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SoC Verification Strategies for Embedded Systems Design

November 5-6, 2003/ Seoul

Chong-Min Kyung,KAIST

SOC Design Conference

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Various Embedded Mobile Systems

Desktop PC

Data Processing Consumer

Communication Automotive & etc.

DTV

MediaCenter

GameConsole

DSC

DVC

Car Navigation

DVD

Telematics

MP3 Player

Credit CardCellular Phone

Notebook PC

Internet

Smart Phone PDA

Bluetooth

Audio

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Difficulties in Embedded Systems Design

(What’s special in ES design?) Real operating environment of ES is

difficult to reproduce. -> In-system verification is necessary.

Total design flow of ES until the implementation is long and complex. -> Verification must be started early.

Design turn-around time must be short as the life-time of ES itself is quite short. -> Short verification cycle

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Three Most Important Issues in Verification

1. Verify Right : Always make sure you have correct specifications to

start with. (Frequent interaction with SPECIFIER, customer, marketing, etc.)

In-System Verification Check Properties in Formal Techniques.

2. Verify Early System-level, Heterogeneous Models, SW-HW

3. Verify Appropriately HW-SW Co-simulation

4. Verify Fast Hardware Acceleration, Emulation

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Strongly Required Features of Verification

Accommodate Multiple Levels of Design Representation

Exploit Hardware, Software and Interfacing mechanisms as Verification Tools

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Virtual Chip : “Verify Early, In-System”

Virtual Chip: Making Functional Models Work on Real Target System [DAC98]

Simulating ISS of a Processor Chip along with real target environment

Target board

Host computeras Virtual Chip cable

Pin Signal Generator with Buffers

Chip Model;ISS

Chip Socket

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PC running ISS

Without CPU

Picture taken in 1993 or 1994

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Reducing TTM using Virtual Chip

idle

Conventional design flowConventional design flowArchitectural

modelRTL

modelGate-level

modelH/W

Emulation

Verification w/ H/W

H/W prototype(H/W emulation)

Boarddesign

H/W System

ApplicationS/W

idle

design

Virtual Chip design flow; EARLY ,IN-SYSTEMVirtual Chip design flow; EARLY ,IN-SYSTEMArchitectural

model

H/W prototype(Virtual ChipVirtual Chip)

Boarddesign

H/W System

design

RTLmodel

Gate-levelmodel

H/WEmulation

Verification w/ H/W

ApplicationS/W

Design time is drastically reduced

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Microprocessor Design Verification Methodology

InstructionBehavior

In C(Polaris)

Micro-architecture

in C

RTLVerilog

Gate-LevelVerilog

RealMother-board

H/WVirtual PC in C (VPC)

C Language

Target Environment

HDL

MCV : Microcode VerifierMCV : Microcode Verifier PLI : Programming Language InterfacePLI : Programming Language Interface

more refined model

MCVFlexPCVirtual Chip PLI

CPU Model

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HK386 (1995)

Design Specification Instruction level, Pin-to-Pin compatible

with i386 Operation speed : 40 MHz 0.8 m DLM CMOS ASIC

Test Programs MS DOS 6.0, Windows 3.1, Office 4.0 CAD tools, games, etc..

MS Win. 3.1 MS Office MaxPlus II

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What about Emulation? Swallowed a lot of Money Required a separate, air-conditioned room Needed a lot of time for Compile Needed an expensive slowed-down PC ($20,000

for 500kHz clocking)

However…worked at the last minute Finding bugs is not easy

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x86 Emulation Configuration

HardwareEmulator

500kHz Slowed-Down PCProbeModule

Target InterfaceBoard

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Booting Windows 20M instructions on Marcia

02000400060008000

100001200014000160001800020000

0 5 10 15 20 25 31 36 41Time (weeks)

Inst

ruct

ions

(tho

usan

d)

HDL saverAttached

Windows

DOS

HDL Simulation HardwareEmulation

setupversionupdate 1

versionupdate 2

versionupdate 3

Simulation debugs,Emulation approves.

