Methodologies and flows for chip design

Methodologies and flows for chip design

Chip Specification Language (CSL)

Derek Pappas

Overview

Shared infrastructure

• Infrastructure elements are shared between teams

• Infrastructure elements include hierarchies,

connections, vectors, vector readers/writers, state

elements (e.g. registers, register files, …), ISA’s,

pipelines, address maps, …

• Infrastructure elements do not include

• Control and data path elements which are typically

implemented differently in RTL and simulation

The cost of not automating vs automating

• Failing to automate the generation of infrastructure

code costs companies $$$’s and increases time to

market

• Conversely a significant reduction in engineering and

verification time can be achieved by automating the

infrastructure generation process

Infrastructure changes

• Changes in the architecture and RTL cause changes in

simulation, verification, documentation, and software

• Manually generated infrastructure is time consuming to

maintain

• Manually generated infrastructure limits the number of

verification points/test benches on projects

• Teams should not spend time creating and maintaining

infrastructure when the infrastructure can be generated

Infrastructure changes (continued)

• Changes in infrastructure are communicated through

emails, meetings, build breaks, and tickets

• Often documentation is not updated to reflect the

infrastructure changes

Throwing problems over the wall

• Throwing problems over the wall gives the illusion that

the generation of infrastructure in one domain can be

done quickly

• The next domain has to reimplement the same

infrastructure elements

• The changes have to be made in all domains

Problem: Parallel bookkeeping

• Eliminate the parallel bookkeeping required to

synchronize shared infrastructure elements between

teams

Automatically generate shared infrastructure

• 100x reduction in code

• Rapidly bring up the project

• Rapidly make changes

• Propagate changes to all affected parties

HW/SW/Simulation/Verification interface

methodology

HW SW

Verif Sim

Equivalent infrastructure across all file views/teams

with documentation

DOCS

Shared infrastructure

• Examples:

• Interfaces

• Registers

• Vectors

CSL infrastructure generation flow

CSL specification

HW SWVerif Sim DOCS

CSL compiler

Reduce integration time

• Tighter software/hardware integration

• Tighter simulation/hardware integration

• Tighter test/simulation/hardware integration

Benefits

• Rapidly bring up test benches, simulation and design

• Test RTL from day 1

• Spend time on the architecture and design

• No time wasted bringing up and maintaining

infrastructure

• 10-100x reduction in work required to create the project

infrastructure

Benefits (continued)

• Generate infrastructure code and documentation which

is in sync

• Create a specification for infrastructure which can be

compiled

• Cloud based team solution (to be built) for instant

collaboration using a GUI and table driven entry

• To be constructed using the existing C++ class

hierarchy and compiler, with web based tools and an

underlying database

Benefits (continued)

• Extensive CSL documentation (manuals)

• Need to be converted from Framemaker which is no

longer supported by Adobe

• CSL is throughly tested

• Automatic and manual test suites

• Regression/reports

• Needs to be turned into a web based report and run on

a continuous integration server like Jenkins

Dramatically increase the number of verification

points

• A verification point in an RTL design is either set of

interfaces or state that is driven by stimulus vectors and

compared expected vectors and/or state from an

alternate implementation’s

• Teams are bandwidth limited when creating verification

points in designs

• Creation and maintenance of test infrastructure is time

consuming

Typical objections to infrastructure meta

languages and compilers

Typical objections by HW engineers to using

meta specification languages

• “I can write the infrastructure code as fast as writing

meta language spec”

• No one can write code as accurately as a working

compiler can.

• “I only write the infrastructure code once”

• Infrastructure code changes and needs to be synced

across domains


meta specification languages (continued)

• “Integration does not take long so I do not need a meta specification

language/GUI/compiler”

• Integration lasts for an entire project cycle and if the entire design has

complete coverage with respect to test points it will take an army of

verification engineers to generate the test benches.

• “Integration does not take long so I do not need a meta specification

language/GUI/compiler”

• Integration accounts for a huge amount of delays on projects. We

Brought up 64 processor application specific chips at Sun in 2 weeks,

including a basic compiler and RTL model in under 3 weeks using a

meta language to generate the complex interconnect for the entire

chip in 2 days.



• “Generated code is not flexible and I can’t add custom

code to it”

• Wrong. Generated code has points where custom

code can be inserted to modify the behavior of the

design

• “No one uses tools to do that…”

• Hardware engineers who do not not embrace well

understood software engineering principles reject

meta language compilers



• “We already have point tools for memory map

generation, interconnect generation”

• The individual tools typically do not communicate with

one another and parts of the infrastructure

specification needs to be replicated in each of the

overlapping tool’s input format.

