Advanced Debug With Questa

Chuck Seeley

Verification Technologist

DVT

� Introduction

� Debug Enhancements for Traditional Languages

� Debugging Constraints

� Debugging Assertions

� Debugging Dynamic Objects

Agenda

� Designs grow ~2x every 18 months

— Moore’s law still applies

� Verification requirements grow faster

— 2x more logic and complexity to verify

— Higher quality verification demanded

Today’s Verification

� Companies with the highest verification productivity

— Get new products to market faster

— Take maximum advantage of Moore’s law

— Build the most competitive products

Debug - A Big Challenge

� Designs continue to include Verilog/VHDL/SystemC

and now SystemVerilog

� Transition to HVL improve verification productivity

at the price of debug productivity

— Introduces new debug paradigm

� OVM delivering advanced techniques to everyone

� Ability to create unknown “out-of-body” code

experiences

Language and methodology are the starting point

Questa - Advancing Productivity

Class browsing & wave viewingSV/SystemC thread debugging

UPF Power-Aware SystemC TLM 2.0

Time to next simulation improvements

6.4

June 08

Verification Management

SV OVM 1.0Power-Aware Simulation

SV&SC Transaction ViewAssertion Thread View

Post-Sim Debug

6.3

May 07

SV Testbench/AVM 2.x Unified Coverage Database

VOPT SV, VHDL & SystemCFull SystemC TLM

FSM extractionSource Code Annotation

6.2

April 06

6.1

SV Testbench/AVM 1.xSVA and PSL

Functional coverageVOPT Verilog

TLM support

June 05

6.0

SystemCSystemVerilog

VHDL and VerilogModernized GUI

Aug 04

Window ManagerHyperlinked navigation

FSM ViewingVHDL Hierarchical

ReferencesVHDL Encryption

Lossless Cover Merge

6.5

Q1 09

� Leader in mixed language interoperability

� Highest performance for gate-level, RTL and TLM

� Fastest, highest capacity Unified Coverage Data Base (UCDB)

� Powerful Verification Management tools to reach coverage closure faster

� Unified debug for all languages and abstraction levels

Proven Technology

Questa – The Most Advanced Functional Verification Platform

� Introduction

� Debugging Enhancements for Traditional Languages

� Debugging Constraints

� Debugging Assertions

� Debugging Dynamic Objects

Agenda

Easing Processes Debug

View all processes

together regardless of

language

Toggle between

viewing modes

All Windows linked to process window

Integral with SystemC Debug

Interface

Message Viewer

Source Code Annotation

� Linked to cursor location in wave window

� Linked to dataflow window

Textual Dataflow: Tracing Signals

Find reader of strb_r

Select Signal then RMB

Textual Dataflow: Tracing Signals

Find driver(s) of prdy_r

Select Signal then RMB

Drop Source To Waveform

Wave Window: Signal Grouping

Group signals

under user

defined name

Drag & drop

signals into and

out of group

Drag & drop

group as one

object

Collapse &

expand group

as needed

Wave Window: Expanded Time

� Expand the Wave Window to view all transitions

during a single time step.

Indicates multiple transitions

Blue background indicates

expanded section

Delta-time steps

16

Easing Causality TracingSource Code Hyperlinking

Optional source code hyperlinking

Hyperlinked variables

17

Jump to source window and Jump to source window and

highlight variable declarationhighlight variable declaration

Easing Causality TracingSource Code Hyperlinking

Comprehensive FSM Debug Solution

State diagram animation linked

to active wave cursor

State variables identified

with FSM icon

Select FSM from list

FSM Debug with transition expressions

Control display of:* Transition counts

* State counts* Conditional paths

* Balloon popups* Wave cursor linking

FSM states:* Brown - Reset state

* Yellow - Previous state* Green - Present state

* Blue - Not one of the above

� Introduction

� Debugging Enhancements for Traditional Languages

� Debugging Constraints

� Debugging Assertions

� Debugging Dynamic Objects

Agenda

Failures during Randomization

Error reported for

failed randomization of a class object

Debugging Constraint Solver

� On randomize() failure, display the minimum set of

constraints that caused failure

— Default is off

— Setting SolveFailDebug in the modelsim.ini file

SolveFailDebug = 1

— Using -solvefaildebug on vsim command line

vsim –solvefaildebug

— Using verilog attribute in source code

randomize (* solvefaildebug=1 *) (a, b) with {a > b; a < b;};

Debugging Failures in Constraint Solver

� Derived class constraint

contains a conflict

— c0 in child

— c1 and c2 in parent

� vsim –solvefaildebug …

� Simulator output:

class TFoo;

rand bit [5:0] a, b, c;

constraint c1 { a < b; }

constraint c2 { b < c; }

constraint c3 { a < 23; }

constraint c4 { b > 12; }

constraint c5 { c == 20; }

endclass

class TBar extends TFoo;

constraint c0 { a == c; }

endclass

TBar f = new;

int status;

$display("status = f.randomize();");

# test.v(22): randomize() failed due to conflicts between the following constraints:

# test.v(5): ((f.a)<(f.b))

# test.v(6): ((f.b)<(f.c))# test.v(13): ((f.a)==(f.c))

Constraint Solver Performance

� Adjusting performance for certain types of constraints

— May improve or decrease performance

— Command line: -solveflags=<flags>

— modelsim.ini file: SolveFlags = <flags>

� Valid flags are:

i = disable bit interleaving for >, >=, <, <= constraints

n = disable bit interleaving for all constraints

r = reverse bit interleaving

� Getting more information about what solver is doing

— Command line: –solveverbose [1 or 2]

