A DSP-Based Platform for Wireless Video Compression

Patrick Murphy, Vinay Bharadwaj,

Erik Welsh & J. Patrick Frantz

Rice University

November 18, 2002

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Motivations & Requirements

• Wireless video communication• Demand expected to explode• Much more challenging than voice

• Standards not yet established• Need modular hardware & software

• Testbed should approximate real system• Similar hardware• Portable code

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Testbed Description• Source coding on Texas Instruments DSP• Similar to processors in most wireless devices

• Mature software development environment• Bluetooth wireless interface• Datarate comparable to future mobile systems

• Decoding performed on separate PC

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Testbed Hardware• Custom hardware• Inspired by TI Imaging Developers Kit• Support for lower resolution imaging• Integrates wireless interface & host processor

• Daughtercard to TI DSP Starter Kits• Adheres to DSK interface specification• Backward and forward compatible with DSKs

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Testbed Hardware

Custom daughtercard on C6416 DSP board

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Hardware Details: Processor

• Axis Etrax 100LX• 32-bit 100 MIPS RISC processor• Runs full Linux operating system

• Uses 2.4.x kernels and glibc• Open source Bluetooth stack

• Originally developed by Axis• Now available under GPL

• Multichip Module• Integrated flash, SDRAM and Ethernet interface

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Hardware Details: Camera• Omnivision CMOS imager• 16-bit digital interface• Supports YUV 4:2:2 and raw RGB• On-board image preprocessor

• Color space conversion• White balance

• Configuration by I2C• Easily controlled by Etrax processor

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Hardware Details: Bluetooth

• Support for variety of Bluetooth hardware• Up to 1 Mbps serial connection• Standard UART interface• SiliconWave and Ericsson modules tested

• Flexible application-level interface• Simple (virtual) serial port• TCP/IP via PPP• Custom protocols possible

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Hardware Details: DSPs• Daughtercard adheres to TI spec• Compatible with C62x, C67x & C64x boards

• Possible future use with C5x systems• Minimal resource requirements• Uses just one external interrupt• All transfers via external memory interface• Allows additional daughtercards to be used

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Software Tools• DSP software• Development in TI Code Composer• Compatible with CC 1.2x and 2.x• Only requires DSK tools

• Uses dsplib and imglib• No third-party libraries or extensions required

• Etrax software• Standard Linux development in C/C++• GNU tools (gcc, gdb, etc.)

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Image Capture Dataflow• Each pixel read is read from the camera• Daughtercard buffers one line• EDMA interrupted for each line• Buffer emptied by EDMA burst read• EDMA buffers full frame• DSP interrupted for full frame• Frame used only if DSP is ready

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Transmission Dataflow• DSP writes coded data to memory• EDMA constantly writes to EMIF• Etrax on daughtercard reads data• Data packaged and transmitted

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Testbed Software• Generic framework for dataflow• EDMA setup optimized for input & output

• Two coding schemes implemented• MPEG-4

• Advanced video compression• Designed for low-datarate applications

• JPEG2000• Advanced still image compression• Extremely good compression vs. quality

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MPEG-4 Encoder• Structure based on open source x86 code• Heavily optimized for C6x processors• Extensive use of TI assembly routines

• Implements MPEG-4 Simple Profile• Only one previous frame required

• Operates on 8 x 8 macroblocks• Minimizes internal data memory requirements

• Core uses 57 KB of program memory

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MPEG-4 Encoder Performance

• Depends heavily on cache configuration

L2 Cache Size 0KB 16KB 32KB 48KB 64KB

SRAM Size 64KB

48KB 32KB 16KB 0KB

Cache Associativity - 1-way

2-way

3-way

4-way

Frames/second 11.9 14.5 17.6 18.5 19.2

Encoder Performance on C6711

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JPEG2000 Image Compression

• New version of popular JPEG standard• Continuous tone still image compression• Wavelet based algorithm• More computational intensive than JPEG’s DCT• Much better compression ratios

• Useful features• Lossless and lossy options• Random access - no inter-frame dependence• Good control over quality vs. compression ratio

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JPEG2000 Encoder

• Based on JasPer codec• Open source reference implementation• Project of Image Power & U of British Columbia

• Very modular and abstracted design• Easy addition of features and formats• Great for PC execution• Bad for embedded DSP execution

• DSP optimizations• Reduce function calls in core code• Eliminate some extraneous format flexibilities

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JPEG2000 Encoder Results

• Operation on 32 x 32 pixel tiles• Constrained by DSP’s internal data memory

• Total code size around 300KB• More internal program memory boosts performance

CIF QCIF

C6711 0.17 0.46

C6416 6.2 16.5

Encoder Performance (frames/sec)

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Future Work: Hardware

• Interface to new C55x DSP systems• Dependent on availability from TI

• Further integrate components• Design single board system• Migrate wireless processing to DSP

• TI’s OMAP platform is good candidate

• Support full-duplex operation• Add audio support• Integrate video display

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Future Work: Software

• Implement MPEG-4 decoder• Relatively easy compared to encoder

• Further optimize JPEG2000 encoder• Reduce number of data structures• Minimize function calls• Migrate core to optimized assembly routines

• Increase tile size to reduce DMA transfers• Investigate better error protection• Supplement or replace Bluetooth error control

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Conclusions

• Modular & standards-based testbed• Realistic platform• Resembles capabilities of future mobile devices

• It works!• Hardware manufactured and tested• Software framework validated• Two compression standards implemented• Ready for future research

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Questions

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