Developing a multi-thread product -- Introduction

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Developing a multi-thread product -- Introduction

• M. Smith
• Electrical Engineering, University of Calgary
• Smithmr _at_ ucalgary.ca

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References

1. Understanding GPS Principles and Applications,
   1996, Elliott D. Kaplan
2. Digital Signal Processing A Practical Approach,
   1993, Emmanuel C. Ifeachor, Barrie W. Jervis
3. ADSP-TS101 TigerSHARC and Blackfin Processor
   Programming References, Analog Devices
4. Articles submitted to Circuit Cellar magazine by
   M. Smith, March 2004

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Introduction

• GPS traditionally done with ASIC/Processor
  combination
• Looking at FPGA/DSP combination for low end GPS
  receivers
• Technological interest in software radio
• Cheaper, quicker development cycle.
• Customizations for special applications
• From a talk by Darrell Anklovitch for ENEL619.23

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What is GPS?
Global Positioning System
24 satellite (SV) constellation
Orbiting 20,000 km from the surface of the Earth
in 12 hour cycles
Orbits are set-up to give global coverage 24
hours a day
Need at least 4 satellites in view to calculate a
position
(1)
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GPS Positioning Concepts
(1)

• For now make 2 assumptions
• We know the distance to each satellite
• We know where each satellite is
• Require 3 satellites for a 3-D position in this
  ideal scenario
• Requires 4 satellites to account for local
  receiver clock drift.

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GPS Signal Structure

• Each satellite transmits 2 carrier frequencies
  referred to as L1 (1575 MHz) and L2 (1227 MHz)
• Each carrier frequency is BPSK modulated with a
  unique PRN (pseudo random number) code
• The PRN code on L1 is called CA code (coarse
  acquisition), The PRN code on L2 is called P code
  (precise)
• CA code takes 1 ms for full PRN transmission at
  1MHz chip (bit) rate. P code takes 1.5 s for full
  PRN transmission at 10MHz chip rate
• Also modulated on each carrier is 50 Hz data that
  includes the current position of the satellite

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Determining Time
(1)

• Use the PRN code to determine time
• Use time to determine distance to the satellite
  distance speed of light time

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Algorithms to Find PRN Phase

• Time-domain Cross correlation 1/N ? x1 (n)
  x2(n)
• Coding equivalent to FIR filter, but need to
  filter N sets of data, each shifted by one data
  point looks like a final exam question to me.
• Correlation of perfectly matching signals gives a
  maximum value
• Correlation of 2 random data sequences tends to 0
• PRN code from different satellites are designed
  to correlate to 0.
• Frequency domain correlation 1/N F-1X1(k)X2(k)
  where F-1 is the inverse Discrete Fourier
  Transform and the Xs are the Discrete Fourier
  Transforms of two sequences

D
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Timing

• Frequency Domain 1/N F-1X1(k)X2(k)
• 1024 point FFT (2 NLOG2N)
• 1024 MULTS (N)
• 1024 point INV FFT (NLOG2N)
• Time Domain 1/N ? x1 (n) x2(n)
• 
  
  n 0
• 1024 MACs (N)
• 1024 Phases (N)

30,000 Complex operations
N-1
1,048,576 operations
(N2)
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TigerSHARC -- TS101 and TS201
TS101
TS201
Low-cost version 45 / chip Evaluation boards
950 eacheducational price
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Implementing a multi-thread systemworking on
batch data
Collect N pts _at_44 kHz ? array1 Collect N pts _at_44 kHz ? array2 Collect N pts _at_44 kHz ? array3 Collect N pts _at_44 kHz ? array1 Collect N pts _at_44 kHz ? array2 Process array1 Process array2 Process array3 Process array4 Transmit N pts _at_44 kHz ? array1 Transmit N pts _at_44 kHz ? array2 Transmit N pts _at_44 kHz ? array3
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Implementing a multi-thread system-- Laboratory
5 concepts
Collect N pts _at_44 kHz ? array1 Collect N pts _at_44 kHz ? array2 Collect N pts _at_44 kHz ? array3 Collect N pts _at_44 kHz ? array1 Collect N pts _at_44 kHz ? array2 Move array1 ? array4SimulateComplex Move array2 ? array5SimulateComplex Move array3 ? array6SimulateComplex Move array1 ? array4SimulateComplex Transmit N pts _at_44 kHz ? array4 Transmit N pts _at_44 kHz ? array5 Transmit N pts _at_44 kHz ? array6
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Essentially

• Take an audio Talk-through program
• for loop
• Read_a_sample Perform operation
  Write_a_sample
• Turn into 5-threads running under interrupts
• Idle thread
• Initialization thread sets up system, when
  ready launches the other threads then
  activates the first thread
• ReadValueThread,
• ProcessValueThread with simulated Complex
  Algorithm
• WriteValueThread

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Initialization Thread Lab. 5 early
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Main Threads example Lab. 5 early
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Need to investigate and understand system
behaviour and limitations
Concept of task priority
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Lab. 5 using real-time audio-test
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VDK Status History
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Laboratory 5 Done in C and C

• Stage 1 30
• Develop and investigate a multi-tasking system
  where the threads are free-running. Thread tasks
  are Sleep(time_task)
• Develop and investigate a multi-tasking system
  where the threads communicate through semaphores
  to control order of operation
• Stage 2 55
• Demonstrate and investigate turning an audio
  talk-through program into a multi-threaded
  system one point processed per interrupt
• Stage 3 15
• Demonstrate a batch processing system as a
  multi-threaded system
• Options
• Use SHARC ADSP-21061 boards (40 MHz) existing
  audio-libraries have not attempted
• Use Blackfin ADSP-BF533 boards (600 MHz)
  existing audio-libraries have been successful
  at home, but not here
• Use Blackfin ADSP-BF533 boards (600 MHz) using
  very simple, no frills, audio-talk though library
  surprising simple with 1 to 32 points being
  processed. Fails with 33 points. Code logic
  issue, not a timing issue as I can waste 25000
  cycles per block at 32 points

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Where to start?
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Adding the Initialization thread
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Making the InitializationThread a Boot Thread
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Add the thread programming control
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Avoid the free-running code
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Then add semaphores to control flow
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Tackled today

• GPS basic concepts
• Algorithm can be implemented in either
  time-domain or frequency domain
• Big time advantages in frequency domain for the
  GPS algorithm (unless add special instructions)
• Need to batch data for input, output and
  processing
• VDK is an Analog Devices VisualDSPTool for
  automatically generating the code for a
  multi-threaded system
• Laboratory 5 First part 30
• Implement a simple multi-threaded system where
  the threads mainly sleep, and either free run, or
  communicate through semaphores to control program
  flow