Processes, interfaces and Processes, interfaces and platforms.platforms.Embedded software modeling in Embedded software modeling in Metropolis.Metropolis.

Luciano LavagnoLuciano Lavagno

Politecnico di TorinoPolitecnico di Torino

EMSOFT 2002, CASES 2002EMSOFT 2002, CASES 2002

Grenoble, FranceGrenoble, France

Metropolis Project: main participantsMetropolis Project: main participants

Cadence Berkeley Labs Cadence Berkeley Labs (USA): (USA): methodologiesmethodologies, , modelingmodeling, , formal formal methodsmethods

UC BerkeleyUC Berkeley (USA): (USA): methodologiesmethodologies, , modelingmodeling, , formal methodsformal methods Politecnico di TorinoPolitecnico di Torino (Italy): (Italy): modelingmodeling, , formal methodsformal methods Universitat Politecnica de CatalunyaUniversitat Politecnica de Catalunya (Spain): (Spain): modelingmodeling, , formal methodsformal methods Philips ResearchPhilips Research (Netherlands): (Netherlands): methodologiesmethodologies (multi-media) (multi-media) NokiaNokia (USA, Finland): (USA, Finland): methodologiesmethodologies (wireless communication) (wireless communication) BWRCBWRC (USA): (USA): methodologiesmethodologies (wireless communication) (wireless communication) BMWBMW (USA): (USA): methodologiesmethodologies (fault-tolerant automotive controls) (fault-tolerant automotive controls) IntelIntel (USA): (USA): methodologiesmethodologies (microprocessors) (microprocessors) STMicroelectronicsSTMicroelectronics (France, Italy): (France, Italy): methodologiesmethodologies (wireless platforms) (wireless platforms)

etropolis

Metropolis FrameworkMetropolis Framework

Infrastructure

• Metropolis meta-model

- language

- modeling mechanisms• Meta-model compiler

Meta-model Library

• Models of computation

Meta-model Library

• Architecture platforms

Tools

Simulator QSS PIG STARS SPIN …

Application-specific methodologies

Multi-media, wireless communication, mechanical controls, processors

Design MethodologyDesign Methodology

Balance between reusability and optimalityBalance between reusability and optimality orthogonalize design concerns as much as possibleorthogonalize design concerns as much as possible

optimize the final implementation as much as necessaryoptimize the final implementation as much as necessary

RefineOptimize

Implementationof System

Functional& Non-func.Constraints

FunctionComponent

LibraryMPEG

decodePES

parser VSRCI$ D$

CPU UART RTOS

ArchitectureComponent

Library

demux PESparser

MPEGdecode HSRC VSRC

ImageJuggler

MPEGdecode

Control

SystemFunction

Model

SystemArchitecture

Model

BCU

HWassist MEM

I$ D$

CPU UARTINT

RTOS APIdriver

Map

Metropolis meta-modelMetropolis meta-model

• Computation : f : X Z

• Communication : state evaluation and manipulation

• Coordination : constraints over concurrent actions

- process : generates a sequence of events

- medium : defines states and methods

- quantity : annotation of each event (time, energy, memory, …)

- logic : relates events and quantities, defines axioms on quantities

- quantity-manager : algorithm to realize annotation subject to relational constraints

Concurrent specification with a formal execution semantics:

Key difference with respect to Ptolemy, UML, SystemC, …!!!

Concurrent specification with a formal execution semantics:

Meta-model : function netlistMeta-model : function netlist

process P{

port reader X;

port writer Y;

thread(){

while(true){

...

z = f(X.read());

Y.write(z);

}}}

medium M implements reader, writer{

int storage;

int n, space;

void write(int z){

await(space>0; writer ; writer)

n=1; space=0; storage=z;

}

word read(){ ... }

}

interface reader extends Port{

update int read();

eval int n();

}

interface writer extends Port{

update void write(int i);

eval int space();

}

MP1X Y P2X Y

Env1 Env2

MyFncNetlist

R

I

F A

M

Meta-model: execution semanticsMeta-model: execution semantics

Processes take actions. statements and some expressions, e.g.

y = z+port.f(), port.f(), i < 10, …

An execution of a given netlist is a sequence of vectors of events. event : the beginning of an action, e.g. B(port.f()),

the end of an action, e.g. E(port.f()),

null (no-op) N the i-th component of a vector is an event of the i-th process synchronous trace-based semantics time and other quantities elapse and actions are executed in states no assumption on atomicity whatsoever (unless explicitly modeled)

An execution is feasible if it satisfies all coordination constraints, and it is accepted by all action automata defining meta-model semantics

Meta-model: architecture componentsMeta-model: architecture componentsAn architecture component specifies services, i.e.