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Agenda Verify Early and Altogether (In-System) Why Verification ? Verification Alternatives Verification with Progressive Refinement SoC Verification Concluding Remarks

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Trend of Verification Effort in the Design

Verification portion of design increases to anywhere from 50 to 80% of total development effort for the design.

Code Verify (30 ~ 40%)Synthesis P&R

Code Verify (50 ~ 80%) Synthesis P&R

1996300K gates

20001M SoC

Verification methodology manual, 2000-TransEDA

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Percentage of Total Flaws About 50% of flaws are functional flaws.

Need verification method to fix logical & functional flaws

From Mentor presentation material, 2003

Clocking5%

Race5%

Power4%

Other9%

Yield7%

Noise12% Slow Path

13%

Logical/Functional

45%

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Another recent independent study showed that more than half of all chips require one or more re-spins, and that functional errors were found in 74% of these re-spins.

With increasing chip complexity, this situation could worsen.

Who can afford that with >= 1M Dollar NRE cost?

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Bug Fixing Cost in Time Cost of fixing a bug/problem increases as design

progresses. Need verification method at early design stage

Verification methodology manual, 2000 – TransEDA

Behavioral

Design

RTLDesign

Gate Level

Design

DeviceProductio

n

Cost ofFixing

a Problem

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Verification Performance Gap; more serious than the design productivity

gap Growing gap between the demand for verification

and the simulation technology offered by the various options.

System-on-a-chip verification, 2001 – P.Rashinkar

Event-base simulation (<10CPS)

Cycle-base simulation (<1KCPS)

HW simulation acceleration (<10KCPS)

Design complexity

Sim

ulat

ion

perf

orm

ance

Veri

ficat

ion

com

plex

ity

Verification Performance Gap

SmallSmallASICASIC

MediumMediumASICASIC

ComplexComplexASICASIC

SOCSOC

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Completion Metrics; How do we know when the verification is done?

Emotionally, or Intuitively; Out of money? Exhausted? Competition’s product is there. Software people are happy with your hardware. There have been no bugs reported for two weeks.

More rigorous criteria; All tests passed Test Plan Coverage Functional Coverage Code Coverage Bug Rates have flattened toward bottom.

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Verification Challenges Specification and/or Operating Environment is Incomplet

e/Undetermined. (Just like last-minute ECO!) Cannot avoid using Yesterday’s tool for Today’s Design. Design productivity grows faster than Verification producti

vity. (Verification productivity Gap) Besides Functional Verification, Estimation on Performan

ce, Power Consumption becomes crucial issues in SoC design.

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Agenda Verify early and in-system Why Verification ? Verification Alternatives

Simulation Hardware-accelerated simulation Emulation Prototyping Formal verification Semi-Formal (Dynamic Formal) verification

Verification with Progressive Refinement SoC Verification Concluding Remarks

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Overview of Verification Methodologies

Simulation

HardwareAcceleratedSimulation

Emulation

FormalVerification

Semi-formalVerification

Prototyping

Faster speed, closer to final product

Bigger coverage

Basicverificationtool

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Software Simulation Pros

The design size is limited only by the computing resource.

Simulation can be started as soon as the RTL description is finished.

Set-up cost is minimal. Cons

Slow (~100 cycles/sec) ; Speed gap between the speed of software simulation and real silicon widens. (Simulation speed = size of the circuit simulated / speed of the simulation engine)

The designer does not exactly know how much percentage of the design have been tested.

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Hardware-Accelerated Simulation Simulation performance is improved by moving

the time-consuming part of the design to hardware.

Usually, the software simulation communicates with FPGA-based hardware accelerator.

