IntroToSV_orgi

Intro To SystemVerilog

SystemVerilog for Verification

Day One

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Welcome

� Welcome to the “Intro to SystemVerilog for Verification” class

� Requirements� Some HDL programming experience� Some Unix experience� Familiarity with some Unix editor� Unix account in Folsom, Chandler, Dupont, or

Penang.

� Assumes use of Modelsim.

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Scope Of Course

� Introduction to SystemVerilog for verification� Hands-on lab assignments� Students will not be SystemVerilog experts at the

end of this class. Class is an introduction only. Advanced classes go into more details.� Next Classes:

� Functional Coverage/Temporal language/Checkers� How to write a SV Test� How to write an SV BFM

� Length: 2 days

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Typographic Conventions

Regular Text

Courier Bold

Courier Regular

Italic

Course Content

Code examples, command line keyboard input

Screen output

Placeholders for data user should input

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What is SystemVerilog

SystemVerilog is an IEEE extension to the Verilog language.

SystemVerilog adds testbench features such as classes, constraints, and temporal expressions to Verilog.

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Getting More Information

� SystemVerilog LRMhttp://www.eda.org/sv/SystemVerilog_3.1a.pdf

� AVC Wikihttp://www-

fmec.fm.intel.com/twiki/bin/view/Chipset/SystemVerilog

� Comprehensive information on SV:http://carmel.fm.intel.com/sites/CPD-CDTG/DATE/FEDAO/SystemVerilog%20Deployment%20Doc%20Lib/Forms/AllItems.aspx

� Additional Informationwww.accellera.org

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Using SystemVerilog

To setup your environment to use SystemVerilog, type the following at the unix prompt:

% source <local site specific setup script>

Next, create a training directory, and create a work library:

% mkdir svtraining; cd svtraining% vlib work% vmap work work

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Hello World

module helloWorld();

initial

begin: hello

$display("Hello World");

end: hello

endmodule: helloWorld

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Compiling SystemVerilog

To compile your program, type the following:

% vlog hello.sv

Note: If you do not name your file ending in .sv, you must use the –sv option to vlog.

To run your program, use the following command:

% vsim -c -do "run -all;q -f" helloWorld


Commenting Your Code

Like C++, SystemVerilog supports two types of comments

/* Block comments that can span

* multiple lines

*/

// And single line comments

$display(“hello”); // This is a comment


Lab 1: Hello World

Create a module that prints “Hello World” using the $display command.

Basic Data Types


Integer Data Type

4-state, 64 bit unsignedtime4-state, 32 bit signedinteger4-state user-defined sizereg4-state (1,0,x,z) user-deflogic2-state, user-defined vector sizebit2-state, 8 bit signedbyte2-state, 64 bit signedlongint2-state, 32 bit signedint2-state (1, 0), 16 bit signedshortint


Signed/Unsigned

� byte, shortint, int, integer and longint defaults to signed� Use unsigned to represent unsigned integer value

Example: int unsigned ui;

� bit, reg and logic defaults to unsigned� To create vectors, use the following syntax:

logic [1:0] L; // Creates 2 bit logic

// vector


Strings

� string – dynamic allocated array of bytes� SV provides methods for working with strings

indexing – return 0 if out of range

Str1[index]

Concatenation{Str1, Str2, … Strn}

Comparison<, <=, >, >=

InequalityStr1 != Str2

EqualityStr1 == Str2


String Methods

� len

� putc

� getc

� toupper

� tolower

� compare

� icompare

� substr

� atoi, atohex, atoct, atobin

� atoreal

� itoa

� hextoa

� octtoa

� bintoa

� realtoa


Literal Values

� Integer Literal – Same as verilog� value – unsized decimal value� size’base value – sized integer in a specific radix

� Ex: 4’b0101; 4’hC; 32’hDEAD_BEEF; 2’b1Z

� Real Literal� value.value

� Ex: 2.4� Base Exponent ( E/e)

� Logic Value� 0, 1, [z|Z], [x|X]


Lab 2: Data TypesWrite a top level module that displays the following output.Use of the following data types:1. int both signed and unsigned2. logic3. string

Hint:int i, h; $display(“%d %h”, i, h);

string str; $sformat(str, “%b”, l)$display(“Logic value in upper case %s”,str.toupper());

Output:# The integer i is 0x00000014# The unsigned integer ui is 0xdeadbeef# The logic L is 1Z # string str1 is "Hello World"# string str2 is "Cruel World“


Operators

Logic Operators& | ~ ^ ~& ~| ~^ << >>

Arithmetic Operators+ - % / * ** <<< >>>

Assignment Operators= += -= *= /= %= &= |= ^= <<= >>= <<<= >>>=

Example:a += 3;Equivalent to:a = a + 3;


Operators

Auto-increment (++) Auto-decrement(--)Example:a = 1; a++;a now contains 2.

Comparison Operators== != === !== =?= !?= > < <= >=

Example:a = 1'bZ; b = 1'bZ;if (a != b) $display(“Z != Z”);

if (a === b) $display(“Z === Z”);


Concatenation

The { } operator is used for concatenation. Example:s = {“Hello”, “ “, “World”};v = {32’b1, 32’b10}; // v = 64b vector

Can also be used on left hand side:{a, b, c} = 3’b111;

Sizes of assignment have to match. If LHS is smaller then assignment gets

truncated.


Lab 3: Operators

Write a SystemVerilog module to calculate the following, and print the result as an integer to the screen:

(1101001 XOR 11111001) ÷ 5

Ignore remainder.

Flow Control Constructs

How to go with the flow


SystemVerilog additions

� Verilog includes: if-(else-(if)), case, forever, repeat, while, for, ?: (ternary)

� SystemVerilog:� Enhances for� Adds do..while, foreach


if

Verilog ‘if’ expressionsThen branch taken for any nonzero known value of expr (no ‘x’ or

‘z’), equivalent to expr != ‘0’Chain ‘if’ statements:

if (expr)begin…end

else if (expr) begin…end

elsebegin…end


?:

Operator, but conditionalexpr ? then_val : else_val

Some call this the “ternary” operator, in the same vein as “unary” and “binary”, with 3 operands.

Ex: var_m = (x == 1) ? a : b;


case

� 4-value exact matching, runtime evaluation, no fallthrough, bit length of all expressions padded to same length

case (expr)item: begin

statement end

item2, item3, item4:begin statement

enddefault: statement

endcase


casez, casex

Handle wild cards with either casez or casexcasez: ‘z’ bit in either item or expression will be treated

as a match for that bitcasex: ‘z’ or ‘x’ bits will both match

casex (8’bx100z011 ^ reg_a)

8’b1x1001?1: $display(“x”);8’b01z10zx1: $display(“y”);

8’b11z01011: $display(“z”);

endcase


forever

Continuous execution, without end, of body statement(s)

Used with timing controls Usually last statement in some block

initial : clock_drivebegin

clk = 1’b0;forever #10 clk = ~clk;

end : clock_drive


repeat

Repeat a block ‘x’ times, no conditional testrepeat (expr) statement

What happens with expr = ‘x’ or ‘z’?

