Design Considerations for USB Mass Storage

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Design

Considerations for

USB Mass Storage

Design

Considerations for

USB Mass Storage

Steve Kolokowsky

Cypress Semiconductor

syk

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Mass Storage – The Killer App

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Outline

Mass Storage ClassMass Storage Class

Bridge Selection CriteriaBridge Selection Criteria

–

– Fixed Function vs. Programmable BridgesFixed Function vs. Programmable Bridges

–

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Mass Storage Class

SCSI Command SetSCSI Command Set

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– RBC, Transparent, SFFRBC, Transparent, SFF--8070 subsets8070 subsets

Defines 13 possible combinations of host and Defines 13 possible combinations of host and device behavior

device behavior

Defines Bulk Only Transport (BOT) and Command _{Defines Bulk Only Transport (BOT) and Command} –

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Bulk Only Transport (BOT)

One IN and one OUT endpointOne IN and one OUT endpoint

CBW CBW ---- Data Data ---- CSWCSW

Uses STALL for Synchronization_{Uses STALL for Synchronization}

IN Pipe IN Pipe Control Pipe Control Pipe

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READ Transaction

CSW CSW Host Host Device Device OUT (CBW) OUT (CBW) "Read "Read Sectors" Sectors" ININ ININ Read Data Read Data

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Read Stall

OUT (CBW) OUT (CBW) "Read "Read Sectors" Sectors" STALL STALL IN IN SETUPSETUP Clear Stall Clear Stall CSW CSW w/ Residue w/ Residue Host Host Device Device IN IN

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Write Transaction

OUT (CBW) OUT (CBW) "Write (10)" "Write (10)" OUT OUT (DATA) (DATA) CSW CSW w/ Residue w/ Residue Device Device IN IN Host Host

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Write with STALL

OUT (CBW) OUT (CBW) "Write (10)" "Write (10)" CSW CSW w/ Residue w/ Residue Device Device IN IN Host Host STALL STALL OUT OUT (DATA) (DATA) SETUP SETUP Clear Stall Clear Stall

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Command Block Wrapper

(CBW)

Command Block Wrapper

(CBW)

Source – USB MSC BOT spec version 1.0 bit Byte 0-3 4-7 8-11 (08h-0Bh) 12 (0Ch) 13 (0Dh) 14 (0Eh) 15-30 (0Fh-1Eh) CBWCB Reserved (0) bCBWLUN Reserved (0) bCBWCBLength dCBWSignature dCBWTag dCBWDataTransferLength bmCBWFlags 3 2 1 0 7 6 5 4 bit Byte 0-3 4-7 8-11 (08h-0Bh) 12 (0Ch) 13 (0Dh) 14 (0Eh) 15-30 (0Fh-1Eh) CBWCB Reserved (0) bCBWLUN Reserved (0) bCBWCBLength dCBWSignature dCBWTag dCBWDataTransferLength bmCBWFlags 3 2 1 0 7 6 5 4

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Command Block (CBWCB)

READ Example

Command Block (CBWCB)

READ Example

bit Byte 0

1 DPO FUA RELADR

2 3 4 5 6 7 Reserved Reserved (MSB)

LOGICAL BLOCK ADDRESS (LSB) (MSB) Reserved OPERATION CODE (28h) 7 6 5 4 3 2 1 0 bit Byte 0

1 DPO FUA RELADR

2 3 4 5 6 7 Reserved Reserved (MSB)

LOGICAL BLOCK ADDRESS (LSB)

(MSB) Reserved

OPERATION CODE (28h)

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Command Status Word

(CSW) Contents

Command Status Word

(CSW) Contents

bit Byte 0-3 4-7 8-11 (08h-0Bh) 12 (Ch) dCSWDataResidue 0 dCSWSignature dCSWTag 4 3 2 1 bCSWStatus 7 6 5 bit Byte 0-3 4-7 8-11 (08h-0Bh) 12 (Ch) dCSWDataResidue 0 dCSWSignature dCSWTag 4 3 2 1 bCSWStatus 7 6 5

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Hn Hi Ho Dn (1) Hn = Dn (4) Hi > Dn (9) Ho > Dn (5) Hi > Di (6) Hi = Di (7) Hi < Di (11) Ho > Do HOST Di (2) Hn < Di (10) Ho <> Di D e v i Hn Hi Ho Dn (1) Hn = Dn (4) Hi > Dn (9) Ho > Dn (5) Hi > Di (6) Hi = Di (7) Hi < Di (11) Ho > Do HOST Di (2) Hn < Di (10) Ho <> Di D e v i c

The 13 Cases

Phase Error

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Host Support

Both Transports SupportedBoth Transports Supported

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– “Bulk Only” Transport (preferred)“Bulk Only” Transport (preferred)

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– “CBI” (Obsolete)“CBI” (Obsolete)

Supported by Microsoft (W2K, ME, XP)Supported by Microsoft (W2K, ME, XP)

Supported by Apple (OS9, OS X)_{Supported by Apple (OS9, OS X)}

Linux driver AvailableLinux driver Available

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OTG Support

Proposal for FAT16 under discussion.Proposal for FAT16 under discussion.

