1. Developing a multi-thread product -- Introduction
M. Smith
Electrical Engineering, University of Calgary
ucalgary.ca
12/4/2018

2. Tackled today GPS example of a multi-tasking DSP problem
What is GPS and how does it fit into Lab. 4?
Lab. 4 concepts
VisualDSP VDK environment – 1 hour prelab.
Adding a boot thread
Adding (and then creating) free-running threads
Adding Semaphore so threads communicate
12/4/2018

3. References
Understanding GPS Principles and Applications, 1996, Elliott D. Kaplan
Digital Signal Processing – A Practical Approach, 1993, Emmanuel C. Ifeachor, Barrie W. Jervis
ADSP-TS101 TigerSHARC and Blackfin Processor Programming References, Analog Devices
Articles submitted to Circuit Cellar magazine by M. Smith, March 2004
12/4/2018

4. 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
12/4/2018

5. 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)
12/4/2018

6. 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.
12/4/2018

7. 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
12/4/2018

8. Determining Time Use the PRN code to determine 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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9. 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
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-1[X1(k)X2(k)] where F-1 is the inverse Discrete Fourier Transform and the X’s are the Discrete Fourier Transforms of two sequences D
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10. Timing Frequency Domain 1/N F-1[X1(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)
12/4/2018

11. TigerSHARC -- TS101 and TS201 TS101 TS201 Low-cost version $45 / chip
Evaluation boards $950 each educational price
12/4/2018

12. Lab. 4 and Take-Home Quiz 4
Demonstrate developing a multi-threaded environment involving the receiving and analysis of 3 satellite signals
Lab 4
VDK environment
Use of current assembly FIR code for correlation analysis
Take-home quiz (Done individually)
Use Analog Devices provided FFT code
Develop your own assembly language code using CLU functionality -- XCORRS
12/4/2018

13. Lab. 4 – Parts 1, 2 and 3 – done as pre-laboratory tasks – about 1 hour
Part 1 -- Create an Initialization Thread
Use VDK::Sleep(200) sleep as a work load
Part 2 – Launch (create) Satellite Receiver Tasks as free running tasks
Use VDK::Sleep(X) as a work load
ClearReceiverThread X = 100
ReceiveSatellite X = 10
ReceiveSatellite X = 20
ReceiveSatellite X = 30
Part 3 – Add semaphores to get satellite tasks running in proper time sequences
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14. Lab. 4 – Continued – details to be added
Part 4 -- Add Satellite Receiver Tasks Payloads
Download payload code from the web – code provided
Part 5 – Generate E-TTD tests for correlation function designed using your existing FIR filter code
Part 6 – Add analysis and reporting threads
Part 7 – adjust task priorities to make realistic and working
Demo and code hand-in with minor write-up
12/4/2018

15. Adding the initialization Thread
Blackfin code (VisualDSP 3.5) can be found at
TigerSHARC VDK
Different implementation for each version of processor (0.1 or 1.0) because of number of available timers on the chips
Slightly different setup between Visual DSP 3.5 and 4.0 because of the silicon differences mentioned above.
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16. VDK set-up for TigerSHARC (3.5)
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17. VDK Setup – Visual DSP 4.0
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18. Adding the Initialization Thread
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19. Making the InitializationThread a Boot-Thread
Automatically Generated Thread Code
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20. Adding a VDK::Sleep(200) work load to the Initialization Thread
VDK-Thread activity window can be activated through VIEW | VDK window menu option – you can Zoom into find fine details of certain activities WARNINGL If the silicon option are incorrect – only the IDLE thread seen
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21. Thread window legend (Right click in thread window to activate)
Running
Sleeping
Status change
Tick (0.05 ms default)
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22. Now add the following threads with following VDK::Sleep( ) periods
ReceiverControlThread ticks
ReceiverBufferClear ticks
Receive1Satellite ticks
Receive2Satellite ticks
Receive3Satellite ticks
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23. Thread code automatically generated Example after running the code
Problem – the threads have not been created – so they exist but don’t run
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24. Still problems All threads are launched
But one thread has taken over all the resources of the system
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25. Reason for Problem Thread is just spinning its wheels
Forgot to add the sleep?
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26. Solution Thread now all in existence – but free running
Need to add “semaphores” to gain control
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27. Receiver Requirements
On receipt of “Capture Signal” semaphore
Clear ReceiverBuffer
When receiver buffer is cleared
Grab satellite signals 1, 2 and 3
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28. Requirements rephrased ReceiverControlThread
VDK::PendSemaphore(kCaptureSignalSTART, 0);
On receipt of “Capture Signal” semaphore
VDK::PostSemaphore(kReceiverBufferClearSTART)
Clear ReceiverBuffer
VDK::PendSemaphore(kReceiverBufferClearDONE, 0);
When receiver buffer is cleared
VDK::PostSemaphore(kReceiver1SatelliteSTART);
VDK::PostSemaphore(kReceiver2SatelliteSTART);
VDK::PostSemaphore(kReceiver3SatelliteSTART);
Grab satellite signals 1, 2 and 3
VDK::Sleep (200)
VDK::PostSemaphore(kCaptureSignalDONE);
12/4/2018

29. Requirements rephrased
ReceiverBufferClear
VDK::PendSemaphore(ReceiverBufferClearSTART, 0);
VDK::Sleep (10); // Will be replaced by process later
VDK::PostSemaphore(ReceiverBufferClearDONE);
Typical Satellite Thread
VDK::PendSemaphore(ReceiverXSatelliteSTART, 0);
VDK::Sleep (X); // Will be replaced by process later
VDK::PostSemaphore(ReceiverXSatelliteDONE);
What are the syntax errors in the code?
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30. Adding a semaphore
12/4/2018

31. Method code added Why does not anything work?
What do you have to do to get this?
1 line change
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32. Some issues remaining
Blue bar means what? Why is distance between Init Thread
Green bar means what? and start of Receiver Control thread
Grey bar means what? changing? Yellow arrow means what? Is it a problem that Satellite 3 task finishes after receiver control thread starts to sleep?
12/4/2018

33. Tackled today GPS example of a multi-tasking DSP problem
What is GPS and how does it fit into Lab. 4?
Lab. 4 concepts
VisualDSP VDK environment – 1 hour prelab.
Adding a boot thread
Adding (and then creating) free-running threads
Adding Semaphore so threads communicate
12/4/2018