A DSP-Based Platform for
Wireless Video Compression
Patrick Murphy, Vinay Bharadwaj,
Erik Welsh & J. Patrick Frantz
Rice University
November 18, 2002
Motivations & Requirements
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Wireless video communication
Demand expected to explode
• Much more challenging than voice
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Standards not yet established
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Need modular hardware & software
Testbed should approximate real system
Similar hardware
• Portable code
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Testbed Description
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Source coding on Texas Instruments DSP
Similar to processors in most wireless devices
• Mature software development environment
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Bluetooth wireless interface
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Datarate comparable to future mobile systems
Decoding performed on separate PC
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Testbed Hardware
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Custom hardware
Inspired by TI Imaging Developers Kit
• Support for lower resolution imaging
• Integrates wireless interface & host processor
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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
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Axis Etrax 100LX
32-bit 100 MIPS RISC processor
• Runs full Linux operating system
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Uses 2.4.x kernels and glibc
Open source Bluetooth stack
Originally developed by Axis
• Now available under GPL
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Multichip Module
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Integrated flash, SDRAM and Ethernet interface
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Hardware Details: Camera
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Omnivision CMOS imager
16-bit digital interface
• Supports YUV 4:2:2 and raw RGB
• On-board image preprocessor
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Color space conversion
• White balance
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Configuration by I2C
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Easily controlled by Etrax processor
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Hardware Details: Bluetooth
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Support for variety of Bluetooth hardware
Up to 1 Mbps serial connection
• Standard UART interface
• SiliconWave and Ericsson modules tested
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Flexible application-level interface
Simple (virtual) serial port
• TCP/IP via PPP
• Custom protocols possible
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Hardware Details: DSPs
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Daughtercard adheres to TI spec
Compatible with C62x, C67x & C64x boards
• Possible future use with C5x systems
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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
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DSP software
Development in TI Code Composer
• Compatible with CC 1.2x and 2.x
• Only requires DSK tools
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Uses dsplib and imglib
• No third-party libraries or extensions required
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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
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Generic framework for dataflow
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EDMA setup optimized for input & output
Two coding schemes implemented
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MPEG-4
Advanced video compression
• Designed for low-datarate applications
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JPEG2000
Advanced still image compression
• Extremely good compression vs. quality
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MPEG-4 Encoder
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Structure based on open source x86 code
Heavily optimized for C6x processors
• Extensive use of TI assembly routines
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Implements MPEG-4 Simple Profile
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Operates on 8 x 8 macroblocks
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Only one previous frame required
Minimizes internal data memory requirements
Core uses 57 KB of program memory
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MPEG-4 Encoder Performance
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Depends heavily on cache configuration
Encoder Performance on C6711
L2 Cache Size
0KB
16KB
32KB
48KB
64KB
SRAM Size
64KB
48KB
32KB
16KB
0KB
Cache Associativity
Frames/second
11.9
1-way 2-way 3-way 4-way
14.5
17.6
18.5
19.2
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JPEG2000 Image Compression
New version of popular JPEG standard
• Continuous tone still image compression
• Wavelet based algorithm
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More computational intensive than JPEG’s DCT
• Much better compression ratios
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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
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Based on JasPer codec
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Very modular and abstracted design
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Open source reference implementation
Project of Image Power & U of British Columbia
Easy addition of features and formats
Great for PC execution
Bad for embedded DSP execution
DSP optimizations
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Reduce function calls in core code
Eliminate some extraneous format flexibilities
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JPEG2000 Encoder Results
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Operation on 32 x 32 pixel tiles
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Constrained by DSP’s internal data memory
Total code size around 300KB
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More internal program memory boosts performance
Encoder Performance (frames/sec)
CIF
QCIF
C6711
0.17
0.46
C6416
6.2
16.5
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Future Work: Hardware
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Interface to new C55x DSP systems
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Dependent on availability from TI
Further integrate components
Design single board system
• Migrate wireless processing to DSP
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TI’s OMAP platform is good candidate
Support full-duplex operation
Add audio support
• Integrate video display
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Future Work: Software
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Implement MPEG-4 decoder
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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
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Investigate better error protection
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Supplement or replace Bluetooth error control
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Conclusions
Modular & standards-based testbed
• Realistic platform
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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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