Implementations are ahead of the specImplementations are ahead of the spec

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– OTG Demo seen earlierOTG Demo seen earlier

Concerns about support for other devices_{Concerns about support for other devices}

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– CD/DVDCD/DVD

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Bridge Selection Criteria

All Bridge Chips are not Created EqualAll Bridge Chips are not Created Equal

ConsiderConsider – – PowerPower – – FlexibilityFlexibility – – TranslationTranslation – – SpeedSpeed

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Power

Some Mass Storage Class devices mustSome Mass Storage Class devices must be bus

be bus--poweredpowered

–

– Key chain drivesKey chain drives

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– Flash readersFlash readers

Most are notMost are not

–

– HDDHDD

–

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Programmable Vs Fixed

ATA Interface Solutions

Programmable Vs Fixed

ATA Interface Solutions

Fixed Function

Plug Plug –– n n –– PlayPlay

No changes_{No changes}

MaybeMaybe

Fixed performanceFixed performance

Programmable

Requires LearningRequires Learning

Custom Features_{Custom Features}

BIOS / OS supportBIOS / OS support

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Programmable

Device Benefits

Programmable

Device Benefits

Work With Non ATA compliant devicesWork With Non ATA compliant devices

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– Many optical drives are nonMany optical drives are non--compliant in subtle wayscompliant in subtle ways

Market DifferentiationMarket Differentiation

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– Add features beyond raw disk driveAdd features beyond raw disk drive

Special OS support_{Special OS support}

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– Support different spec variantsSupport different spec variants

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IDE Translation

The Class Spec only uses ATAPI commandsThe Class Spec only uses ATAPI commands

Translation required for nonTranslation required for non--ATAPI devicesATAPI devices

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– Hard DrivesHard Drives

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– Compact FlashCompact Flash

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– Embedded FlashEmbedded Flash

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– Other IDE devicesOther IDE devices

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Error Recovery

Errors are not “special cases”. They are a fact of Errors are not “special cases”. They are a fact of life for removable media

life for removable media

Error recovery strategiesError recovery strategies

Drive firmware errors_{Drive firmware errors}

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– Some may only be fixable by a programmable solutionSome may only be fixable by a programmable solution

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Speed

ATA Interface SpeedATA Interface Speed

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– UDMA/66 = 500MBits/secUDMA/66 = 500MBits/sec

BufferingBuffering

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– Larger buffers if no buffer on the driveLarger buffers if no buffer on the drive

Queuing Support_{Queuing Support}

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– Still undefined in the specStill undefined in the spec

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Driver Performance

System ConfigurationSystem Configuration

Software ConfigurationSoftware Configuration

Mass Storage Drivers Used_{Mass Storage Drivers Used}

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System Configuration

System TestedSystem Tested

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– P4 1.7Ghz, 128MBP4 1.7Ghz, 128MB

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– Windows XPWindows XP

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– Intel USB 2.0 Integrated Host Controller (ICH4)Intel USB 2.0 Integrated Host Controller (ICH4)

Test DevicesTest Devices

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– Cypress ISD300 ATA/ATAPI Bridge ChipCypress ISD300 ATA/ATAPI Bridge Chip

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– IBM DTLAIBM DTLA--307030 HD (30.7GB, 7200RPM)307030 HD (30.7GB, 7200RPM)

–

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Software Configuration

Software StackSoftware Stack

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– Intel Labs EHCI DriverIntel Labs EHCI Driver

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– Microsoft USB Mass Storage Class DriverMicrosoft USB Mass Storage Class Driver

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– Cypress USB Mass Storage Class DriverCypress USB Mass Storage Class Driver

Benchmark SoftwareBenchmark Software

–

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Software Configuration

Intel Labs ECHI Evaluation DriverIntel Labs ECHI Evaluation Driver

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– Custom ECHI driver developed by Intel LabsCustom ECHI driver developed by Intel Labs

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– Four different binaries used in Benchmark Comparisons:Four different binaries used in Benchmark Comparisons:

Compiled with Interrupt Threshold of 1 (ITH1) Compiled with Interrupt Threshold of 1 (ITH1) –– High priorityHigh priority

Compiled with Interrupt Threshold of 2 (ITH2)Compiled with Interrupt Threshold of 2 (ITH2)

Compiled with Interrupt Threshold of 4 (ITH4)Compiled with Interrupt Threshold of 4 (ITH4)

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Software Configuration

Microsoft USB Mass Storage Class DriverMicrosoft USB Mass Storage Class Driver

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– USB Storage Class driver included in the Windows XP USB Storage Class driver included in the Windows XP distribution

distribution

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– Used to obtain the results of a “Traditional” implementation of Used to obtain the results of a “Traditional” implementation of the USB Storage Class BOT specification

the USB Storage Class BOT specification

Cypress USB Mass Storage Class DriverCypress USB Mass Storage Class Driver

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“Traditional” Driver

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Performance Enhanced

Implementation

Performance Enhanced

Implementation

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USB 2.0 Benchmark

Comparisons

USB 2.0 Benchmark

Comparisons

Average Read Average Read Performance Performance

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– “Traditional” vs. Cypress “Traditional” vs. Cypress performance enhanced performance enhanced implementation, plus implementation, plus Native IDE Native IDE 0 5 10 15 20 25 30 M B P S

ITH8 ITH4 ITH2 ITH1 Native Microsoft USB Storage Class Driver Cypress USB Storage Class Driver Native IDE 0 5 10 15 20 25 30 M B P S

ITH8 ITH4 ITH2 ITH1 Native Microsoft USB Storage Class Driver Cypress USB Storage Class Driver Native IDE

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USB 2.0 Benchmark

Comparisons

USB 2.0 Benchmark

Comparisons

Average Write Average Write Performance Performance

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– “Traditional” vs. Cypress “Traditional” vs. Cypress performance enhanced performance enhanced implementation, plus implementation, plus Native IDE Native IDE 0 2 4 6 8 10 12 14 16 M B P S

ITH8 ITH2 Native

0 2 4 6 8 10 12 14 16 M B P S

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Summary

Mass Storage Class OverviewMass Storage Class Overview

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– BOT BOT –– Shared Interface for Commands and DataShared Interface for Commands and Data

Bridge SelectionBridge Selection

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– Programmable Solutions Allow CustomizationProgrammable Solutions Allow Customization