SystemVerilog_veriflcation system verilog concepts for digital vlsi.ppt

An Introduction to SystemVerilog

This Presentation will…  Define what is “SystemVerilog”  Provide an overview of the major features in “SystemVerilog”  How it’s different from other languages Prime goal is to make you understand the significance of SystemVerilog

References Websources: 1. www.systemverilog.org 2. www.asic-world.com/systemverilog/index.html 3. http://svug.org/ Books : 1. Writing Testbenches using SystemVerilog - Janick Bergeron 2. Verification Methodology Manual - Janick Bergeron 3. SystemVerilog For Verification - Chris Spear

 SystemVerilog is a hardware description and Verification language(HDVL)  SystemVerilog is an extensive set of enhancements to IEEE 1364 Verilog-2001 standards  It has features inherited from Verilog HDL,VHDL,C,C++  Adds extended features to verilog What is SystemVerilog?

 System verilog is the superset of verilog  It supports all features of verilog plus add on features  It’s a super verilog  additional features of system verilog will be discussed What is SystemVerilog?

System Verilog Assertions OOP support Constrained Randomization New data types ie,logic Coverage support Easy c model integration Narrow gap b/w design & verification engineer Why SystemVerilog?

 Design entry  Module level verification  Module level design  Gate level simulations  System level verification  Unified language to span almost the entire SoC design flow Verilog System Verilog SystemVerilog Intent

Relaxed data type rules  Strict about usage of wire & reg data type  Variable types are 4 state – 0,1,X,Z  Logic data type can be used so no need to worry about reg & wire  2 state data type added – 0, 1 state  2 state variable can be used in test benches,where X,Z are not required  2 state variable in RTL model may enable simulators to be more efficient Verilog System Verilog

Memory Management  Memories in verilog are static in nature Example :-reg[7:0] X[0:127]; 128 bytes of memory  Memories are dynamic in nature  Allocated at runtime  Better memory management ie,queues Example:Logic[3:0] length[$]; an empty queue with an unbounded size of logic data type Verilog System Verilog

Complexity  For complex designs large number of RTL code is required  Increase in verification code to test these designs  Extra time  Less RTL & verification code  Less code hence less no. of bugs  Readable  Higher level of abstraction due to algorithmic nature(inherited from C++) Verilog System Verilog

Hardware specific procedures It uses the “always” procedure to represent  Sequential logic  Combinational logic  Latched logic It uses three new procedures  always_ff - sequential logic  always_comb - combinational logic  always_latch - latched logic Verilog System Verilog

Port connections  Ports are connected using either named instance or positional instance  Ports are connected using Design DUT(.*);which means connect all port to variables or nets with the same name as the ports Verilog System Verilog

Synthesis support Extensive support for verilog-2001 in simulation and synthesis  Synthesis tool support for system verilog is limited Verilog System Verilog “This is a major drawback which is restricting people to accept SystemVerilog as a Design language”

System Verilog Concepts reg r; // 4-state Verilog-2001 logic w; // 4-valued logic, see below bit b; // 2-state bit 0 or 1 integer i; // 4-state, 32-bits, signed Verilog-2001 byte b8; // 8 bit signed integer int i; // 2-state, 32-bit signed integer shortint s;// 2-state, 16-bit signed integer longint l; // 2-state, 64-bit signed integer Explicit 2-state variables allow compiler optimizations to improve performance logic is has single driver (procedural assignments or a continuous assignment), can replace reg and single driver wire. (Equivalent to “std_ulogic” in VHDL) Bit subs allowed Data types :

System Verilog Concepts join fork Fork/join Initial Begin Clk =0; #5 Fork #5 a = 0; #10 b = 0; Join Clk= 1; end Clk becomes 1 at t=15

System Verilog Concepts Join_any fork Fork/join_any Clk becomes 1 at t=10 Initial Begin Clk =0; #5 Fork #5 a = 0; #10 b = 0; Join_any Clk= 1; end

System Verilog Concepts Join_none fork Fork/join_none Clk becomes 1 at t=5 Initial Begin Clk =0; #5 Fork #5 a = 0; #10 b = 0; Join_none Clk= 1; end