• what it can do

• how much it costs

: interfaces

: quantities, annotation, logic of constraints

medium Bus implements BusMasterService …{

port BusArbiterService Arb;

port MemService Mem; …

update void busRead(String dest, int size) {

if(dest== … ) Mem.memRead(size);

[[Arb.request(B(busRead));

GTime.request(B(memRead),

BUSCLKCYCLE +

GTime.annotation(B(busRead)));

]]

}

…

scheduler BusArbiter extends Quantity

implements BusArbiterService {

update void request(event e){ … }

update void resolve() { //schedule }

}

interface BusMasterService extends Port {

update void busRead(String dest, int size);

update void busWrite(String dest, int size);

}

interface BusArbiterService extends Port {

update void request(event e);

update void resolve();

}

BusArbiterBus

R

I

F A

M

Meta-model: architecture netlist Meta-model: architecture netlist

Bus

ArbiterBus

Mem

Cpu OsSched

MyArchNetlist

…

…

…

Master

CPU + OS

Slave

Mem

Arbiter

Architecture netlist specifies configurations of architecture components.

Each constructor

- instantiates arch. components,

- connects them,

- takes as input mapping processes.

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I

F A

M

Meta-model: mapping processesMeta-model: mapping processes

process P{

port reader X;

port writer Y;

thread(){

while(true){

...

z = f(X.read());

Y.write(z);

}}

int f (int n) {

int i;

for (i = 0; i < n; i++) {

…

}}

process MapP{

port CpuService Cpu;

void readCpu(){

Cpu.exec(2); Cpu.cpuRead();

}

void mapf(){Cpu.exec(12*n); } …

}

thread(){

while(true){

await {

(true; ; ;) readCpu();

(true; ; ;) mapf();

(true; ; ;) readWrite();

}}}

B(P, X.read) <=> B(MapP, readCpu); E(P, X.read) <=> E(MapP, readCpu);

B(P, f) <=> B(MapP, mapf); E(P, f) <=> E(MapP, mapf);…

Function process Mapping process

R

I

F A

M

Meta-model: mapping netlistMeta-model: mapping netlist

Bus

ArbiterBus

Mem

Cpu OsSched

MyArchNetlist

mP1 mP2mP1 mP2

MyFncNetlist

MP1 P2

Env1 Env2

B(P1, M.write) <=> B(mP1, mP1.writeCpu); E(P1, M.write) <=> E(mP1, mP1.writeCpu);

B(P1, P1.f) <=> B(mP1, mP1.mapf); E(P1, P1.f) <=> E(mP1, mP1.mapf);

B(P2, M.read) <=> B(P2, mP2.readCpu); E(P2, M.read) <=> E(mP2, mP2.readCpu);

B(P2, P2.f) <=> B(mP2, mP2.mapf); E(P2, P2.f) <=> E(mP2, mP2.mapf);

MyMapNetlist

Bus

ArbiterBus

Mem

Cpu OsSched

MyArchNetlist…

……

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I

F A

M

Meta-model: platformsMeta-model: platforms

interface MyService extends Port { int myService(int d); }

medium AbsM implements MyService{ int myService(int d) { … }}

B(thisthread, AbsM.myService) <=> B(P1, M.read);

E(thisthread, AbsM.myService) <=> E(P2, M.write);refine(AbsM, MyMapNetlist);

MyArchNetlistMyFncNetlist MP1 P2

B(P1, M.write) <=> B(mP1, mP1.writeCpu); B(P1, P1.f) <=> B(mP1, mP1.mapf); E(P1, P1.f) <=> E(mP1, )B(P2, M.read) <=> B(P2, mP2.readCpu); E(P2, P2.f) <=> E(mP2, mP2.mapf);

MyMapNetlist1

MyArchNetlistMyFncNetlist MP1 P2

B(P1, M.write) <=> B(mP1, mP1.writeCpu); B(P1, P1.f) <=> B(mP1, mP1.mapf); E(P1, P1.f) <=> E(mP1, )B(P2, M.read) <=> B(P2, mP2.readCpu); E(P2, P2.f) <=> E(mP2, mP2.mapf);

MyMapNetlist1

B(…) <=> B(…);

E(…) <=> E(…);refine(AbsM, MyMapNetlist1)

MyArchNetlistMyFncNetlist

MP1 P2

B(P1, M.write) <=> B(mP1, mP1.writeCpu); B(P1, P1.f) <=> B(mP1, mP1.mapf); E(P1, P1.f) <=> E(mP1, )B(P2, M.read) <=> B(P2, mP2.readCpu); E(P2, P2.f) <=> E(mP2, mP2.mapf);

MyMapNetlist2

M

B(…) <=> B(…);

E(…) <=> E(…);

refine(AbsM, MyMapNetlist2)

A set of mapping netlists, together with constraints on event mappings, constitutes a platform (constrained set of possible implementations) with a given interface.