• “We have SystemC/System Verilog“

• These are not meta description languages

The Objections are not factual…

• In reality no programmer can create or maintain large

pieces of infrastructure code on a project

• Infrastructure code needs to be consistent across

different views which is not possible with “parallel book

keeping”

• It takes a lot longer to manually create and maintain

infrastructure code than it does to write a compressed

representation in a meta language and/or to use a GUI

to describe the specification and to compile the

specification

Meta specification language

Guaranteeing consistency between different

views

• A single source is used to describe the shared

infrastructure

• A single source eliminates parallel bookkeeping

problems

Automating the chip specification process

• A meta level specification is constructed using a GUI

and the Chip Specification Language (CSL)

• The CSL specification is checked for correctness by

software

• Generation of shared infrastructure code for RTL,

simulation, software, and verification

CSL Grammar/ENF

• CSL is well defined

• The language is parsed using ANTLR

Meta specification language benefits

• Single source

• Rapid changes

• Synchronization of changes across all domains

• Minimal time to infrastructure

• Minimal code set

Requirements for a meta specification language

• Different domains share infrastructure

• Need an unambiguous shared specification

• The specification should compile

CSL Language

CSL Attributes

• CSL is object oriented

• CSL is similar to C++/Java

• No pointers/memory management

• Scopes

• CSL is easy to learn

CSL Documentation

• CSL grammar is specified for each major component

(e.g. interconnect, test benches, …)

• Examples for each language construct are shown

• CSL code + diagrams + generated Verilog/C++

Interconnect, hierarchy and test

benches

Connections

Connection types

• Scalar

• Vector

• Concatenations

• Structures

• Hierarchies

Signal types

• [SLIDES UNDER CONSTRUCTION]

Aggregated structures

• [SLIDES UNDER CONSTRUCTION]

Connections and functional units


Hierarchies and pipelines

a0_0[9:0]

b0_0[9:0]

c0_0[9:0]

d0_0[9:0]

a1_0[9:0]

b1_0[9:0]

c1_0[9:0]

d1_0[9:0]

a0_1[9:0]

b0_1[9:0]

c0_1[9:0]

d0_1[9:0]

a1_1[9:0]

b1_1[9:0]

c1_1[9:0]

d1_1[9:0]

x{x0}

x{x1}

y

x{x0}

x{x1}

y

x{x0}

x{x1}

y

z{z2}z{z0} z{z1}

top

Auto routing connections between end points

• End points, name(s), and the type to route are specified

• Intermediate connections do not need to be specified

• Benefits

• Consistency between different file views

• Rapid floor planning changes to meet full chip timing


a[9:0]b[9:0]c9:0]d[9:0]

Signal Group

abcd

Connections

z{z0}.y.x{x0} ->

abcd

-> z{z1}.y.x{x0}

Hierarchy

x{x0} x{x1} x{x1} x{x1} x{x1} x{x1}

y y

top

y

z{z0} z{z1} z{z2}

Connections are autoroutes across hierarchies

Tech bench generation

C/C++/SystemC Simulator

infrastructure generation

Generation of simulator infrastructure code

• Simulator code is generated from the meta specification

• Equivalent verification points are chosen between the

RTL design and simulator

• Vector writers/readers are generated automatically

• Vector readers/writers are generated in the

corresponding test benches

Automatic simulator infrastructure generation

benefits

• The simulator infrastructure code is updated

automatically

• The generated infrastructure infrastructure in the

simulator is in sync with the corresponding

infrastructure elements in different domains (i.e. RTL,

software, verification)

Automatic test bench generation

• Maintain consistency between the RTL design unit

under test (DUT), the algorithmic or cycle based

simulator, tests, and test benches

• Generate test benches at every level

• The generation of infrastructure for test bench

generation/design coverage is not limited by the

bandwidth of the design, simulation, and verification

teams

Level of verification detail

• Creating test benches

• Integration of multiple units

• Leaf level testing

• Lots to maintain

Connections (signals) become vectors

• Consistency between the design, the simulator and the

test bench is maintained

Different levels of abstraction in models

C++ simulator

uint abcd1

uint abcd0

uint abcd1

uint abcd0

a1_0[9:0]

b1_0[9:0]

c1_0[9:0]

d1_0[9:0]

a1_1[9:0]

b1_1[9:0]

c1_1[9:0]

d1_1[9:0]v

==

RTL test bench

Infrastructure equivalency requirement

uint abcd1

uint abcd0

uint abcd1

uint abcd0

a1_0[9:0]

b1_0[9:0]

c1_0[9:0]

d1_0[9:0]

a1_1[9:0]

b1_1[9:0]

c1_1[9:0]

d1_1[9:0]v

==

Input vector Expected vector

Module under test instantiation

Vector checkerVector reader

Inter unit

ConnectionsOutputs

Design hierarchy

Inputs

OutputsInputs

Inter unit Connections

C++ simulator

RTL test bench

Infrastructure maintenance/parallel book keeping

• Single test bench

• At least 7 infrastructure elements to maintain

• Different teams needs to keep in sync

• Changes break regressions/tests

Deign hierarchy equivalency-verification point

uint abcd1

uint abcd0

uint abcd1

uint abcd0

a1_0[9:0]

b1_0[9:0]

c1_0[9:0]

d1_0[9:0]

a1_1[9:0]

b1_1[9:0]

c1_1[9:0]

d1_1[9:0]v

==

C++ simulator

RTL test bench

Design hierarchy

Unit interface equivalency

uint abcd1

uint abcd0

uint abcd1

uint abcd0

a1_0[9:0]

b1_0[9:0]

c1_0[9:0]

d1_0[9:0]

a1_1[9:0]

b1_1[9:0]

c1_1[9:0]

d1_1[9:0]v

==

OutputsInputs

OutputsInputs

C++ simulator

RTL test bench

Vector equivalency

uint abcd1

uint abcd0

uint abcd1

uint abcd0

a1_0[9:0]

b1_0[9:0]

c1_0[9:0]

d1_0[9:0]

a1_1[9:0]

b1_1[9:0]

c1_1[9:0]

d1_1[9:0]v

==


C++ simulator

RTL test bench

Test bench generation

uint abcd1

uint abcd0

uint abcd1

uint abcd0

a1_0[9:0]

b1_0[9:0]

c1_0[9:0]

d1_0[9:0]

a1_1[9:0]

b1_1[9:0]

c1_1[9:0]

d1_1[9:0]v

==

Module under test instantiation

Vector checkerVector reader

Inter unit Connections

C++ simulator

RTL test bench

State infrastructure/registers

C++ simulator

uint abcd1

uint abcd0

uint abcd1

uint abcd0

a1_0[9:0]

b1_0[9:0]

c1_0[9:0]

d1_0[9:0]

a1_1[9:0]

b1_1[9:0]

c1_1[9:0]

d1_1[9:0]v

==

RTL test bench

RF

RF

==

Input vector

Expected vectorComparator

Standalone algorithmic simulators can be built to

generate vectors

uint abcd1uint abcd1

a1_0[9:0]

b1_0[9:0]

c1_0[9:0]

d1_0[9:0]

a1_1[9:0]

b1_1[9:0]

c1_1[9:0]

d1_1[9:0]v

==


Stand

alone

software

simulator

RTL test bench

test(s)

Signal Inheritance

Objects share features

• The same bits are reused in different types of objects

• Connections

• Inputs/outputs

• Registers

• Pipelines

• Vectors

Reuse of features

• Objects inherit features from a meta description

• All derived objects share the same features

Reuse benefits

• Reuse reduces time to code

• Reuse reduces errors

• Reuse eliminates parallel book keeping

• Reuse reduces time to make changes

Example: pipeline connected to a signal

opcode_0[3:0]

srca_0[5:0]

srcb_0[5:0]

dest_0[5:0]

opcode_0[3:0]

srca_0[5:0]

srcb_0[5:0]

dest_0[5:0]

opcode_0[3:0]

srca_0[5:0]

srcb_0[5:0]

dest_0[5:0]

v

valid

sta

ll

reset

enable

instruction_0[21:0] instruction[21:0]

v

valid

sta

ll

reset

enable

instruction_0[21:0]

opcode[3:0]

srca[5:0]

srcb[5:0]

dest[5:0]

instruction[21:0]

Access elements in aggregated structures

instruction[21:0]

instruction.srca

instruction.srcb

instruction.dest

Memory maps

Memory maps (CSL under construction)

• The CSL memory map specification integrates tightly

with the other CSL components

Pipeline Generation

Generating pipelines (under construction)

• Generation of pipeline code can eliminate register over

and under run errors

• Valid, stall, and enable logic is generated

• Cookie cutter/cut and paste pipeline logic is generated

• Pipeline naming conventions are followed and names

are updated automatically

Control, Status, Query,

configure, Measure

Control, Status, Query, Configure, Measure

• Control

• Status

Out of band communication

• [UNDER CONSTRUCTION]

Non-shared infrastructure elements

• Non-shared infrastructure elements which need to integrate with RTL

for tape out models which can be generated from a specification

• Clock trees

• Testability logic

• IO pads

• Note: it can be argued that most of this logic should be int he RTL

design

• Some design teams “hack” the clock trees and testability logic into

the netlist which further delays takeout instead of putting the clock

trees and testability logic under test/regression control

More CSL components

• The CSL language is very comprehensive

• Many more CSL components are supported by the CSL

compiler and documented.

• Some components need to be built out

Engineering

Methodologies and flows for chip design