Homework 2 arbiter and test bench verilog

Arbiter Operates: Arbiter is a device used in a multimaster bus system to decide which bus masterwill be allowed to control the bus for each bus cycle. The input of arbiter inclusion: request (8bits), priority (24bits), roundORpriority(1bit), reset (1bit), clock. The output of arbiter inclusion: bits of grant (8bits)

VLSI DESIGN AUTOMATION

Homework #2, 2-1

Test bench for Arbiter

Student: Bui Huu Nguyen

ID number: 2016310539

Submission Date: 2016/10/06

Update Date: 2016/10/12

Arbiter

ENB

ENB

ENB

ENB ENB

ENB

ENB

ENB

Grant-8bits [7:0]

BUS

[7:0]

Arbiter

CPU

Priority-24bits Request-8bits RoundORpriority-1bit Reset-1bit Clock

Figure 1: Diagram input and output of Arbiter Arbiter Operates:

- Arbiter is a device used in a multi-master bus system to decide which bus master will be allowed to control the bus for each bus cycle

- The input of arbiter inclusion: request (8bits), priority (24bits), roundORpriority (1bit), reset (1bit), clock

- The output of arbiter inclusion: bits of grant (8bits)

A Write test bench

1 Selection bit roundORpriority equal 0 that has round mode

0-1-2-3-4-5-6-7

Figure 2: Round mode a) Single request

- Value of input “request” will be changed one bit flowing table

00000001 00000010 00000100 00001000 00010000 00100000 01000000 10000000

b) Multi request

- Value of input “request” will be changed as flowing table

11000000 11100000 00001111 11110000 11100111

2 Selection bit roundORpriority equal 1 that has priority mode

c) Multi request with different priority

- Set input “priority” to a specific value:

Request: 7-6-5-4-3-2-1-0

Order: 5-6-7-0-1-2-3-4

 Priority: 24’b101-110-111-000-001-010-011-100

- Value of input “request” will be changed as flowing table

11100000 01110000 01111000 $ramdom()

d) Multi request with random priority

- priority = $random();

e) Multi request with random request and priority

- request = $random(); priority = $random();

Code Abiter test bench

`timescale 1ns / 100 ps

module arbiter_tb();

//integer i,j,k,p,q,r,s,t,u,v ; //index for "for" loops

// -

// parameters

// -

parameter NUMUNITS = 8;

parameter ADDRESSWIDTH = 3; //number of bits needed to address NUMUNITS // -

// input and output declarations

// -

reg clock;

reg reset;

reg roundORpriority;

reg [NUMUNITS-1 : 0] request;

reg [ADDRESSWIDTH*NUMUNITS-1 : 0] priority;

wire [NUMUNITS-1 : 0] grant;

//arbiter x(clock, reset, roundORpriority, request, priority,grant);

initial begin

reset = 0;

clock = 0;

request = 8'b0;

roundORpriority = 1'b0; // round mode priority = 24'h000000;

#10 reset = 1;

//roundORpriority = 2'b00;

//single request

request = 8'b00000001;

#10

request = 8'b00000010;

#10

request = 8'b00000100;

#10

request = 8'b00001000;

#10

request = 8'b00010000;

#10

request = 8'b00100000;

#10

request = 8'b01000000;

#10

request = 8'b10000000;

//multi request

#10

request = 8'b11000000;

#10

request = 8'b11100000;

#10

request = 8'b00001111;

#10

request = 8'b11110000;

#10

request = 8'b11100111;

//Priority mode

roundORpriority = 1'b1; // priority mode

priority = 24'b101110111000001010011100; // 7-6-5-4-3-2-1-0 request, 5-6-7-0-1-2-3-4 priority

#10

request = 8'b11100000;

#10

request = 8'b01110000;

#10

request = 8'b01111000;

#10

request = $random(); // random request

// random priority

#10

priority = $random();

#10

request = 8'b11100000;

#10

request = 8'b01110000;

#10

request = 8'b01111000;

// random priority and random request

#10

priority = $random();