Simulation environment

Testbench

Module 0

Module 1

Module 2

Hardware Accelerator

Module 2 is synthesized &compiled into

FPGAs

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Hardware-Accelerated Simulation Pros

Fast (100K cycles/sec) Cheaper than hardware emulation Debugging is easier as the circuit structure is unchanged. Not an Overhead : Deployed as a step stone in the

gradual refinement Cons (Obstacles to overcome)

Set-up time overhead to map RTL design into the hardware can be substantial.

SW-HW communication speed can degrade the performance.

Debugging of signals within the hardware can be difficult.

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Emulation Imitating the function of another system to

achieve the same results as the imitated system. Usually, the emulation hardware comprises an

array of FPGA’s (or special-type processors) and interconnection scheme among them.

About 1000 times faster than simulation.

Simulation

HardwareAcceleratedSimulation

Emulation

Prototyping

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Emulation Pros

Fast (500K cycles/sec) Verification on real target system.

Cons Setup time overhead to map RTL design into

hardware is very high. Many FPGA’s + resources for debugging

high cost Circuit partitioning algorithm and

interconnection architecture limit the usable gate count.

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Emulation Challenges

Efficient interconnection architecture and Hardware Mapping efficiency for Speed and Cost

RTL debugging facility with reasonable amount of resource

Efficient partitioning algorithm for any given interconnection architecture

Reducing development time (to take advantage of more recent FPGA’s)

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Prototyping Special (more dedicated and customized)

hardware architecture made to fit a specific application.

Simulation

HardwareAcceleratedSimulation

Emulation

Prototyping

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Prototyping Pros

10X higher clocking than emulation Components as well as the wiring can be

customized. Can be carried and dispatched for demo or

customer evaluation Cons

Not flexible for design change (Even a small change requires a new PCB.)

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Overview of Verification Methodologies

Formal verification Application of logical reasoning to the development of

digital system Both design and its specification are described by a

language in which semantics are based on mathematical rigor.

Semi-formal verification Combination of simulation and formal verification. Formal verification cannot fully cover large designs,

and simulation can come to aid in verifying the large design.

Simulation FormalVerification

Semi-formalVerification

More complete verification

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Formal Verification Classes

Model Checking : verifies that the design satisfies properties specified using temporal logic

Equivalence Checking Symbolic Simulation Theorem Proving

Pros Assures 100% coverage. Run fast.

Cons Works only for small-size finite state systems due to

memory explosion. (so far, <500 flip-flops) Uncomfortable, i.e., need to learn temporal logic for

“property” description in Model Checking

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Efforts by Formal People to reduce the Complexity

Reachability analysis Design state abstraction Design decomposition

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Semi-Formal Verification - Assertion

Assertion-based verification (ABV) “Assertion” is a statement on the intended

behavior of a design. The purpose of assertion is to ensure

consistency between the designer’s intention and the implementation.

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Semi-Formal Verification - Assertion

Simulation Quality of assertion-based verificationN

umbe

r of b

ugs

foun

d

Time, EffortSetup testbench

Describe assertions

Formal verificationSimulation

Simulation with assertionsEfficiency of assertion

By IBM in “Computer-Aided Verification” 2000

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Semi-Formal Verification - Coverage

Coverage-directed verification Increase the probability of bug detection by checking

the ‘quality’ of stimulus Used as a guide for the generation of input stimulus

Test Plan(Coverage Definition)

DirectivesRandom

Test Generator

Test Vectors

SimulationCoverage analysis

Coverage Reports

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Semi-Formal Verification Pros

Designer can measure the coverage of the test environment as the formal properties are checked during simulation.

Cons Simulation speed is degraded as the properties are

checked during simulation. Challenges

Guiding the direction of test vectors to increase the coverage of the design.

Development of more efficient coverage metric to represent the behavior of the design.