System Verilog Concepts Final block  Executes at the end of simulation  It can not have delays  Used in verification to print simulation results, such as error report, code coverage reports

System Verilog Concepts Tasks & Functions  No begin end required  Return can be used in task  Function return values can have a “void return type”  Functions can have any number of inputs,outputs and inouts including none

System Verilog Concepts DPI(Direct Programming interface )  DPI’s are used to call C, C++, System C functions  System verilog has a built in C interface  Simple to used as compared to PLI’s  Values can be passed directly

System Verilog Concepts DPI(Direct Programming interface )  Imported functions  Exported functions • System verilog calls the C functions • C calls the system verilog function  Both sides of DPI are fully independent • System verilog does not analyze the C-code • C complier does not have to analyze the system verilog code

System Verilog Concepts Top SystemVerilog Testbench Constructs  Queue  Mailbox  Fork/join  Class  Constraint  Covergroup  Program  Virtual interface  Clocking Block  modports

Verification Targeted Capabilities

DUT Driver Transactor Monitor Supplies data to the DUT Observes data from DUT Executes transactions Identifies transactions Checks correctness Creates stimulus Testbench Assertions Test Checker Self Check Verification Environment Verification environment

Verification targeted capabilities  File I/o  Random number generation  Fork/join  Initial block  Task & functions  PLI All verilog features  Constrained random number generation  Classes  Fork/join_any,fork/join_none  Final block  Task & function enhancements  DPI Verilog System Verilog

What is OOP? OOP encapsulation classes polymorphism inheritance

 OOP is object oriented programming  Classes form the base of OOP programming  Encapsulation - OOP binds data & function together  Inheritance –extend the functionality of existing objects  Polymorphism – wait until runtime to bind data with functions What is OOP?

What is OOP?  OOP breaks a testbench into blocks that work together to accomplish the verification goal  Why OOP • Highly abstract system level modelling • Classes are intended for verification • Classes are easily reused and extended • Data security • Classes are dynamic in nature • Easy debugging, one class at a time

Why system Verilog? Why Not C++? Why not C++

C++ System Verilog  Superset of Verilog  RTL/Verification language  Assertion language  Constraint language  Code coverage language  No relation to verilog  Interface is required to interact with Verilog Why not C++

Inheritance  Inheritance is to reuse the existing code  Inheritance allows to add new • Data members(properties) • New Methods  Inheritance is to share code between classes

Inheritance Advantages • Common code can be grouped into one class • No need to modify the existing classes • Add new features to existing class by means of new derived classes • Easy debug & easy to maintain the code base

Randomization Why Randomization ? • Random generation of stimulus • Random setting of parameters • Hard-to-reach corner cases can be reached

Shift from directed to random Randomization Directed Random  Detect the expected bugs  Time consuming  Detects unexpected bugs (corner cases)  Tremendously reduce the efforts

Randomization  Constrained Randomization  Improves the result  Speed-up the bug finding process  More interesting cases can be achieved within the constrained boundary

Assertion  Used primarily to validate the behaviour of a design  An assertion is a statement about a designs intended behaviour  In-line assertions are best added by design engineers  Interface assertions are best added by verification engineers  An assertion’s sole purpose is to ensure consistency between the designer’s intention and design implementation  It increases the bug detection possibility during RTL design phase

Crux SystemVerilog  Is a unified language (HDVL)  Reduce the design cycle  Verify that designs are functionally correct  Greatly increase the ability to model huge designs  Incorporates the capability of Vera & powerful assertion constructs  Bridges the gap between Hardware design engineer and verification engineer

Verification with SystemVerilog

This Presentation is…  Focused on “SystemVerilog” Testbench constructs  It’s a platform for open discussion on “SystemVerilog”

References Websources: 1. www.systemverilog.org 3. http://svug.org/ Books : 1. Writing Testbenches using SystemVerilog - Janick Bergeron 2. Verification Methodology Manual - Janick Bergeron 3. SystemVerilog For Verification - Chris Spear

