clk, Reset, Count); endmodule module Chap1Counter (Clk, Reset, Count); input Clk, Reset; output [3:0] Count; reg [3:0] Count; always @(posedge Clk) begin if (Reset) Count = 0; else Count = Count + 1; end endmodule Simulator Testbench Design to Simulate The simulation results in form of a waveform 2021/1/13 4
TestBench Anatomy module My_tb; --TestBench module has no ports reg.… --Local signals and constants 土 wire......... TestBench Module Instantiating module; -Instantiations of DUT initial begin .........end --Input stimuli:clock Stimulus Generater Apply Inputs initial begin .........end --Input stimuli:reset initial begin .........end --Input stimuli:other signals initial begin ........end --Expected output Design Module Design Under Test always @posedge clock begin --Compare results end Response Monitor Observe Outputs always @posedge clock begin -Display results end endmodule 2021/1/13 ASIC Design,by Yan Bo 5
ASIC Design, by Yan Bo TestBench Anatomy TestBench Module Design Module Stimulus Generater Apply Inputs Response Monitor Observe Outputs 2021/1/13 5 module My_tb; --TestBench module has no ports reg ……….; --Local signals and constants wire ……….; Instantiating module; -- Instantiations of DUT initial begin ……… end -- Input stimuli: clock initial begin ……… end -- Input stimuli: reset initial begin ……… end -- Input stimuli: other signals initial begin ……… end -- Expected output always @ ( posedge clock ) begin ……… -- Compare results end always @ ( posedge clock ) begin ……… -- Display results end endmodule Design Under Test
A Simple Tester Time unit timescale 1ns/100ps------- module Detector110Tester;--No inputor output ports reg aa,clock,rstiInputs&Outputs of DUT wire ww; Detector110 UUT (aa,clock,rst,ww);----The Instantiation ofDUT(Detector110 Module) initial begin aa =0;clock 0;rst =1;--------An initial statement end Generates a periodic signal initial repeat (44)#7 clock ~clock; ← repeats(44)times with(7time steps)delay, initial repeat (15)#23 aa ~aa; initial begin #31rst=1;<-------= Generates a no-periodic signal #23rst=0; end A Verilog System Task:reports the Times always @(ww)if (ww =1) at which the ww Variable becomes 1 Sdisplay ("A 1 was detected on w at time =%t",Stime); endmodule 2021/1/13 ASIC Design,by Yan Bo 6
ASIC Design, by Yan Bo A Simple Tester `timescale 1ns/100ps module Detector110Tester; reg aa, clock, rst; wire ww; Detector110 UUT (aa, clock, rst, ww); initial begin aa = 0; clock = 0; rst = 1; end initial repeat (44) #7 clock = ~clock; initial repeat (15) #23 aa = ~aa; initial begin #31 rst = 1; #23 rst = 0; end always @(ww) if (ww == 1) $display ("A 1 was detected on w at time = %t", $time); endmodule No input or output ports Inputs & Outputs of DUT The Instantiation of DUT (Detector110 Module) An initial statement Generates a periodic signal : repeats (44) times with (7time steps) delay, Generates a no-periodic signal A Verilog System Task: reports the Times at which the ww Variable becomes 1 Time unit 2021/1/13 6
Units of time Unit Definition fs femtoseconds(10-15 seconds) ps picoseconds(10-12 seconds) ns (1GHz) nanoseconds(10-9 seconds) us microseconds(10-6 seconds) ms miliseconds (10-3 seconds) sec seconds min minutes(60 seconds) hr hours(3600 seconds) ASIC Design,by Yan Bo
ASIC Design, by Yan Bo 7 Units of time Unit Definition fs femtoseconds (10-15 seconds) ps picoseconds (10-12 seconds) ns nanoseconds (10-9 seconds) us microseconds (10-6 seconds) ms miliseconds (10-3 seconds) sec seconds min minutes (60 seconds) hr hours (3600 seconds) (1GHz)
Topic3:Verification and Test Verilog for Testbench 。Testbench anatomy Behavioral modeling for Testbench 。Some examples Timing specification 。Delay model 。Timing verification 。Pipeline technology Design For Test(DFT) Test vs.Verification Build In Self Test (BIST) Scan and Boundary Scan 2021/1/13 ASIC Design,by Yan Bo 8
ASIC Design, by Yan Bo Topic3： Verification and Test Verilog for Testbench • Testbench anatomy • Behavioral modeling for Testbench • Some examples Timing specification • Delay model • Timing verification • Pipeline technology Design For Test (DFT) Test vs. Verification Build In Self Test (BIST) Scan and Boundary Scan 2021/1/13 8
Description Levels of HDL Testbenches Formal documentation, 业 to communicate structural dataflow behavioral with other designers (sequential) Components and Concurrent interconnects statements 水 Subsetmostsuitable Registers State machines for synthesis一 Decoders HDL for Specification HDL for Simulation Test and verify a design (Feed it), to input to a simulator HDL for Synthesis (For Real Hardware) Realize and Iterate a digital logic design,to input to a synthesizer 2021/1/13 ASIC Design,by Yan Bo
ASIC Design, by Yan Bo 9 Description Levels of HDL HDL for Specification HDL for Simulation HDL for Synthesis (For Real Hardware) Formal documentation, to communicate with other designers Test and verify a design (Feed it), to input to a simulator Realize and Iterate a digital logic design, to input to a synthesizer 2021/1/13 Components and interconnects structural behavioral (sequential) Registers State machines Decoders Subset most suitable for synthesis Testbenches dataflow Concurrent statements
Components of a Verilog Module module Timing Specifications (Port List) Port Data Type Circuit Subprograms Declarations Declarations Functionality Instantiation task input net Continuous Procedural function output register Assignment Blocks System Tasks always inout parameter assign block Compiler Directives initial block 2021/1/13 ASIC Design,by Yan Bo 10
ASIC Design, by Yan Bo Components of a Verilog Module module (Port List) Port Declarations input output inout Data Type Declarations net register parameter Circuit Functionality Timing Specifications Continuous Assignment assign Procedural Blocks always block Subprograms task function System Tasks Compiler Directives Instantiation initial block 2021/1/13 10
Initial and Always Blocks initial Runs when simulation starts begin >Terminates when control ..imperative statements... reaches the end end >Good for providing stimulus always Runs when simulation starts begin Restarts when control reaches ..imperative statements... the end end > Good for modeling/specifying hardware 2021/1/13 ASIC Design,by Yan Bo 11
ASIC Design, by Yan Bo Initial and Always Blocks initial begin … imperative statements … end always @ ( ) begin … imperative statements … end ➢Runs when simulation starts ➢Terminates when control reaches the end ➢Good for providing stimulus ➢Runs when simulation starts ➢Restarts when control reaches the end ➢Good for modeling/specifying hardware 2021/1/13 11
Blocking vs.Non-blocking Assignments Blocking (= Nonblocking (<= initial initial begin begin a=#5b; a<=#5b; c=#10d; C<=#10d; end end a=b c=d a=b c=d 5 10 15 5 10 15 2021/1/13 ASIC Design,by Yan Bo 12
ASIC Design, by Yan Bo Blocking vs. Non-blocking Assignments Blocking (=) Nonblocking (<=) initial begin a =#5 b; c =#10 d; end initial begin a <=#5 b; c <= #10 d; end 5 10 15 a=b c=d 5 10 15 a=b c=d 2021/1/13 12