Examplex = 0;repeat (16) begin

$display(“%d”, x++);end


while

Executes statement as long as expr evaluates to truewhile (expr) statement

Example:while (reg_i) begin

something_happens();

reg_i = reg_i – 1;

end


for

‘C’ inspired for loopfor (initial_assignment; condition; step_assignment)

statement

Equivalent tobegin

initial_assignment;while (condition) begin

statement;step_assignment;

endend


Enhanced for

SystemVerilog adds: Loop variable declarationMultiple statements in init and step blocks (comma

separated)++ and -- operators (Mentioned in operator section)

for (int i; i < arr.size(); j+=2, i++) beginarr[i] += 200;arrb[i]--;

end


do..while

do statement while (expr);

What’s the difference?x = 0;

1) while (x) begin $display(“%d”, x); x--;

end2) do

begin $display(“%d”, x); x--; end

while (x);


Lab 4: Flow control

Write a SystemVerilog module to display the first 20 Fibonacci numbers.

Fn = Fn-1 + Fn-2

� Hint: F1 = F2 = 1

User Defined Types andEnumerated Types

8-38 • SV for Verification Using Questa: Functional Coverage Copyright © 2005 Mentor Graphics Corporation

User Defined Types

SystemVerilog supports a new keyword: typedef

Syntax: typedef <base_data_type> <type_identifier>

typedef int inch ; // inch becomes a new type

inch foot = 12, yard = 36; // these are 2 new variables of type ‘inch’


Enumeration

Enumeration is a useful way of defining abstract variables.

Define an enumeration with “ enum ”enum {red, green, yellow} traf_lite1, traf_lite2;

Values can be cast to integer types and auto-incrementedenum { a=5, b, c} vars; // b=6, c=7

A sized constant can be used to set size of the typeenum bit [3:0] { bronze=4’h3, silver, gold} medal; // All medal members are 4-bits

NOTE:

Default assigned values start at zero

0 1 2enum {red, green, yellow} lite;

Syntax:enum [enum_base_type] { enum_name_declaration {,enum_name_declaration} }

enum_base_type: default is int

Define a new typetypedef enum {NO, YES} bool; // bool is NOT a SystemVerilog typebool myvar; // but it just became one �

“myvar” will now be checked for valid values in all assignments, arguments and relational operators


Enumeration example

Modelsim now allows viewing of enum types inwaveforms similar to VHDL enumtypes.

To use enumerated types in numerical expressionsthe language provides the following functions:prev(), next(), first(), last(), num() and name().

Exampletypedef enum {red, green, blue, yellow,

white, black} Colors;

Colors col_ps;

Colors col_ns;

always @(col_ps)

col_ns = col_ps.next();

always @(posedge clk)col_ps <= col_ns;

Casting


Casting

� A data type can be changed by using a cast (’) operation.

� Syntax: <type>’(<value/expression>)� Examples:

� int’(2.0 * 3.0)// real to int casting

� 7’(x-2)//number of bits to change size.

� signed(m)//changes m to signed

� inteltype’(2+3)//casting to a user defined type [inteltype].

Arrays


Packed/Unpacked Arrays

� In packed arrays [range is on the left side of the identifier] all elements are glued together and can be overwritten by zero/sign extension of a single literal.� Ex: logic [3:0] m;

m = 4’b1100;

� In unpacked arrays [range is on the right side of the identifier] each individual element is considered by itself without any relation to other elements. � Ex: logic m [5:0];

// each element is only 1-bit deep

� Arrays can have packed and unpacked dimensions.� Ex: logic [3:0] m [5:0]


Array Literals and Default

To help in assigning literal values to arrays SV introduces the default keyword:

For more control, consider the dimensions of the array and use { } to match those dimensions exactly.

int k [1:3][1:4] = '{'{1,2,3,4},'{5,6,7,8},'{9,10,11,12}}; // 3 groups of 4

int m [1:2][1:3] = '{'{0,1,2},'{3{4}}}; // 2 groups of 3

int k [1:1000] = '{default: 5}; // All elements “5”


Dynamic Arrays

Dynamic declaration of one index of an unpacked array

Syntax:data_type array_name[] ;

Declares a dynamic array array_name of type data_type

data_type array_name[] = new[ array_size ] [(array)] ;Allocates a new array array_name of type data_type and size array_sizeOptionally assigns values of array to array_nameIf no value is assigned then element has default value of data_type

Examples:bit [3:0] nibble[ ]; // Dynamic array of 4-bit vectorsinteger mem[ ]; // Dynamic array of integers

int data[ ]; // Declare a dynamic arraydata = new[256]; // Create a 256-element arrayint addr = new[100]; // Create a 100-element arrayaddr = new[200](addr); // Create a 200-element array

// preserving previous values in lower 100 addresses

1st new array in SV, not synthesizable


Dynamic Arrays – Methods

function int size()Returns the current size of the array

int addr[ ] = new[256];int j = addr.size(); // j = 256

function void delete()Empties array contents and zero-sizes it

int addr[ ] = new[256];addr.delete();

Cannot delete selected elements


Dynamic Array Examplemodule dyn_arry ();

bit data1 [];initial

begin

// create a 128 element array

data1 = new [128];

$display("Size of array = %d",

data1.size());

data2 = new[256](data1);


data2.size());

data1.delete();


data1.size());

end

endmodule


Queues and Lists

SV has a built-in list mechanism which is ideal for queues, stacks, etc.A list is basically a variable size array of any SV data type.

int q1[$]; // $ represents the ‘upper’ array boundaryint n, item;

q1 = ‘{ n, q1 }; // uses concatenate syntax to write n to the left end of q1q1 = ‘{ q1, n }; // uses concatenate syntax to write n to the right end of q1

item = q1[0]; // read leftmost ( first ) item from listitem = q1[$]; // read rightmost ( last ) item from list

n = q1.size; // determine number of items on q1

q1 = q1[1:$]; // delete leftmost ( first ) item of q1q1 = q1[0:$-1]; // delete rightmost ( last ) item of q1

for (int i=0; i < q1.size; i++) // step through a list using integers (NO POINTERS)begin … end

q1 = { }; // clear the q1 list

3rd new array in SV, not synthesizable


Queue Methods

size() Returns the number of items in the queue. Prototype:If the queue is empty, it returns 0. function int size();

insert() Inserts the given item at the specified index position. Prototype:function void insert (int index, queue_type item);

Q.insert (i, e) => Q = ‘{Q[0:i-1], e, Q[i,$]}

delete() Deletes the item at the specified index position. Prototype: function void delete (int index);

Q.delete (i) => Q = ‘{Q[0:i-1], Q[i+1,$]}

pop_front() Removes and returns the first element of the queue. Prototype: function queue_type pop_front();

e = Q.pop_front () => e = Q[0]; Q = Q[1,$]

pop_back() Removes and returns the last element of the queue. Prototype: function queue_type pop_back();

e = Q.pop_back () => e = Q[$]; Q = Q[0,$-1]

push_front() Inserts the given element at the front of the queue. Prototype: function void push_front (queue_type item);

Q.push_front (e) => Q = ‘{e, Q}

push_back() Inserts the given element at the end of the queue. Prototype: function void push_back (queue_type item);

Q.push_back (e) => Q = ‘{Q, e}


Queue Examplemodule queues ();

int q [$]; // declare the q

initialbegin: store_disp

// Push elements into the queueq.push_back(1);q.push_back(0);

// Display its contents$display("Size of queue = %0d", q.size());

// Delete the element of queue at index 1q.delete(1);

// Push to front of the queueq.push_front (0);

// Display all the contents in the queuefor (int i = 0; i < q.size(); i++)

$display("q[%0d] = %0d", i, q[i]);

end: store_disp

endmodule: queues


Lab 6: Queues

� Write a SystemVerilog program with specification as defined in lab6.sv

� The output will look as follows:# Loading work.lab6# run –all# Size of queue = 3# q[0] = 0# q[1] = 1# q[2] = 3# q -f


Associative Arrays

� Associative arrays are used when the size of the array is not known or the data is sparse.