— Verbose messaging typically requires interpretation by R&D

� Introduction

� Debugging Enhancements for Traditional Languages

� Debugging Constraints

� Debugging Assertions

� Debugging Dynamic Objects

Agenda

Simulation With Assertion

� Questa ABV added value

—Advance Debug capabilities for PSL & SVA

� Integrated Assertion Browser

�View assertions in wave window

�Assertion Thread Viewer

—Best root cause analysis

Analysis Window

Capacity Details Analysis WindowPinpoint effects of Assertions on

Performance & Memory Usage

Effects of Cover Directives

Effects of

Covergroups

Viewing Assertions in the Wave

Green mid-line

indicates assertion is active

Blue low-line

indicates assertion is

inactive

Simply D&D Assertions from Assertion Browser into Wave Window to view assertions

Assertions can be expanded to view all signals associated with the assertion

Red inverted triangle

indicates assertion

failure

Green triangleindicates assertion

passed

Multiple Threads in Wave Window

Automatic Thread count

integer

Expand to see

individual thread

RMC on start of thread box

invokes ATV

Blue box above thread

indicates start of new

thread

Advanced Assertion Debug with ATVExpanded assertion

Yellow dot indicates additional thread spawned

Green dot indicates

expression is true

Redundant failure:

individual spawned thread failed but other threads still active

Red dot indicates

expression is false

Local variable

pane

ATV and Local Variables

Toggle Local Variable Pane

Annotation of local

variable on selected thread

Blue boxes indicate local variable sampling

Wave Window: Signal Grouping

Group signals

under user

defined name

Drag & drop

signals into and

out of group

Drag & drop

group as one

object

Collapse &

expand group

as needed

� Introduction

� Debugging Enhancements for Traditional Languages

� Debugging Constraints

� Debugging Assertions

� Debugging Dynamic Objects

Agenda

Viewing/Debugging SV Class Objects

� Information about SV class objects available in

several forms:

— Objects/Locals Windows

— Watch Window

— Class Tree/Class Graph

— Structure Window

� SV testbench structure for AVM/OVM

— Wave Window

� Transaction Viewing and Classes objects

Debugging Dynamic Objects

� View class contents and property values

— Useful when setting breakpoints & single stepping

Enhanced Watch Window

Understand class relationshipsSee class member values

Highlight selected relationship

� Display values for signals & variables

— View dynamic and static objects together

� arrange objects independently

� object grouping

� quickly scroll window with mouse panning

Class Tree Window

Classes can beorganized by

extended class

View all methods &

properties within a class

Classes can also beorganized by base

classView parent/child

relationship

Class Graph Window

Graph window shows all methods & properties

Zoom out to see entire hierarchy

Hover cursor over block to see name

Default view organized by extended class, can also

be viewed by base class

Transaction Viewing: The Wave Window

� OVM/AVM stimulus are transactions in streams of data

� Questa SV Transaction API enables viewing of any SV

transactions View and debug at the transaction level

OVM/AVM Classes and Questa

� Questa extracts SV TB structure from OVM/AVM class based environment

— OVM/AVM source code instrumented with Questa specific PLI calls� TB extraction occurs automatically only when using pre-compiled OVM/AVM

package or source code (Closed kit)

— OVM/AVM “static” component classes are converted into design scopes� Includes ovm_components, analysis/tlm_fifos’s, ovm_subscriber

� Object window contents are filtered to show only user added members

� Visible in sim tab of Workspace after run 0 (after OVM’s end_of_elab phase)

OVM ENVOVM ENV

DUTDUT

Workspace Instances

module cpu_wb_environment;

cpu_wb_agent wb_agent();

eth_mii_rx_agent rx_agent();

eth_mii_tx_agent tx_agent();

endmodule

� Module based hierarchy created by vopt/vsim

elaboration

class cpu_wb_environment extends ovm_env;

cpu_wb_agent wb_agent;

eth_mii_rx_agent rx_agent;

eth_mii_tx_agent tx_agent;

function new(…) … endfunction

function void build;

wb_agent = new("wb_agent",this);

rx_agent = new("rx_agent",this);

tx_agent = new("tx_agent",this);

endfunction // new

endclass

module top;

cpu_wb_environment env;

initial begin

env = new(“env”);

env.run_test();

end

endmodule

Workspace Instances

� Component hierarchy created at runtime

Other Windows and OVM TB Class scenario_base is not an ovm_component

scenario_base class reference can be added to and viewed

in the wave window

Wave window

name reflects static class hierarchy

@333 is the value assigned

to scenario_bases’class variable

Environment Class

converted to a scope

Object Window contents are

filtered to show only user added members

Sub-Env components converted to scopes

Class Objects in Wave Window

Class variable value assigned by simulator

View a class object by adding specific class

variable to wave window

Summary

� Questa’s debug features which will increase your verification productivity

— industry leading integrated and interactive debugging features supporting mixed languages in single environment

� Questa’s debug features will increase verification productivity of traditional languages and techniques

— Verilog, VHDL, and SystemC

� Questa’s supports advanced debug features required by today’s advanced verification languages and methodologies

— SV based verification methodologies� OVM/AVM/VMM

— Dynamic object support� SV/SC Transaction and Class viewing

— Assertion Based Verification� SVA and PSL