Top SystemVerilog Testbench Constructs  Queue  Mailbox  Fork/join  Semaphore  Constraint  Covergroup  Program  Interface  Clocking Block  modports We will discuss…

Queue…  Data storage array [$] • Variable size array with automatic sizing • Searching, sorting and insertion methods

Mailbox  Fifo with flow control • passes data between two processes • put() – stimgen calls put() to pass data to bfm • get() – bfm calls get() to retrieve data from stimgen mailbox stimgen bfm put() get()

Mailbox mailbox mbx; mbx = new(); // allocate mailbox mbx.put(data); // Put data object into mailbox mbx.get(data); // data will be updated with data from FIFO success = mbx.try_get(ref data); // Non-blocking version mbx.peek(data); // Look but don’t remove count = mbx.num(); // Number of elements in mailbox

Fork/join join fork Fork/join Initial Begin Clk =0; #5 Fork #5 a = 0; #10 b = 0; Join Clk= 1; end Clk becomes 1 at t=15

Fork/join Join_any fork Fork/join_any Clk becomes 1 at t=10 Initial Begin Clk =0; #5 Fork #5 a = 0; #10 b = 0; Join_any Clk= 1; end

Fork/join Join_none fork Fork/join_none Clk becomes 1 at t=5 Initial Begin Clk =0; #5 Fork #5 a = 0; #10 b = 0; Join_none Clk= 1; end

Semaphore  Used for Synchronization • Variable number of keys can be put and removed • controlled access to a shared object • think of two people wanting to drive the same car – the key is a semaphore

Constraint  Control randomization • Values for random variable can be controlled through constraint expressions • These are declared within constraint block Class packet ; rand logic [7:0] src; rand logic [7:0] dest; Constraint my_constraints { src[1:0] == 2’b00; // constraint expression …………… // always set src[1:0] to 0 } endclass:packet

Covergroup  Captures results from a random simulation  Encapsulates the coverage specification • bins • transitions Covergroup check @(posedge top.valid ); coverpoint global; coverpoint top.test; endgroup:check ……………… check chk = new();

Program Block  Benefits: • Encapsulates the testbench • Separates the testbench from the DUT • Provides an entry point for execution • Creates a scope to encapsulate program-wide data  Functionality: • Can be instantiated in any hierarchical location Typically at the top level • Ports can be connected in the same manner as any other module • Executes in the SV reactive region

Program Block The testbench (program) runs separately from design (module) • Triggered by clock • Samples just before clock edge, drives just after clock clock Sample inputs Drive outputs Design Testbench

Interface  bundling of port signals • provide an abstract encapsulation of communication between blocks • Directional information (modports) • Timing (clocking blocks) • Functionality (routines,assertions) device1 device2 interface

Interface Interface bus_a (input clock); logic [7:0] address; logic [31:0] data ; bit valid ; bit rd_wr ; Endinterface: bus_a Interface:An example

Clocking Block  Specify synchronization characteristics of the design  Offer a clean way to drive and sample signals  Features • Clock specification • Input skew,output skew • Cycle delay (##)

Clocking Block  Can be declared inside interface,module or program

Clocking Block Module M1(ck, enin, din, enout, dout); input ck,enin; input [31:0] din ; output enout ; output [31:0] dout ; clocking sd @(posedge ck); input #2ns ein,din ; output #3ns enout, dout; endclocking:sd reg [7:0] sab ; initial begin sab = sd.din[7:0]; end endmodule:M1 Signals will be sampled 2ns before posedge ck Signals will be driven 3ns after posedge ck

Modports  An interface can have multiple viewpoints • Master/Slave, Transmitter/Receiver  These can be specified using modports Interface bus_b (input clock); logic [7:0] addr,data; logic [1:0] mode ; bit ready ; modport master (input ready,output addr,data,mode) ; modport slave (input addr,data,mode,output ready) ; endinterface: bus_b All signal names in a modport must be declared in the interface

Conclusion  Some of SystemVerilog Testbench constructs were discussed  But still a long way to go……..

SystemVerilog_veriflcation system verilog concepts for digital vlsi.ppt

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