� Syntax:data_type array_name [index_type];In other wordsvalue_type array_name [key_type];

� It implements a lookup table of the elements of its declared type.

� Data type used as an index serves as lookup key and imposes an order.

� Associative array do not have their storage allocated until it is used.


Index Types

� String Index Types� Ex: int a [string];a[“joe”] = 21;

� Integer Index Types� Ex: bit [1:0] a [int];a[5] = 2’b11;


Associative Array Methods

finds the entry whose index is greater/smaller than the given index.

next (<index>), prev (<index>)

assigns to the given index variable the value of the first/last (smallest/largest) index in the associative array. It returns 0 if the array is empty, and 1 otherwise.

first (<index>), last (<index>)

Returns 1 if element exists at index else 0

exists (<index>)

Index for delete optional. When specified used to delete given index else whole array.

delete(<index>)

Returns number of entriesnum()

UseFunction


Associative array methods - Examplemodule asoc_arry ();

int db [string]; // Define an associative arrayinitial begin: test

string s;db ["joe"] = 21; // store values at indexes of associative arraydb ["jill"] = 19;

// Display the size of the associative array $display("Size of hash = %0d", db.num());if (db.exists("jill")) // check if index exists and change valuebegin

db["jill"] = 25;end

// print the contents of associative arrayif (db.first(s))do begin

$display("Name = %s -- Age = %0d", s, db[s]); endwhile (db.next(s));

end: testendmodule: asoc_arry


Lab 7: Associative Arrays

1. Define an associate array named 'assoc' assoc has the following attributes:INDEX - Name of personVALUE - Age

2. Make the following entries into assocNAME AGE----------------John 25James 30Jane 24

3. Display the size of the hash using $display statement4. Check if name Jane exists in the associative array and if it does

change her age to 40.5. Print the contents of the associative array.

Procedural Blocks


Triggering sensitivity� @(<signal>) waits for an edge on <signal> before

executing the next statement� Edge-sensitive signal detection� @(posedge clk) – waits for a rising edge clock� @(negedge rstb) – waits for a falling edge on rs

� wait(<signal>) waits for a condition to become true before executing the next statement.� Level-sensitive signal detection� If the signal is already true, execution continues

without stopping


Initial Block� An initial block starts at time 0,

executes exactly once during a simulation, and then does not execute again.

� If there are multiple initial blocks, each block starts to execute concurrently at time 0.

� Each block finishes execution independently of other blocks.

� Multiple behavioral statements must be grouped, typically using begin and end.

Examplemodule stimulus;

reg a,b;

initial

begin

#5 a = 1’b1;

#25 b = 1’b0;

end

endmodule


Always Block

� The always block statement starts evaluating sensitivity list at time 0 and executes statements in the always block continuously in a looping fashion.

� This statement is used to model a block of activity that is repeated continuously.

Examplemodule clock_gen;

bit clock;

initial begin

clock = 1’b0;

forever #10 clock = ~clock;end

always @(posedge clk)

begin

<statements>;

end

endmodule


Final Blocks

� The final block is like an initial block, defining a procedural block of statements, except that it occurs at the end of simulation time and executes without delays.

� A final block is typically used to display statistical information about the simulation.

Examplefinal

begin

$display("Number of cycles

executed %d",$time/period);

$display("Final PC = %h",PC);

end


Lab 8: Procedural Blocks

Create a SystemVerilog module:1. Define an initial block such that it generates a clock clk time

period = 10nsNOTE: Need to initialize clock even though the bit data type is automatically done.

2. Create an always blocks that stores the value of signal 'clk' into queue 'q' at positive edge of the clock.

3. Increment 'counter' when always block is triggered4. When counter reaches 4 call $finish system call

Hint: Use if statement 5. Define a final block to print the size of 'q' at the end of simulation

Hint: Use final blocks

� Output:# Size of q = 4

Types of Assignment

BlockingNonblocking


Blocking Assignment

� The simulator completes a blocking assignment (=) in one pass [execution and assignment].

� Execution flow is blocked until a given blocking assignment is complete.

� If there is a time delay on a statement then the next statement will not be executed until this delay is over.

Exampleinitial

begin

a = 30;

#10;

a = 5;

c = #10 a;

b = 2;

end

// at time 0

a = 30

//at time 10

a = 5, b = x, c = x

// at time 20

a = 5, b = x, c = 5

// at time 20

a = 5, b = 2, c = 5


Nonblocking Assignment

� The simulator completes a non-blocking assignment (<=) in two passes.� Right-hand side of the

assignment is sampled immediately.

� Assignment to the left-hand side is postponed until other evaluations in a given simulation time step are complete.

Exampleinitial

begin

a = 30;

#10;

a <= 5;

c <= #10 a;

b <= 2;

end

// at time 0

a = 30

//at time 10

a = 5, b = 2, c = x

// at time 20

a = 5, b = 2, c = 30

Tasks and Functions


Tasks

return keyword is supported and terminates task at that point

ANSI style portlists

task automatic my_task( input int local_a,int local_b);

if (local_a == local_b)begin

my_task(local_a-1,local_b+1); return; // end ‘this’ copy of task

endglobal_a = local_a;global_b = local_b;

endtask

automatic tasks allocate memorydynamically at call time.

Implied begin…end

Default port direction is input

SystemVerilog makes a number of extensions to basic Verilog syntax.

Arguments can be ANYSV type, even structs, etc.

Full recursion is supported (automatic variables/arguments stored on stack)• Can do concurrent calls• Can do recursive calls


Task usage examples [1]Example of an automatic taskmodule task_reentry();

task automatic reentry();

int counter = 0;

counter++;counter++;

counter++;

counter++;

counter++;$display("Value of counter = %0d",

counter);

endtask

initial

begin

reentry();

reentry();reentry();

reentry();

end

endmodule: task_reentry

What will be the value of counter for each call to reentry()?

Example of a static taskmodule task_reentry();

task reentry();

int counter = 0;

counter++;counter++;

counter++;

counter++;

counter++;$display("Value of counter = %0d",

counter);

endtask

initial

begin

reentry();

reentry();reentry();

reentry();

end

endmodule: task_reentry

What will be the value of counter for each call to reentry()?