R

I

F A

M

R

I

F A

M

Meta-model: recursive platformsMeta-model: recursive platforms

S

N N'

B(Q2, S.cdx) <=> B(Q2, mQ2.excCpu); E(Q2, M.cdx) <=> E(mQ2, mQ2.excCpu);

B(Q2, Q2.f) <=> B(mQ2, mQ2.mapf); E(Q2, P2.f) <=> E(mQ2, mQ2.mapf);

MyArchNetlistMyFncNetlist MP1 P2

B(P1, M.write) <=> B(mP1, mP1.writeCpu); B(P1, P1.f) <=> B(mP1, mP1.mapf); E(P1, P1.f) <=> E(mP1, )B(P2, M.read) <=> B(P2, mP2.readCpu); E(P2, P2.f) <=> E(mP2, mP2.mapf);

RTOSNetlist

MyArchNetlist

MyFncNetlist

MP1 P2B(P2, M.read) <=> B(P2, mP2.readCpu); E(P2, P2.f) <=> E(mP2, mP2.mapf);

M

RTOS

Meta-model: summaryMeta-model: summary

• Concurrent specification with a formal execution semantics

• Feasible executions of a netlist: sequences of event vectors

• Quantities can be defined and annotated with events, e.g.

time, energy, memory, ...

• Concurrent events can be coordinated in terms of quantities:

- logic can be used to define the coordination,

- algorithms can be used to implement the coordination.

• The mechanism of event coordination wrt quantities plays a key role:

- architecture modeling as service with cost,

- mapping coordinates executions of functional and architecture netlists,

- refinement with event coordination provides a platform.

Metropolis FrameworkMetropolis Framework

Infrastructure

• Metropolis meta-model

- language

- modeling mechanisms• Meta-model compiler

Meta-model Library

• Models of computation

Meta-model Library

• Architecture platforms

Tools

Simulator QSS PIG STARS SPIN …

Application-specific methodologies

Multi-media, wireless communication, mechanical controls, processors

Metropolis infrastructure architectureMetropolis infrastructure architecture

Meta model compiler

Verification tool

Verification tool

Front end

Meta model language

Simulator tool

...Back end1

Abstract syntax trees

Back end2 Back endNBack end3

Synthesis tool

Language1 Language2 Languagen

Translator1 Translator2 Translatorn...

Metropolis infrastructure statusMetropolis infrastructure status

Meta model compiler

SpinPrometheus

Front end

Meta model language

SystemCSimulator

...Back end1

Abstract syntax trees

Back end2 Back endNBack end3

Symbolic HW

scheduler

Simulink Esterel/Lustre UML

Translator1 Translator2 Translatorn...

Deriving other formal models from the meta-modelDeriving other formal models from the meta-model

Example: Petri nets

await(X.n()>=2; X.reader; X.reader)

for(i=0; i<2; i++) x[i]=X.read();

reader_unlock

reader_lockX.n()

2

2

i=0;

i<2?

x[i]=X.read();i++;

end of await

Formal methods on Petri nets:

• analyze the schedulability

• analyze upper bounds of storage sizes

• synthesize schedules

Restrictions:

•condition inside await is conjunctive

•specific medium type (FIFO) is used

Example: quasi-static schedulingExample: quasi-static scheduling

1 Specify a network of processesSpecify a network of processes

2 Translate to the Petri net modelTranslate to the Petri net model

3 Find a “schedule” on the Petri netFind a “schedule” on the Petri net

4 Translate the schedule to a set of tasks Translate the schedule to a set of tasks

(processes)(processes)

Metropolis SummaryMetropolis Summary

• Metropolis meta-model:

- concurrent specification for functions, architecture, and mappings

- libraries of models of computation, libraries of platforms

• Metropolis design environment:

- meta-model compiler to provide an API to browse designs,

- backend tools to analyze designs and produce appropriate models,

- easy to incorporate simulation, verification, and synthesis tools

Backup slides: Execution semanticsBackup slides: Execution semantics

A sequence of vectors of events is a legal behavior A sequence of vectors of events is a legal behavior

if itif it satisfies all constraintssatisfies all constraints

is accepted by all is accepted by all action automataaction automata one for each action of each processone for each action of each process