#10

request = $random();

end

always #5 clock = ! clock;

arbiter u0(.clock (clock),.reset (reset),.roundORpriority (1'b0),.request(request),.priority (priority),.grant (grant));

endmodule

B Simulation result

1 RoundORpriority = 0, round mode

a) Single request

-request: 00000001->grant:00000001

b Multi request

-request: 10000000  grant: 10000000 (7)

-request: 11000000  grant: 01000000 (6)

-request: 11100000  grant: 10000000 (7)

-request: 00001111  grant: 00000001 (1)

2 RoundORpriority = 0, priority mode

0-1-2-3-4-5-6-7

-request: 11100000  grant: 10000000

-request: 01110000  grant: 00010000

-request: 01111000  grant: 00010000

-request: 00100100  grant: 00000100 (random request)

3 Multi request with random priority

-priority: 24’h895e81 = 24’b100-010-010-101-111-010-000-001

-Order: 4-2-2-5-7-2-0-1

-request: 7-6-5-4-3-2-1-0

-request: 11100000  grant: 0100000

-request: 01110000  grant: 0100000

-request: 01111000  grant: 0010000

4 Multi request with random request and priority

-priority: 24’h84d609 = 24’b100-001-001-101-011-000-001-001

-Order: 4-1-1-5-3-0-1-1

-request: 7-6-5-4-3-2-1-0

-request: 01100011  grant: 0100000 or 00000001 or 00000010 or 00100000 or

01000000

Homework 2-1

1 Seeded random function with range definition

request = $random(seed)%(32'b1<<8);

priority = $random(seed)%(32'b1<<24);

2 Check output of ‘grant’ output is ‘xxx’

task check_func;

input [NUMUNITS-1:0] request;

reg [NUMUNITS-1:0] expected_grant;

integer j,k,m, min, index1;

integer index[7:0];

reg [ADDRESSWIDTH-1:0] prio[7:0];

reg [ADDRESSWIDTH-1:0] tmp_prio;

begin

#1;

k=0;

for(j=NUMUNITS-1; j>=0; j=j-1) begin

if (old_request[j]) begin

for(m=0;m<ADDRESSWIDTH;m=m+1)

tmp_prio[m]=old_priority[j*ADDRESSWIDTH + m];

prio[k] = tmp_prio;

index[k] = j;

k=k+1;

end

end

min =NUMUNITS-1;

for(j=0; j<k; j=j+1) begin

// $display("request=%8b, index=%0d, priority=%0d", old_request, index[j], prio[j]);

if(min >= prio[j]) begin

min = prio[j];

index1=index[j];

end

end

// $display("request=%8b, index_max=%0d", old_request, index1);

expected_grant=old_request==0 ? 8'h00 : 8'h01 << index1;

if(grant==expected_grant)

$display(" -@%4d Request = %8b, Real_Grant = %8b, Expected_Grant = %8b => CORRECTLY", $time, old_request,

grant, expected_grant);

else

$display(" -@%4d Request = %8b, Real_Grant = %8b, Expected_Grant = %8b => INCORRECTLY", $time, old_request,

grant, expected_grant);

old_request = request;

old_priority = priority;

end

endtask

///Update code Arbiter 10/12/2016

`timescale 1ns / 100 ps

module arbiter_tb();

//integer i,j,k,p,q,r,s,t,u,v ; //index for "for" loops

integer seed;

// -

// parameters

// -

parameter NUMUNITS = 8;

parameter ADDRESSWIDTH = 3; //number of bits needed to address NUMUNITS // -

// input and output declarations

// -

reg clock;

reg reset;

reg roundORpriority;

reg [NUMUNITS-1 : 0] request;

reg [ADDRESSWIDTH*NUMUNITS-1 : 0] priority;

wire [NUMUNITS-1 : 0] grant;

reg [NUMUNITS-1 : 0] old_request;

reg [ADDRESSWIDTH*NUMUNITS-1 : 0] old_priority;

//arbiter x(clock, reset, roundORpriority, request, priority,grant);

initial begin

reset = 0;

clock = 0;

request = 8'b0;

roundORpriority = 1'b0; // round mode

priority = 24'h000000; #6 reset = 1;