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Speed Comparison

0 kHzSoftwareSimulation

10 kHz

1MHz

Hardware-AcceleratedSimulation (from Quickturn/Dynalith Presentation)

Hardware emulation

(from Quickturn presentation)

100kHz

500KHz

100Hz

100 kHz

Speed (Cycles/sec, log scale)

10MHz 1~10MHz

Prototyping Semi-formal(Assertion-

based verification)

50-70Hz

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Verification Time vs. Coverage (not to exact scale): Which best fits your

application?Coverage

Verification Time

Simulation

Semi-formalPrototyping

Emulation/Simulation Acceleration

Simulation setup

Semi-formal setup

Emulation/SA setup

Prototyping setup

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Agenda Verify early and in-system Why Verification ? Verification Alternatives Verification with Progressive Refinement

Flexible SoC verification environment Debugging features Cycle vs. transaction mode verification

SoC Verification Concluding Remarks

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Criteria for Good SoC Verification Environment

Support various abstraction levels Support heterogeneous design languages Trade-off between verification speed and

debugging features Co-work with existing tools Progressive refinement Platform-based design

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Core model

ISS

Transaction-Level Modeling Model the bus system in transaction-level

No notion of exact time. But precedence relation of each functional block is

properly modeled. Rough estimation on performance is possible. Used as the fastest reference model by each block

designer

Memory IP IP

Transaction-level Bus model

RoughPerformanceEstimation

...

...

Behaviormodel

------

------

------

Software design Hardware design

transaction

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Core model

ISS

Cycle-Accurate Bus Modeling For more accurate modeling

Build a cycle-accurate system model in C or SystemC Replace the transaction-level bus model with a cycle-accurate b

us model ARM released a “Cycle-Level Interface Specification” for t

his abstraction level.

Memory

IP

IP

Cycle-accurate Bus model

AccuratePerformanceEstimation

...

...

Behaviormodel

------

------

------

transaction

BFM BFM BFM

RTLmodel

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AMBA AHB CLI Specification AMBA AHB Cycle Level Interface (CLI) Specification

CLI spec defines guidelines for TLM of AHB with SystemC. Interface methods Data structures Header files for SystemC models

CLI spec leaves the detailed implementation of the AHB bus model to the reader.

master

slave

masterHADDRHWRITE

HRDATAHTRANS

slave

Read 10 data from slaveX startingAddress 0x10

Cycle-level modeling Transaction-level modeling

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AMBA AHB CLI Specification Example master implementation

Transactions are represented as methods in transaction-level modeling.

Abstraction levels of each method can be decided as needed such as cycle-count accurate, cycle-accurate, transaction accurate, etc.

void masterA::run(){ bus_request(); has_grant(); init_transaction(); read_from_slave(); ...}

Header Body

The granularity of transactions are decided according to the verification needs.

SC_MODULE(masterA) { ... ... void run();};

masterA.h masterA.cpp

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Flexible SoC Verification Environment

Build C reference model for the target application.

Setup of platform-level verification environment as early as possible

JPEG decoding

HEAD VLD IDCT DISP

Verification Environment Setup

Functional block model

TRS TRS TRS TRS

HEAD VLD IDCT DISP

Platform-level model

Algorithm

Memory Timer INTC

SW Model

HW Model

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Flexible SoC Verification Environment

Transactor connects various types of SW block models with HW bus system.

Several types of transactors must be prepared, for example AHB C model AHB HDL model OPB Testbuilder PLB SystemC

JPEG decoding

HEAD VLD IDCT DISP

Verification Environment Setup

Functional block model

TRS TRS TRS TRS

HEAD VLD IDCT DISP

Platform-level model

Algorithm

Memory Timer INTC

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Flexible SoC Verification Environment

Socketize IP representation HW: C HDL EDIF SW: native C ISS Processor Core

C

Transactor

HDL

AHB

C to HDL

EDIF

Synthesis

Transactor

C

AHB

ISS

AHB

Processor

Cross-compiler

Transactor

Transactor

Transactor

SW partmodel

HW partmodel

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Cycle-Level Transactor Generate stimulus at every clock cycle Check the result of DUT at every clock cycle