B y=x+1

Action automataAction automata

y=x+1;y=x+1;B y=x+1 B x+1 E x+1 E y=x+1

y:=Vx+1

B x+1 E x+1 E y=x+1y:=any

c

c

c

c

* = write y* * *

B x+1 E x+1Vx+1 :=x+1

E x+1Vx+1 :=any

c

c

write x

y=x+1

x+1

Vx+1

yx

000

N

Action automataAction automata

y=x+1;y=x+1;

y=x+1

x+1

Vx+1

yx

B y=x+1 B x+1 E x+1 E y=x+1y:=Vx+1

B x+1 E x+1 E y=x+1y:=any

c

c

c

c

* = write y* * *

B x+1 E x+1Vx+1 :=x+1

E x+1Vx+1 :=any

c

c

write x

000

B y=x+1 B x+1 NN N

E x+1

100

Action automataAction automata

y=x+1;y=x+1;

y=x+1

x+1

Vx+1

yx

B y=x+1 B x+1 E x+1 E y=x+1y:=Vx+1

B x+1 E x+1 E y=x+1y:=any

c

c

c

c

* = write y* * *

B x+1 E x+1Vx+1 :=x+1

E x+1Vx+1 :=any

c

c

write x

000

B y=x+1 B x+1 NN N

Action automataAction automata

y=x+1;y=x+1;

y=x+1

x+1

Vx+1

yx

B y=x+1 B x+1 E x+1 E y=x+1y:=Vx+1

B x+1 E x+1 E y=x+1y:=any

c

c

c

c

* = write y* * *

B x+1 E x+1Vx+1 :=x+1

E x+1Vx+1 :=any

c

c

write x

000

B y=x+1 B x+1 E x+1NN N E y=x+1

100

110

B y=x+1

Action automataAction automata

y=x+1;y=x+1;

y=x+1

x+1

Vx+1

yx

B y=x+1 B x+1 E x+1 E y=x+1y:=Vx+1

B x+1 E x+1 E y=x+1y:=any

c

c

c

c

* = write y* * *

B x+1 E x+1Vx+1 :=x+1

E x+1Vx+1 :=any

c

c

write x

000

N

Action automataAction automata

y=x+1;y=x+1;

y=x+1

x+1

Vx+1

yx

B y=x+1 B x+1 E x+1 E y=x+1y:=Vx+1

B x+1 E x+1 E y=x+1y:=any

c

c

c

c

* = write y* * *

B x+1 E x+1Vx+1 :=x+1

E x+1Vx+1 :=any

c

c

write x

000

B y=x+1 B x+1 NN

Action automataAction automata

y=x+1;y=x+1;

y=x+1

x+1

Vx+1

yx

B y=x+1 B x+1 E x+1 E y=x+1y:=Vx+1

B x+1 E x+1 E y=x+1y:=any

c

c

c

c

* = write y* * *

B x+1 E x+1Vx+1 :=x+1

E x+1Vx+1 :=any

c

c

write x

000

B y=x+1 B x+1 NN N

E x+1

500

Action automataAction automata

y=x+1;y=x+1;

y=x+1

x+1

Vx+1

yx

B y=x+1 B x+1 E x+1 E y=x+1y:=Vx+1

B x+1 E x+1 E y=x+1y:=any

c

c

c

c

* = write y* * *

B x+1 E x+1Vx+1 :=x+1

E x+1Vx+1 :=any

c

c

write x

000

B y=x+1 B x+1 NN N

Action automataAction automata

y=x+1;y=x+1;

y=x+1

x+1

Vx+1

yx

B y=x+1 B x+1 E x+1 E y=x+1y:=Vx+1

B x+1 E x+1 E y=x+1y:=any

c

c

c

c

* = write y* * *

B x+1 E x+1Vx+1 :=x+1

E x+1Vx+1 :=any

c

c

write x

000

B y=x+1 B x+1 E x+1NN N E y=x+1

500

550

Semantics of awaitSemantics of await

await {await { (X.n()>0;X.writer; X.writer) comp: z = f(X.read());(X.n()>0;X.writer; X.writer) comp: z = f(X.read()); (Y.space()>0;Y.reader;Y.reader) Y.write(z);(Y.space()>0;Y.reader;Y.reader) Y.write(z);}}

B await...c start Y.reader

E comp:...(true X.n()>0 active X.writer)/

B comp:...

(true Y.space()>0 active Y.reader) / B Y.write(z)

E Y.write(z)

start X.writer

cE await...

Semantics summarySemantics summary

Processes run sequential code concurrently, each at its Processes run sequential code concurrently, each at its

own arbitrary paceown arbitrary pace

Read-Write and Write-Write hazards may cause Read-Write and Write-Write hazards may cause

unpredictable resultsunpredictable results

atomicity has to be explicitly specifiedatomicity has to be explicitly specified

Progress may block at synchronization pointsProgress may block at synchronization points

awaitsawaits

function calls and labels to which awaits or LTL function calls and labels to which awaits or LTL constraints referconstraints refer