//roundORpriority = 1'b0; //single request

request = 8'b00000001; check_func(request);

#10

request = 8'b00000010; check_func(request);

#10

request = 8'b00000100; check_func(request);

#10

request = 8'b00001000; check_func(request);

#10

request = 8'b00010000; check_func(request);

#10

request = 8'b00100000; check_func(request);

#10

request = 8'b01000000; check_func(request);

#10

request = 8'b10000000; check_func(request); //multi request

#10

request = 8'b11000000; check_func(request);

#10

request = 8'b11100000; check_func(request);

#10

request = 8'b00001111;

check_func(request);

#10

request = 8'b11110000;

check_func(request);

#10

request = 8'b11100111;

check_func(request);

//Priority mode

roundORpriority = 1'b1; // priority mode

priority = 24'b101110111000001010011100; // 7-6-5-4-3-2-1-0 request, 5-6-7-0-1-2-3-4 priority

#10

request = 8'b11100000;

check_func(request);

#10

request = 8'b01110000;

check_func(request);

#10

request = 8'b01111000;

check_func(request);

#10

request = $random(seed)%(32'b1<<8); // random request

check_func(request);

// random priority

#10

priority = $random(seed)%(32'b1<<24);

check_func(priority);

#10

request = 8'b11100000;

check_func(request);

#10

request = 8'b01110000;

check_func(request);

#10

request = 8'b01111000;

check_func(request);

// random priority and random request

#10

priority = $random(seed)%(32'b1<<24);

$display("@%4d -PRIORITY %24b -", $time, priority); check_func(request);

#10

request = $random(seed)%(32'b1<<8);

check_func(request);

end

always #5 clock = ! clock;

// check function

task check_func;

input [NUMUNITS-1:0] request;

reg [NUMUNITS-1:0] expected_grant;

integer j,k,m, min, index1;

integer index[7:0];

reg [ADDRESSWIDTH-1:0] prio[7:0];

reg [ADDRESSWIDTH-1:0] tmp_prio;

begin

#1;

k=0;

for(j=NUMUNITS-1; j>=0; j=j-1) begin

if (old_request[j]) begin

for(m=0;m<ADDRESSWIDTH;m=m+1)

tmp_prio[m]=old_priority[j*ADDRESSWIDTH + m];

prio[k] = tmp_prio;

index[k] = j;

k=k+1;

end

end

min =NUMUNITS-1;

for(j=0; j<k; j=j+1) begin

// $display("request=%8b, index=%0d, priority=%0d", old_request, index[j], prio[j]);

if(min >= prio[j]) begin

min = prio[j];

index1=index[j];

end

end

// $display("request=%8b, index_max=%0d", old_request, index1);

expected_grant=old_request==0 ? 8'h00 : 8'h01 << index1;

if(grant==expected_grant)

$display(" -@%4d Request = %8b, Real_Grant = %8b, Expected_Grant = %8b => CORRECTLY", $time, old_request,

grant, expected_grant);

else

$display(" -@%4d Request = %8b, Real_Grant = %8b, Expected_Grant = %8b => INCORRECTLY", $time, old_request,

grant, expected_grant);

old_request = request;

old_priority = priority;

end

endtask

arbiter u0(.clock (clock),.reset (reset),.roundORpriority (1'b0),.request(request),.priority (priority),.grant (grant));

endmodule

Results:

3 Review “DUT” why ‘grant’ output is ‘xxx’ when the ‘rst’ is less than first up of clock Change “DUT” as asysnc, rst, and simulation

Answer:

Because reset is active at ‘0’ level, if rising of reset happens after 1st positive edge clock then system is reset, some internal signals (grantD, scan, next, nextNext) would be zero, not unknown

If reset is set to ‘1’ level before rising edge of 1st clock, at 1st positive edge of clock, reset is in-active, so system is still not reset, some internal signals (grantD, scan, next, nextNext) is unknown value, therefore, the output grant also is unknown until reset is active again

Change synchronous reset to asynchronous reset and run simulation In file arbiter.v, we modify reg_code become:

And we obtain result: