Functional Verification ofDynamically Reconfigurable Systems(Version 2.3b)

Mr. Lingkan (George) Gong, Dr. Oliver Diessel The University of New South Wales, Australia

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Outline

• Objectives & Motivation• Challenges in Verifying Dynamically

Reconfigurable Systems (DRS)• Proposed Solution: The ReSim Library• Example Designs• Conclusions

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Objectives & Motivation

• Dynamically Reconfigurable Systems (DRS)– Improved flexibility– Better resource utilization

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Objectives & Motivation• Functional Verification

– Bottleneck of all hardware designs– Most costly bugs occur in system integration stage– DRS designs Involve activities that don’t exist in static designs (e.g., module swapping, … )

• It is essential to perform simulation-based verification of Dynamically Reconfigurable Systems (DRS)1 bug/6 lines of RTL code

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Objectives & Motivation

• “Partial Reconfiguration itself can not be simulated … ”– Xilinx UG702 (Partial Reconfiguration User Guide) – Can simulate Static + A; Static +B; But not the process of

swapping out A and swapping in B

• Objective– Support the simulation of the reconfiguration process– Support the simulation and functional verification of integrated

Dynamically Reconfigurable Systems (DRS)

Dynamically ReconfigurableSystem (Static part)

Dynamic part:Module A

Dynamic part: Module B

Dynamic part:Module B

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Objectives & Motivation

• Focus on detecting functional bugs– e.g. Cycle mismatch– Assuming there is no timing violation, no errors in the bitstream,

no glitch in the reconfiguration process

• Focus on systematic verification– Correctly verified sub-systems, while necessary, are not sufficient– Recommend to simulate the design BEFORE running it on the

target device

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Challenges in Verifying DRS

• DRS-specific design considerations

Configuration Port (e.g. ICAP)

Configuration Memory

FPGA Fabric

User Design

application data

Staticmodule

Reconfigurablemodule B

Reconfigurablemodule A

bitstream transfer

bitstream data

potential trafficcontention Reconfigurable

module A

Reconfigurablemodule B

swap modulesaccording to the bitstreams

Disable , isolate, restart

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Challenges in Verifying DRS• DRS-specific bugs

– BEFORE Reconfiguration Handshake errors (e.g., deadlock) Fail to save module state …

– DURING Reconfiguration: Errors in bitstreams (e.g., if a design “assemble” bitstreams at run time, bugs can be introduced to the

generated bitstreams) Errors in transferring bitstreams (e.g., traffic contention, encryption …) Fail to isolate the module undergoing reconfiguration …

– AFTER Reconfiguration Errors in resetting the module Errors in state restoration …

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Challenges in Verifying DRS

• Accuracy v.s. Productivity– Simulation accuracy Modeling the entire FPGA fabric

Configuration Port (e.g. ICAP)

Configuration Memory

FPGA Fabric

User Design

application data

Staticmodule

Reconfigurablemodule B

Reconfigurablemodule A

bitstream data

Models for the FPGA fabric not available Even if available, it is not efficient to simulate the FPGA

fabric (Low Productivity)

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Challenges in Verifying DRS

• Accuracy v.s. Productivity– Simulation productivity DO NOT model the FPGA fabric

User Design

application data

Staticmodule

Reconfigurablemodule B

Reconfigurablemodule A

Does not model bitstream traffic Assume zero or constant reconfiguration delay Does not trigger module swapping Does not model spurious module outputs Low accuracy

??

??

????

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Challenges in Verifying DRS

• Accuracy v.s. Productivity– Simulation accuracy DO model the FPGA fabric– Simulation productivity DO NOT model the FPGA fabric

• It is essential to balance “accuracy” & “productivity” when simulating partial reconfiguration

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ReSim

• Core idea– Model the fabric at such a level of detail that is just

enough for RTL simulation of DRS

User Design

application data

Staticmodule

configuration_port : artifact

extended_portal:artifact

Simulation-only Layer

Reconfigurablemodule B

Reconfigurablemodule A

Simulation-only bitstream (SimB)

bitstream transfer

potential trafficcontention

switch moduleaccording to SimB

Errorsource

During reconfiguration, inject errors to the static region

"activate" the new module if and only if the all bytes of the bitstream is successful transferred

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ReSim

• Simulation-only bitstreams (SimB)– Capture the essence of a real bitstream, but with reduced

size

DRS_DESIGN_TOP

RR0

RM0

RM1

RR1 RM0 RM1 RM2 RM3

RR2 RM0

Module B

Module A

* Use module ID, region ID as Frame Address

* Use ReSim-specificfields as configurationdata

bottom-half

top-half

con

figu

rati

on c

olu

mn

configuration row

RA

CA

FPGA_FLOOR_PLAN

CLB

s

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ReSim• Capabilities and Limitations

– BEFORE Reconfiguration Handshake errors (e.g., deadlock) Fail to save module state …

– DURING Reconfiguration: Errors in bitstreams (e.g., if a design “assemble” bitstreams at run time, bugs can be introduced to the

generated bitstreams) Errors in transferring bitstreams (e.g., traffic contention, encryption …) Fail to isolate the module undergoing reconfiguration …

– AFTER Reconfiguration Errors in resetting the module Errors in state restoration …

RED: Only on Target deviceBLUE: Only by ReSimGRAY: More Efficient by ReSim

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ReSim

• Capabilities and Limitations– ReSim assists in testing fabric-independent part of the

design– After simulation, test & debug fabric-dependent part on

the target device (using Chipscope)

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ReSim

• Reusability– Codegen: automatic generation of artifacts– OO: override the default behavior of artifacts

CodeGeneration

HDL (VHDL/Verilog) Simulation-only Layer

(SystemVerilog)HDL (VHDL/Verilog)

Implementation using FPGA tools

FunctionalSpecification

Simulation using the ReSim library

.tcl script (parameter description file)

namespace import ReSim::*

# interface signalscreate_portmap "my_if" "clk"add_port "my_if" "rst_n" inadd_port "my_if" "data" out 32…# module namescreate_region "my_region" "my_if" ...add_module "my_region" "Maximum"add_module "my_region" "Swap"…# target device familycreate_device "my_device" VIRTEX4

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Example Designs

• Example Designs– XDRS.QUICKSTART– XDRS.SINGLE– XDRS.MULTIPLE– FPCIe– State_Migration

• Derived from ReSim case studies– See “ReSim Case Studies” for more information on development progress,

bugs detected and lessons learned.

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Example Design: XDRS

• XDRS: a generic DRS computing platform– Similar to Erlangen Slot Machine, a general-purpose

reconfigurable compute engine (Bobda et al. FCCM 2005)

Reconfigurable Region

Reconfiguration Controller: ICAPI

Producer

ICAP

Memory Interface

Isolation

application data

bitstream

reqn, ackn

Off-chip Memory

Maximum/Reverse

XDRS Specification (Partial Reconfiguration part) ======================== BEFORE Reconfiguration. (Synchronization) - use a reqn/ackn signals to handshake - not acknowledge until RM is IDLE

DURING Reconfiguration. (Isolation) - use an isolation module to drive default values to the static region

AFTER Reconfiguration. (Initialization) - reset the newly-configured RM

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Example Design: XDRS

• Example simulation waveform– @t1: Sync, @t2: Transfer a bitstream, @t3: Extract

RRID/RMID@t4: Inject errors, @t5: Swap module, @t6: Reset

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Example Design: XDRS

• Example bug that was detected– Hold the "reset" signal of a module during reconfiguration

producer_ready

consumer_ready

consumer_error

Module A/BProducer

producer_ready

consumer_ready

consumer_error

Isola

tion

producer_ready

consumer_ready

consumer_error

x

x

0

0

0

1

Normal operation:Transfer is successful

Normal operation:Transfer is cancelled

Bug 1:Outputs not isolated during reconfiguration

Bug 2:Transfer is not cancelled during reconfiguration

Correct:Assert consumer_error during reconfiguration

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Example Design: XDRS

• Regression and coverage analysis

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Example Design: FPCIe• FPCIe

– Derived from Fast PCIe configuration (XAPP883) ~3500 lines of Verilog code + Coregen code (the PCIe endpoint)

– Integrate ReSim with the original testbench 150 lines of Tcl script (120 IO signals) 10 lines of Verilog code to instantiate the generated artifacts 110 lines of Verilog code to send SimBs to the DUT

ICAPPR Loader

Sw

itch

er

Reconfigurable Region:

PCIe core application: Bus-master DMA

PCIe endpoint

Shared datapath betweenapplication data &bitstream data

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Example Design: FPCIe

• Example simulation waveform– @t1: Transfer a bitstream over PCIe, @t2: Swap module,

@t3: Application logic starts operating

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Example Design: State_Migration

• State_Migration– Derived from Microprocessor Peripheral reconfiguration

(UG744)– Modified the hardware to use PPC440 & xps_icapi– Modified the software to save RM state via ICAP

The modified software is composed of fabric-independent C code and fabric-dependent C code

xps_mathxps_icapi

DDR2 Memory

ICAP

Reconfigurable Region: Adder / Maximum

xps_uart

To host PC

microprocessor bus:PLBv46

PPC440microprocessor

periodic application

xps_math driverxps_icapi driver

ReSimVirtex-5

Software

SW: fabric-independent partSW: V5 & ReSim

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Example Design: State_Migration

• Example simulation waveform– @t1: Read ICAP IDCODE (ReSim’s IDCODE=0x0c1b2011)

@t2: Issue GCAPTURE@t3: Configuration readback

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Conclusions

• Accuracy v.s. Productivityproductivity

accuracy

High-level modelinge.g. C/C++/SystemC

RTL simulatione.g. Verilog/VHDL

Timing simulation(i.e., simulating the design netlist)

Fabric-accurate simulation(i.e., simulating the FPGA fabric)

+

+

+x

x

ReChannelOSSS+R

VMUXDCS

x

+ Static designs

x DRS designs

xReSim

ReSim is - more productive than fabric-accurate simulation- more accurate than MUX-based simulation

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Conclusions

• It is essential to simulate partial reconfiguration– Activities such as bitstream traffic, triggering condition, state saving and restoration,

isolation of the reconfigurable region, …

• It is essential to balance accuracy & productivity– Modeling the FPGA fabric is not productive– MUX-based simulation is not accurate

• ReSim– Models the fabric at such a level of detail that is just enough for RTL simulation of DRS– A reusable simulation library

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More Infomation

• ReSim Home Page– http://code.google.com/p/resim-simulating-partial-reconfiguration/

• ReSim Document– ReSim User Guide– ReSim Case Studies

• Contact– Mr. Lingkan Gong,

http://code.google.com/p/resim-simulating-partial-reconfiguration/wiki/Lingkan_Gong – Dr. Oliver Diessel, http://www.cse.unsw.edu.au/~odiessel/

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Thank you