Task usage examples [2]

module task_function ();int i, j, z;

initialbegin

i = 5;j = 3;

endinitialbegin

#10;tsk (i, z, j);$display("Z = %0d, J = %0d", z, j); // prints Z = 50, J = 4

end

task tsk (input int t1, output int t2, inout int t3);t2 = 10 * t1;t3++;

endtask: tskendmodule


Functions

function automatic int factorial (int n);if (n==0) return(1); // factorial 0 is 1else return(factorial(n-1)*n);

endfunction

return(value) is supported and terminates function at that point

ANSI style portlists

automatic functions allocate memorydynamically at call time (full recursion).

Implied begin…end

Default port direction is input (also supports output)

Arguments and return type can be ANY SV type, even complex structs, etc.

function void inverta();a = !a

endfunction

reg a;

initialinverta(); // function called like a task

Return type of voidmeans no return value!

EndEnd

Recommended style (instead of writing a task)to guarantee a task executes with 0 delay.


Function usage examples

Example 2typedef enum {FALSE, TRUE} bool;

bool cache_range;

function bool is_cache_range ();

if (addr > 0 & addr < 10)

begincache_range = TRUE;

$display("addr in cache range = %d", addr);

return TRUE;

endelse begin

cache_range = FALSE;

return FALSE;end

endfunction

Example 1function void show_packet();

$display("==================");$display("Packet Type = %s",

context_name);$display("Address = %h", addr);$display("Data = %h", data);

$display("===================");endfunction


Task and Functions Usage - Summary

� Tasks� Tasks can enable other tasks and functions� Tasks may execute in non-zero simulation time.� Tasks may have zero or more arguments of type input, output

and inout.� Functions

� Function can enable other functions only. Task cannot be called from functions.

� Functions should execute in zero simulation time.� Functions have only one return value but SystemVerilog also

allows functions to have input, output or inout types.� Both tasks and functions support passing arguments by

reference. By default arguments are passed by value. [Pass by reference not supported in Modelsim 6.1]


Task and function argument passing

� Passing by value is the default mechanism for passing arguments.

� Copies arguments passed into subroutine area.

� Changes to arguments in subroutine are not visible outside.

� When defined as automatic, each copy retains a local copy of argument.

Examplefunction int val

(byte m [3:0]);

<function body>;

endfunction

// a local copy of ‘m’ is

// created when ‘val’ is

// called.


Default argument values – Tasks/Functions

� SV allows a subroutine declaration to specify default value for each argument.

� When subroutine is called, arguments with default values can be omitted from the call and corresponding default values are used.

� BKM: Default arguments should be optional arguments and should be the final set of arguments.

Exampletask read (int j =0,

int k,int data = 1);

endtask

// task can be called using

// following default arguments

read (, 5);

// equivalent: read (0, 5, 1)

read (2, 5);

// equivalent: read (2, 5, 1)

read ();

// error since k has no default

// value


Lab 9a

� Create a SystemVerilog module as described below:

1. Define a queue 'q' of string type.2. Define a named initial block "store_info"3. Store the following values into the queue

1. index =0, str = "Intel Chandler"2. index =1, str = "Intel Folsom"

4. Display the size of the queue.5. Define a function named "change_str" which does the following:

1. Takes queue and index value as input2. changes the value of str stored in queue at index 1 to "Intel

Ireland" from "Intel Folsom“. 3. returns the value of 1 indicating success.


Lab 9b6. Define a task named “show" which does the following:

1. Takes queue and return value from "change_str" as inputs2. The default inital value [task input argument: ret_value] shall be

set to 0.3. When the return value from "change_str" function is 1, prints the

elements stored in the queue using the following format:q[%0d] = %s"

7. Notes: "change_str" and “show" are called from named initial block "store_info".

� Output:# Loading work.lab9# run –all# Size of storage q = 2# q[0] = Intel Chandler# q[1] = Intel Ireland# q -f

Hierarchy

Who comes first


Modules

The basic hardware unit in Verilog.Hierarchy of design Ports represent communication

ModuleInputs

Outputs

Inout


Ports

ConnectionsDirection – input, output, inoutType – wire, bit, logic, user-defined, etc.

Examples:input bit[3:0] x, y, z;

input bit w[3:0];

output logic q;

inout logic s;

input int x;

output reg r;


Module syntax

module x (port_list);module_body

endmodule : x

Instantiationx x1 (port_binding_list);

Examplemodule cpu(inout logic[63:0] data, output logic[63:0] addr, output logic w_or_rb);initial begin : place_holder$display(“A NOTHING CPU”);

end : place_holderendmodule : cpu

// Error pronecpu cpu_inst1(addr, data, w_or_rb);// Bettercpu cpu_inst2(.addr(addr),

.data(data),

.w_or_rb(w_or_rb));

// Newercpu cpu_inst3( .* );


Parameters

Generic parameters (ala VHDL generics)Elaboration time constantsSeparate “ports” on a moduleExamplemodule xyz

#(parameter int width = 8)(input x[width-1:0], output y));assign y[width-1:0] = x[width-1:0]^ 8’hAE;

endmodulexyz #(.width(14)) xyz1 (.x(inp), .y(outp));


Multiple drivers

� Most nets have only one driver� Nets with multiple drivers need to have a

resolution function� In SystemVerilog there is a wire type that

includes a resolution functionExamplewire x;dut dut1(.outp(x));dut dut2(.outp(x));


InterfacesGreat coding efficiency can be achieved by modeling the blocks of a system at different levels of abstraction, behavioral, rtl, gate, etc. In Verilog, the I/O between these blocks has always remained at the lowest “wire” level. High-performance system-level simulation requires the abstraction of inter-block communication.

MMU MEM

data

addr

rw_

ena

interface

module mmu(d, a, rw_, en);output [15:0] a;output rw_, en;inout [7:0] d;. . .

endmodule

module mem(d, a, rw_, en);input [15:0] a;input rw_, en;inout [7:0] d;. . .

endmodule

module system;wire [7:0] data;wire [15:0] addr;wire ena, rw_;

mmu U1 (data, addr, rw_, ena);mem U2 (data, addr, rw_, ena);

endmodule

Traditional Verilog

interface interf;logic [7:0] data;logic [15:0] addr;logic ena, rw_;

endinterface

module mmu(interf io);io.addr <= ad; . . .

endmodule

module mem(interf io);adr = io.addr;

. . .endmodule

module system;interf i1;mmu U1 (i1);mem U2 (i1);

endmodule

SystemVerilogAt it’s simplest an interface islike a modulefor ports/wires

ad adr


IO Abstraction

intf.a = 0; if ( intf.a == 1)…

a reg a;

source sinkinterface intf

intf.wrt_a(0); if (intf.rd_a() == 1)a reg a;

source sinkinterface intf

task wrt_a();task rd_a();

a = 0;

if ( a == 1)…

aa a

source sink

reg a; Traditional Verilog approach• Simple netlist-level IO• source/sink can be abstracted

but IO must stay at low level• IO operations are cumbersome

Simple “bundle” interface• All accesses are through interface• Simplifies source/sink declarations

Enhanced interface with methods• source/sink only call methods• source/sink don’t see low-level

“details” like variables/structure, etc.• Easy to swap interface abstractions

without any effect on source/sink


Interface Characteristics

• Interfaces bring abstraction-level enhancements to ports, not just internals.

• An interface may contain any legal SystemVerilog code except module definitions and/or instances. This includes tasks, functions, initial/always blocks, parameters, etc.

• Bus timing, pipelining, etc. may be captured in an interface rather than the connecting modules.

• Interfaces are defined once and used widely, so it simplifies design. e.g. Changing a bus spec (add a new signal?) means editing the interface only.

• Interfaces are synthesizable.


Interface in hierarchy

� Interfaces appear as normal module instantiations in design hierarchy.

� At the moment, interfaces cannot be instantiated in VHDL blocks.

Interface instances interface name: bfm_interface

Instantiated twice: bi1, bi2


modport

� Different users of interface need different views� Master/Slave

� Restrict access to internal interface signals� Protect

implementation signals from corruption

Exampleinterface i2;wire a, b, c, d;modport master (input a, b,

output c, d);modport slave (output a, b,

input c, d);endinterface : i2

module m (i2.master i);…

endmodule: m

module s (i2.slave i);…

endmodule: s

module top();i2 i();

m u1(.i(i.master));s u2(.i(i.slave));

endmodule: top


Lab 10

Create modules moda and modb. moda has an input named a, and an output

named bmodb has an input named b, and an output

named aUse an interface to connect


Clocking blocks

Synchronous blocks can have race conditions when all trying to evaluate blocks in same time step

Clocking blocks capture timing and synchronization requirements


Clocking block syntax

clocking block_name clocking_event;item list;

endclocking : block_name

clocking bus @(posedge clock1);default input #10ns output #2ns;input data, ready,

enable=top.mem1.enable;output negedge ack;input #1 addr;

endclocking


Program Blocks

A program block is similar to a module. It is used for testbench code.

program helloWorld();initialbegin: hello

$display("Hello World");end

initialbegin: there

$display(“Hello There”);end

endprogram: helloWorld


Program Blocks

Programs can be instantiated inside modules, but not the other way around.

Program blocks may contain one or more initial blocks, but may not contain always, UDPs, modules, interfaces, or other programs.

Programs may be explicitly exited using the $exit task.

When all program blocks complete the simulation ends.

Day Two

Classes

SystemVerilog and Object Oriented Programming

Testbench Only


Object Oriented Primer

A Class is a description of some group of things that have something in common.

Objects are individual instances of “classes”.� Example: A class might be “Automobile”. Instances of the

“Automobile” class might be “Joe’s car”, “Bob’s car”, “Sally’s truck”, etc.

Objects/Classes have: � Data

� Color, speed, direction, etc.� Operations/Methods

� Start, stop, increaseSpeed, turn, etc.Encapsulation:

� Encapsulate implementation details internal to the object/class.


Classes

Inheritance: (is-a relationship)� Allows users to extend existing classes, making minor

modifications. Extending the “Automobile” class example, users might create subclasses for “sedan”, “truck”, “van”, etc. The “van” class might also have a “minivan” subclass. Etc. In these cases, the subclass IS-A superclass. i.e. a “sedan” is a “Automobile”.

� When using inheritance, the sub-class “inherits” all the parents public/protected data properties and methods. It is allowed to override them, or use them as-is.

Composition: (has-a relationship)� Composition is used for the case where one object HAS-A

instance of another class. For example, an “Automobile”class might have 4 instances of a “wheel” class. In this case, a wheel is not an “Automobile”, so inheritance should not be used.


Classes

Polymorphism:� Most common definition of polymorphism is the ability of

the language to process objects differently depending on their data type or class. SystemVerilog can only process objects differently depending on their class.


Class Format

class classname [extends superclass];

property declarations;

constructor;

methods;

endclass: myPacket


Example Classclass myPacket extends BasePacket; // inheritance

byte data[$];bit [3:0] command;

function new();command = IDLE;data = ‘{1,2,3,4};

endfunction: new

virtual task myTask(input byte a, output byte b);#10;b = a + 5;

endtask: myTask;

virtual function integer myFunc(int b);return(b – 3);

endfunction: myFuncendclass: myPacket


Referencing Properties and Methods

Instance data properties and methods may be referenced/called using the “.” operator.

c = new;c.property1 = 10;c.property2 = 11;c.task1();c.function1();


Constructors

Example constructorfunction new();

command = IDLE;data = {1,2,3,4};

endfunction: new

// Creating an instance invokes the constructor:myInstance = new;

Constructors may take arguments.function new(int a = 0, bit[12:0] addr = 0);

…endfunction: new

When extending a class constructor, call super.new().function new();

super.new();…

endfunction: new

Only one constructor per class allowed.


this

The special variable this is a predefined object handle for the current object instance. It is optional, since the current instance is assumed if no variable is specified.

class myPacket extends BasePacket;int x, y, z;

…

virtual function integer myFunc();x = y + z;// Equivalent: this.x = this.y + this.z;

myOtherMethod();// Equivalent to: this.myOtherMethod();

endfunction: myFuncendclass: myPacket


Static PropertiesStatic properties/data members are “static” to

all instances of the class. This means that all instances share the same value of this variable. If one instance changes the value, it changes the value for all instances.

class StaticExample;static int staticProperty = 0;

virtual function void showStaticProperty();$display(“Current value: %d”,staticProperty);

endfunction: showStaticProperty

virtual function void setStaticProperty(int val);staticProperty = val;

endfunction: setStaticPropertyendclass: StaticExample


Static Methods

Static methods do not require an instance of the class to operate on. Static methods may only modify static properties. To invoke a static method, use Classname::methodName

class StaticExample;static int staticProperty = 0;

static function void staticMethod();…

endfunction: staticMethodendclass: StaticExample

StaticExample::staticMethod();


Polymorphism

Instances of subclasses may be assigned to variables declared of the superclass type.

This is useful for cases where the general algorithm is the same for all the subclasses, but only a few details need to change.

If the subclass overrides a method specified in the superclass, the method defined in the class of the object instance is called.

class BaseClass;virtual function in myFunc(int b);

return(b + 10);endfunction myFunc

endclass: BaseClassclass myFirstClass extends BaseClass;

virtual function int myFunc(int b);return(b – 3);

endfunction: myFuncendclass: myFirstClassclass mySecondClass extends BaseClass;

virtual function int myFunc(int b);return(b + 3);

endfunction: myFuncendclass: mySecondClass

BaseClass bc;

// Returns an instance myFirstClassbc = getFirstClassInstance();$display(“What do I print? %d”

,bc.myFunc(6));

// Returns an instance mySecondClassbc = getSecondClassInstance();$display(“What do I print? %d”

,bc.myFunc(6));


Data Hiding and Encapsulation

To make data members visible only to the class, use the local keyword.

class myPacket extends BasePacket;local int x;

To make data members visible only to the class, or any subclasses, use the protected keyword.

class myPacket extends BasePacket;protected int x;


Constant Class Properties

The const keyword may be used to make class properties unchangeable. const constants are different from d̀efine constants because the initial value may be

determined at runtime, and may be different per class instance.class myPacket extends BasePacket;

const int size; // Assignment of constant value in // declaration makes it constant // to all instances.

function new(int id);size = id * 4096; // Single assignment in

// constructor OK

…


Abstract Classes

The virtual keyword may be used on a class to make the class “abstract”. An abstract class may not be instantiated. Users must subclass the abstract class to create instances of the class.virtual class BasePacket;

…


Typedef Class and Forward References

Sometimes it is necessary to use a class before it has been defined. To do this, you can use a typedefforward reference, then later define the class. Example:

typedef class C2; // Forward declaration of C2class C1;

C2 c2Instance;…

endclass: C1class C2;

C1 c1Instance;…

endclass: C2


Lab 11a: ClassesCreate an “Xaction” class. The Xaction class should have the followingProperties:

byte data[$]; // Queue of bytesint length; // Length in bytes

Methods:// Sets data to value passed and // length to the size of queue passed.setData(byte d[$]);

// Returns formatted representation of // xaction. Format should be:// Len=X, Data=0xXXXXXXXXstring toString();

Hint: $sformat(str,"Len=%d, DATA=0x%h",length,data);

Using your new class, run the following test code.Xaction x;

x = new;x.setData(‘{1,2,3,4,5,6,7,8});$display(“%s”,x.toString());


Lab 11b: ClassesModify lab10a and create a subclass of the Xaction class that has the following

property added:int iws; // Initiator wait states

Add a task to the class that waits for the number of time steps specified in iws:// Wait IWS time stepsstall();

Override the toString() method, add printing the iws value. Be sure to use super.toString, and not reimplement the toString of the parent class:

// Len=X, Data=0xXXXXXXXX, IWS=X

Execute the following testcode.Xaction x;SubXaction s;

s = new;s.iws = 10;$display(“current time = %t”,$time);s.stall();$display(“current time = %t”,$time);

x = s;x.setData(’{5,6,7,8});$display(“%s”,x.toString());


Virtual Interfaces

� Classes cannot have modules or interfaces, need a specialized mechanism

� Virtual interfaces provide a mechanism for separating test programs/BFM models from the actual signals.

� Virtual interfaces let BFM models manipulate virtual set of signals instead of actual RTL signals.

� Virtual interface is a variable that represents an interface instance.

� Syntax: virtual <interface name>

<variable name>;


Virtual Interfaces Exampleclass BFM;

virtual Bus bus;

Xaction xaction;

function new (virtual Bus b);

// need to initialize virtual interface// in constructor

bus = b;

xaction = new;

endfunction

task req_bus();

@(posedge bus.clk);

bus.req <= 1'b1;

$display("Req = %b @ %0t", bus.req, $time);

endtask: req_bus

endclass: BFM

// interface

// definitioninterface Bus (input logic clk);

bit req;

bit grant;

logic [7:0] addr;

logic [7:0] data;

endinterface: Bus

// testbench

// interface instance

Bus infc_b (clk);

// dut instance dut dut1 (infc_b, clk);

// class instance BFM mybfm =

new (infc_b);

Random Constraints

How to decide how random to be


Random data sources

Random exercise of stimulus allows easy cases to be done easily

Ability to “tune” random stimulus usually gives more coverage with less work (be careful)

Save the impossible cases until the Design Under Test (DUT) is healthier

Works hand-in-hand with functional coverage


Simplest randomness

$urandom system tasks$urandom() is SV, thread stable, deterministic $urandom returns unsigned 32-bit integersProcedural call can be inserted wherever

needed


More sophisticated mechanisms

Random variables (rand modifier – classes only)Must be properties of a class, except for some explicit randomizationSelect new random value each time “.randomize()” is called

Example:class x;

rand int a, b, c;endclass : xx x_inst = new;initialbegin : random_loop

forever @(posedge clk) x_inst.randomize();end : random_loop


What’s ‘randc’ for?

Exhaustive permutations of a variable‘c’ is for “cyclic”, every value of the variable will

be reached before any value is duplicatedCaution… special solver ordering for randc


Constraints

Set of Boolean algebraic expressionsRelationships between random variables and:

Other random variablesNon-random state variables

Example:constraint a_le_b { a <= b; }constraint c_eq_10 {c == 10;}constraint b_in_range { b >= 2 && b <= 8; }constraint all_gt_0 {a > 0; b > 0; c > 0;}

How many permutations are now possible?


Constraints

Restrict range of possible valuesCan use state variables to restrict range of

random variablesExample:int x[7] = ’{3,5,6,27,10,42,1};int z = ’hff, w = 10;constraint c_within_set_of_x { c inside x; }constraint b_between_w_z { b <= z && b >= w; }


Conflicting constraintsWhat happens when you impose constraints

that conflict in some way?Example:

constraint x_gt_y { x > y; }

constraint y_gt_z { y > z; }constraint z_gt_x { z > x; }

…

if ( x_inst.randomize() == 0 ) // Solver errorbegin

…end

Modelsim cmdline setting-solvefaildebug


Constraint operators

Any Verilog boolean expressioni.e. x < y+b-c*10>>20

Other constraint operationsset membership within

implication -> or if…else…iterative constraint foreach

variable ordering solve … before …functions func_x()


Implication constraint

Uses one boolean to decide if another constraint must hold(trans_size == SMALL) -> (length < 10)

(trans_size == MED) -> (length >= 10 && length <= 100)

(trans_size == LARGE) -> (length > 100)

Advanced note:a -> b is equivalent to !a || b


Loop/array constraints

Constrain every element of an array in some fashion, including reference to other elements of array

constraint c1 { foreach ( A[i] )

A[i] inside {2, 4, 6, 8, 10}; }

constraint c2 { foreach ( A[k] )

(k < A.size-1) -> A[k+1] > A[k];

}


Arguments to .randomize()

� Normal form of .randomize()� No arguments, randomize class members according to

declaration modifiers

� Optional arguments� Specify the variables which are random� Can make ‘rand’ override declaration type for this call� Declares entire set of random variables for this run of

Constraint Solver� ‘null’ argument forces checking constraints only� Cannot change ‘randc’ to ‘rand’


.randomize with {}

� Specify inline constraints that are added to constraint set to solve

trans.randomize() with { x < 100; z > buzz; };


Distribution Constraints� Operators: := :/ dist� Example:constraint twsConstraint{

tws dist {

[0:2] :/ 10,[3:9] :/ 1,[10:50] :/ 9

};}constraint distConstraint{

cmd dist {

mem_write := 10,mem_read := 5,lrw := 1,lrrww := 1,io_read := 1,io_write := 1,idle := 1