PCIController DUTPCI

ChannelTestbench

Testbench DUT

FPGA part

DeviceDriver

S/W simulation part

Cycle-leveltransactor

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Transaction-Level Transactor Only information to generate transaction is

transferred to DUT, i.e., address and data No need to synchronize at every clock cycle

PCIController DUTDMA

ChannelTestbench

Testbench DUT

FPGA part

DeviceDriver

S/W simulation part

Transactor

MainMemory

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Cycle vs. Transaction-level Transactor

Cycle-level transactor Synchronized at every clock cycle. Operating speed depends on the number of signals to be transf

erred. Transaction-level transactor

Synchronized at the end of each transaction. Transactor must be designed for each interface standard

ex) AHB transactor, SDRAM transactor, IIS transactor

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DFV (Design for verification) : OpenVera (OV) verification IP

Reusable verification modules, i.e., 1) bus functional models, 2) traffic generators, 3) protocol monitors, and 4) functional coverage blocks.

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RTL Debugging Feature Gate-level netlist generated from the synthesis tools is di

fficult to trace manually. Techniques to resolve RTL symbol names from the gate-l

evel symbol names and to provide debugging environment in RTL name spaces is required.

Insert RTL instrumentation IP for debugging Design flow

Read RTL design (Verilog, VHDL) Generate instrumented RTL design (spiced with triggering and dump

logic) Synthesis Compile (mapping & PAR)

DiaLite (Temento), Identify (Synplicity)

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Synthesizable Testbench Prepare a set of programmable test bench

module which can be also synthesized into hardware.

To verify a DUT, build a test bench using the programmable test bench.

The test bench is applicable to both simulation and emulation in the same fashion.

from Duolog TechnologGeneric Mini-Controller(GMC)

gmc_cfg_datasize 3 # Set to 32 Bitsgmc_cfg_msmode 0xF # Set to Master TXgmc_cfg_datapath_0x00 # Read/Write to Memgmc_cmd_send_data 100 # Send 100 Bytesuart_cfg_odd_parity 1 # Set ODD parity

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Agenda Verify early and in-system Why Verification ? Verification Alternatives Verification with Progressive Refinement SoC Verification

Co-simulation Co-emulation

Concluding Remarks

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SoC Verification Co-simulation

Connecting ISS with HDL simulation environment Seamless, N2C

Co-emulation Emulation/rapid-prototyping equipments supporting co

-emulation ARM Integrator, Aptix System Explorer, AXIS XoC, and Dynalith iPROVE

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What’s the point in SoC Verification? Mixture of SW and HW

Let the HW model to cooperate with Processor Model such as ISS or BFM (Bus functional model)

Mixture of pre-verified, unverified components Utilize legacy IPs already verified

Mixture of different language, different abstraction levels Provide common interface structure between SoC components

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Canonical SoC design flow

SystemSpec.

SystemDesign

HW/SWPartitioning

HWDevelopment

SWDevelopment

HW refinement(UT->T->RTL)

Gate

HW IP

SW IP

SoftwareVerification

FunctionalVerification

Gate-LevelVerification

HW-SWCo-Design

HW-SWCo-

Verification

SW refinement(RTOS

mapping)

Final code Emulator

In-system emulator HW-SW co-debugging

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Tools for HW-SW Co-Verification

HW-SW co-simulation ISS RTOS simulator

HW/SWPartitioning

HWDevelopment

SWDevelopment

HW refinement(UT->T->RTL)

SoftwareVerification

FunctionalVerification

Co-Verification

SW refinement(RTOS

mapping)

HW-SW

High-level synthesis Testbench automation IP accelerator

SystemSpec.

SystemDesign

HW/SW

HW IP

SW IP

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Tools for System-level Verification

System-level design (Performance analysis tools) Hot-spot analyzer High-level cycle count estimation High-level power analysis High-level chip area estimation On-chip-bus traffic estimation

SystemSpec.

SystemDesign

HW/SWPartitioning

HW IP

SW IPHW-SW

Co-Design

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Co-Simulation Tools Software debugging in ISS and hardware

verification in HDL simulator are done in parallel way.

Co-simulation stub manages the communication between HDL simulator and ISS.

The most accurate solution albeit very slow

ISS HDLSimulator

Co-simulationStubDebugger

RemoteDebuggingInterface

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Co-Emulation Tools Link hardware emulators with a processor model

running in host machine or an actual processor core module

Most emulation and rapid prototyping products support linkage with ISS running in host machine

As the emulator runs very fast, speed of ISS including memory access as well as synchronization between emulation and ISS rise as new bottlenecks in verification

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Example) ARM ETM (Embedded Trace Macrocell)

Real-time trace module capable of instruction and data tracing dedicated to the ARM core family

Triggering enables to focuscollection around the region of interest

Trace module controls theamount of trace data by filtering instructions or data

Only applicable to the ARMcore debugging

ARMARMcorecore

Memories Peripherals

Othe

r com

pone

nts

ETM

Target system with ARM based ASIC

PC-based debugger

TraceTrigger

Traceport

analyzerJTAG

interface

Conf.

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Typical Co-Emulation Environment Connect ARM ISS or ARM board to the emulation

system.

ARM ISS EmulationSystem

ARMDevelopment

BoardEmulation

System

ARM ISS can be configured to user’s target SoC architecture.

SW debugger can be fully utilized.

Faster than ISS. Ready-made ARM development

boards has fixed architecture which may be different from the user architecture.

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Example 1: ARM Integrator ARM prototyping platform Composed of

Platform : AMBA backbone + system infrastructure Core Module : various ARM core modules (up to four) Logic Module : FPGA boards for AMBA IP’s

Allows fast prototypingof ARM-based SoC

Enables co-emulationof both software in ARM processor core andhardware in the FPGA

Difficult to debug hardwarelogic

from ARM

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FPGA

Hardware Sessions

C/SystemC/HDL sessions

HardwareProcessor

Logic Designin EDIF/FPGA

Transactor Transactor

Target board

I/F protocol I/F protocol

Inter-Lingual Communication

Designin C

Example 2 : iSAVE/iPROVE (Dynalith) All-in-one verification :

Heterogeneous models including ARM ISS, C hardware model, HDL hardware description

SW models run in Linux-based PC HW models run in FPGA’s, or as a processor chip

HW/SW Co-debugging with Pin Signal Analyzer

On-the-fly probing of FPGA internal signals to SRAM

Communicate with C modelusing PCI DMA

ISS sessions

ISSDesignin SC

Designin HDL

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Agenda Verify early and in-system Why Verification ? Verification Alternatives Verification with Progressive Refinement SoC Verification Concluding Remarks

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So, in Summary… Verification is challenging; It needs strategy! Strategy is to apply each method when appropriate. Verify with Correct Specification

In-System Verification Verify as early as possible; Kill the bug when it is small a

nd still isolated in a smaller region. (Kill it before it grows big and kills you(r design and your company).)

Accelerate the verification cycle using Efficient debugging tools Hardware Accelerator

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A Tactical Sequence of Applying Various Verification Tools

1st step: Apply formal methods Static formal verification Assertion-based verification

2nd step: Simulate IP with transaction level test-bench with cycle-accurate test-bench

3rd step: Emulate design Emulate IP operation in FPGA In-system IP verification Cycle-level vs. transaction level test-bench

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Concluding… Main differences of SoC with ASIC design are

Planned IP-reuse Reuse of pre-verified platform Focus on co-verification with software

Newly added IP’s must be thoroughly verified before its application to SoC.

Well-established verification platform allows progressive verification/refinement of each IP, i.e., each SoC component while assuring correct implementation.

Powerful HW/SW co-simulation and co-debugging features are required.

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Thank you for your kind attention!