};}


Putting it all togethermodule test_rand;typedef enum {SM, MED, LRG} trans_len;class transaction {

rand bit [19:0] addr;rand trans_len len;rand bit [3:0] byte_len;rand bit wr_or_rd_b;

constraint c1 { wr_or_rd_b -> len != LRG; }constraint c2 { (len == SM) -> (byte_len <= 4); }constraint c3 { (len == MED) -> (byte_len > 4 && byte_len <= 8);}constraint c4 { (len == LRG) -> (byte_len > 8); }// Mem above 16-bit is write-only IO devicesconstraint c5 { (!wr_or_rd_b) -> (addr[19:16] != 0); }

virtual function string toString() return sformat(“%5H: %s %d bytes”, addr, (wr_or_rd_b ? “WR” :

“RD”), byte_len);endfunction : toString

endclass : transaction<CONTINUED>


Putting it all together (cont)transaction trans = new();intialbegin : test_bodyint counter = 0;repeat (20) begin : rand_genif (trans.randomize() == 0) begin$display(“ERROR: Random constraints

conflict”);$finish;

end$display(“%d: %s”, counter++, trans.toString());end : rand_gen

end : test_body

endmodule : test_rand


Lab 12: Random Constraints

Modify the Xaction class created in lab11 and make all properties rand.

1. Add a rand property named size, with the following enumerated values: SMALL, MEDIUM, LARGE.

2. Add a distribution constraint that make the size: SMALL 70%, MEDIUM 20%, LARGE 10%.

3. Add a constraint that sets the length based on the size property:

SMALL : (length <= 10)MEDIUM : (length >10) && (length <=20)LARGE : (length > 20) && (length < 100)(Note: Add a constraint saying the length must be > 0)

4. Write a loop that calls randomize() 40 times, printing the Xaction after each randomize() call.


Packages

� A mechanism for sharing parameters, data, types, tasks, functions, classes, sequences, and properties among modules, interfaces and programs


Package Search Order Rules

The importing identifiers become directly visible in the importing scope:- c

import p::c

if ( ! c ) …

All declarations inside package p become potentially directly visible in the importing scope:- c, BOOL, FALSE, TRUE

import p::*;

y = FALSE;

A qualified package identifier is visible in any scope

u = p::c, y = p::TRUE

package p;

typedef enum {FALSE, TRUE} BOOL;

BOOL c = TRUE;

endpackage


Package Example

� keyword� package … endpackage

Example:package p;

class Data;int a;int b;

endclass

typedef enum {FALSE, TRUE} BOOL;

endpackage : p

module top;

import p::*;

BOOL b = TRUE;

endmodule

ORmodule top;

p::BOOL b = p::TRUE;

endmodule


Lab 13: Packages

Create two packages which contains an int C and C is initialized with two different values.

Write a top level module that print out both C value

System Tasks


Display

� $display – printf-ish, with “\n” implied� $display (format_string, arguments);

� $write – printf-ish ($display w/out newline)� $sformat – print formatted string (ala sprintf)� $monitor – Implicit task to call $display any time

arguments change, only one $monitor active


Time

� $time – Returns 64-bit time normalized to unit timescale, most common for error messages

� $realtime – floating point scaled to timescale

� $stime – least significant 32-bits of time


Simulation Control

$finish – end simulation (quit simulator), final blocks$stop – halt simulation$exit – quit execution of program block (SV-only)

Exampleinitial

#10000 $finish();

initial

@(posedge all_bfms_done) $finish();


File I/O

integer fd = $fopen(string filename, string mode)char c = $fgetc(int fd);int code = $ungetc(char c, int fd);integer code = $fgets(string str, int fd);integer code = $fscanf(int fd, FORMAT, args);integer code = $sscanf(string str, FORMAT, args);Example

string buf_s;in_fd = $fopen(“input_file”, “r”);out_fd = $fopen(“output_file”, “w”); chars_read = $fgets(buf_s, in_fd);if (chars_read == 0)

begin$display(“End of file”);$finish();

endif (2==$sscanf(buf_s, "%x %x", hexStartAddr, hexEndAddr) )

begin$display(“Address Range: %8x -> %8x”, hexStartAddr, hexEndAddr);

end


File I/O

$fclose $fopen$fdisplay $fstrobe$fdisplayb $fstrobeb$fdisplayh $fstrobeh$fdisplayo $fstrobeo$fgetc $ungetc$fflush $ferror$fgets $rewind$fmonitor $fwrite$fmonitorb $fwriteb$fmonitorh $fwriteh$fmonitoro $fwriteo$readmemb $readmemh$swrite $swriteb$swriteo $swriteh$sformat $sdf_annotate$fscanf $sscanf$fread $ftell$fseek


Random functions

$random

$dist_chi_square $dist_erlang

$dist_exponential $dist_normal

$dist_poisson $dist_t

$dist_uniform


Named blocks

� Blocks can be provided names. By providing blocks with names provides the following advantages:� Declaration of local

variables.� Named blocks are part of

the design hierarchy.� Local variables declared

can be accessed through hierarchical referencing.

Example…

always @(CK or D)

begin : latch_counter

int count;

if (CK)

count = count + 1;

begin

O = D ;

end

end : latch_counter

…

Threads


Sequential Blocks� There is the difference

between a sequential and a concurrent block:� Simulator executes

statements in a sequential block in sequence

� It finishes the current statement, then begins the next

� You always know the order in which it actually executes the statements

� The simulator exits the block after finishing the last statement

Examplebegin

#5 a = 1;

#5 a = 2;

#5 a = 3;

end


Concurrent Blocks

� The simulator executes statements in a concurrent block in parallel� It starts executing all

statements simultaneously� You can not know the order in

which it actually executes statements scheduled for the same simulation time

� The simulator exits the block after finishing the latest statement.

� A return statement in the context of fork..join is illegal.

Examplefork

begin

$display( "First Block\n" );

# 20ns;

end

begin

$display( "Second Block\n" );

@eventA;

end

join


Dynamic Processes

Inspired by the need for software verification environments to dynamically start and stop threads, SystemVerilog defines 2 new special cases of fork…join with associated keywords join_any & join_none

fork………

join_any // any block finished

beginfork

…join_none // no waiting at all@(sig1);

end

NOTEChild processes spawned by

a fork…join_none do not start to execute until the parent

process hits a blocking statement

join_any join_none

other blocks continue as dynamic threads


Process Control – Wait Fork

With Dynamic processes SystemVerilog needed to provide more global detection that spawned processes have completed.

The wait fork statement is used to ensure that all child processes (spawned bythe process where it is called) have completed execution.

beginfork

task1();task2();

join_any // continue when either task completes

forktask3();task4();

join_none // continue regardless

wait fork; // block until tasks 1-4 completeend

Q6.1


Process Control – Disable Fork

The disable fork statement terminates all active child processes of the process where it is called. Termination is recursive, in other words it terminates child processes, grandchild processes, etc.

// 2 child tasks spawned in parallel, first to finish triggers join_any

// Kills the slower task (including any grandchild processes and so on)

task run_tests;fork

simul_test1;simul_test2;

joinendtask

task test_with_timeout;fork

run_tests();timeout( 1000 );

join_anydisable fork;

endtask

Q6.1


Events Trigger Types [1]

� Triggering an event� Named events are triggered

using -> operator.� Triggering an event

unblocks all processes currently waiting on the event.

� These events are such that trigger state cannot be observed but only their effect.

� Event can be visualized in wave window.

module event_testing ();

event a, b;

bit clk;

always @(posedge clk) -> a;

always @(negedge clk) -> b;

initial

begin

clk = 1'b0;

forever #10 clk = !clk ;

end

endmodule


Events Trigger Types [2]

� Nonblocking event trigger� They are triggered using

->> operator.� The statement executes

without blocking and it creates a nonblockingassign update event in the time in which the event occurs.

� The effect of this event is felt during the nonblockingassignment region of a simulation cycle.

Examplealways @(posedge clk)

begin

if (counter == 2)

->> a;

counter++;

end

initial

begin

forever @(a)

$display("event a

triggered @ %0t, $time);

end


Waiting for an event

� @ is used to wait for an event.

� The @ operator blocks the calling process until the given event is triggered.

Examplemodule event_testing ();

event a, b, c;

bit clk;

always @(posedge clk) -> a;

always @(negedge clk) -> b;

always @(a or b)

-> c;

initial

begin

clk = 1'b0;

forever #10 clk = !clk ;

end

endmodule


Event Sequencing: wait_order()

� wait_order construct suspends the calling process until all specified events are triggered in the given order [left to right].

� If any events are triggered out of order then it causes a fail of the operation.

Examplebit success;

wait_order (a, b, c)

success = 1;

else

success = 0;

// event must occur in the

// following order

// ->a ->b ->c if not it fails.


Event Variables [1]

� Merging Events� When one event variable

is assigned to another, both merge into one event variable.

� Executing -> on either one of the events affects processes waiting on either event variable.

Exampleevent a, b;

a = b;-> a; // also triggers b

-> b; // also triggers a


Event Variables [2]

� Reclaiming Events� When an event variable

is assigned the special null value, the association between the event variable and the underlying synchronization queue is broken.

Exampleevent E1 = null;


Event Variables [3]

� Event Comparison� Event variables can be

compared against other event variables or the special value null.

� Equality (==) with another event or with null.

� Inequality (!=) with another event or with null.

Exampleevent E1, E2;

if ( E1 ) // same as if ( E1 != null )

E1 = E2;

if ( E1 == E2 )

$display( "E1 and E2 are the

same event" );


Semaphores

� Can be described as counters used to control access to shared resources by multiple processes [threads].

Printmanager

Printer1[1]

Printer2[1]

Printer3[1]

3 keys2 keys

Printer1[0]


Semaphore Methods

� Semaphore provides following built-in methods:

Try to get one or more keys without blocking.

try_get()

Obtain one or more keys.get()

Return one or more keys back.

put()

Create a semaphore with specified number of keys.

new()

UseMethod


Semaphore example

Output:# initial1 takes 1 key at 1

# initial1 returns 1 key at 7

# inital2 takes 2 keys at 7

# inital2 returns 1 key at 12

# initial1 takes 1 key at 12

# q -f

initial begin:init2#5 spr.get(2);$display(" inital2 takes 2

keys at %0t",$time);#5 spr.put(1);$display(" inital2 returns

1 key at %0t",$time);endendmodule: semaphore_test

module semaphore_test ();semaphore spr = new(2);

initial begin:init1#1 spr.get(1);$display("initial1 takes

1 key at %0t", $time); #6 spr.put(1);$display("initial1 returns

1 key at %0t",$time);#1 spr.get(1);$display("initial1 takes 1

key at %0t", $time); end


Mailboxes

� Mailbox is a communication mechanism that allows messages to be exchanged between different processes.

Process 2Process 1


Mailbox Types

� Mailboxes can be classified as:� Unbounded mailboxes

� No restrictions placed on size of mailbox.� put() will never block.� Ex: mailbox m = new ();

� Bounded mailboxes� Number of entries is determined when the mailbox is

created.� Bound value should be positive.� put() will be blocked if the mailbox is full.� Ex: mailbox m = new (5); // mailbox of depth = 5


Mailbox Methods

� Messages are placed in strict FIFO order. This does not guarantee order of arrival but that the arrival order shall be preserved.

� Mailboxes provides following built-in methods:

Copies a message from mailbox without actually removing it.

peek()

Try to place a message in mailbox without blocking.Useful only for bounded mailboxes.

try_put()

Try to retrieve a message from the mailbox without blocking.

try_get()/try_peek()

Retrieve a message from mailbox.get()

Place a message in a mailbox.put()

Create a new mailbox.new()

UseMethod


Mailbox examplemb_size = mb.num();for (int i=0; i<mb_size; i++)begin: dis_l

Xaction d_x;mb.get(d_x);$display("Addr = %h",

d_x.addr);end: dis_l

end: tendmodule: mailbox_ex

module mailbox_ex ();class Xaction;

rand bit [2:0] addr;endclasstypedef mailbox #(Xaction) mbx;mbx mb = new ();

initial begin: tXaction xaction;int mb_size;

for (int i=0; i<5; i++)beginxaction = new;xaction.addr = 3’b111;$display("BEFORE:: Addr = %h",

xaction.addr);mb.put(xaction);

end


BACKUP


foreach (Not in ModelSim 6.1) {BACKUP}

Implicit loop variable(s), multiple dimensions, any array type

int arr_x[];typedef int arr_joe[7:0][3:8]arr_joe arr_y[$];int arr_z[0:3*width][8*num-1:0];

initial begin

arr_x = new[10];foreach (arr_x[i]) statementforeach (arr_y[m,n,p]) statementforeach (arr_z[i,j]) statement

end


‘unique’ and ‘priority’ modifiers {BACKUP}

Modifiers on if and case/casex/casez selection expressions

‘unique’ - no more than one branch may be true for each evaluation, simulator errors if this happens

‘priority’ - order of evaluation is importantBoth modifiers require that if no fall-through

else/default statement is available, and no branch is true, an error is generated


Lab 5: CRC}


Lab 5: CRC (cont) {BACKUP}

Implement the CRC algorithm shown in the previous foil.

The operators << (left shift) and ^ (xor) will be needed.

Process the bitstream given in the lab file and report the CRC.


Constraint Guards {BACKUP}

Guards prevent the application of constraints, similar to implication, but remove the constraint from consideration of the constraint solver

Use the same implication operator, just using state variables

(!global_reset_state && cmd) -> (cmd_type != IDLE)

Can even test obj pointers for null(a != null && a.x > 10) ->

(y < 100 && y > a.x)


std::randomize() {BACKUP}

� Procedural invocation of constraint solver� Any variables can be the random variables� “with” block for constraints� Normal .randomize() cannot include variables

outside scope of class


Disabling rand/constraints {BACKUP}

� rand_mode – method to toggle the “rand”attribute off on a class variable

� constraint_mode – method to toggle the application of a named constraint


Random Stability {BACKUP}

� SV has thread random stability

IntroToSV_orgi

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Transcript of IntroToSV_orgi