04/19/23 1

Developing a multi-thread Simulation of GPS systemYou’ll only need to add the threads – all functions (except correlation( )) providedM. Smith

Electrical Engineering, University of Calgary

Smithmr @ ucalgary.ca

04/19/23 2 / 33

Tackled today

Why bother with a GPS example of a multi-tasking DSP problem?

Prototype of working product Explanation of the provided functions

Tests are provided so you can test out your assembly code versions of the correlation functions.

Lab. 4 and Take home quiz 4 How are they interlinked?

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Why bother?

Learn the basics of programming DSP within real time operation system constraints Interesting Basic concepts to understand GPS functionality

Ability to easily visualize work load Basic C++ correlation (provided by me) (Lab. 4) FFT correlation (provided by Analog as part of C++ library

(THQ4) Assembly FIR algorithm modified for correlation (Lab. 4 using

Lab 3 code provided by you) Use of CLU XCORR instruction (THQ4 -- Hints from Analog,

myself and Trevor) Research side

Allows me to test out the E-TDD tool set in RTOS environment on embedded system, and gain personal familiarity with problems of doing so.

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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

Use the PRN code to determine time Use time to determine distance to the

satellite distance = speed of light * time

(1)

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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

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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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 ReceiveSatellite1 X = 10 ReceiveSatellite2 X = 20 ReceiveSatellite3 X = 30

Part 3 – Add semaphores to get satellite tasks running in proper time sequences

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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

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Lab. 4 – Adding payloads to the threads Thread set to receive signals from satellites

Simulation – Clear receiveBuffer. Add satelliteX’s PRN signal stream to receiveBuffer based on satellite location and speed. Functions and their tests provided

Thread set to analyze received signal Correlate information in receiveBuffer with satelliteX PRN

stream to see if signal from satellite is present or not. Analysis functions and their tests provided Correlation function tests provided

Thread set to report on satellite status ErrorX means that signal to satellite signal X was lost

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Final result – VDK Thread Picture

Satellite thread generates signal into receiveBuffer

Analysis thread – long execution time – each tick = 0.05 ms

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Satellite signal “received” into receiveBuffer

Clear Add Add Add Startbuffer Sat1 Sat2 Sat3 Analysis

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Analysis errors can occur

Errors occur – here one satellite is active but algorithm gets confused.

Length of PRN too smallChoice of PRN poor – rand( ) poor?

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Satellite moving in and out of range

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InitializationThread::Run()InitializationThread::Run() {

VDK::CreateThread(kReceiverControlThread);VDK::CreateThread(kAnalysisThread);VDK::CreateThread(kError1);VDK::CreateThread(kError2);VDK::CreateThread(kError3);VDK::CreateThread(kReportThread);VDK::CreateThread(kReceiverBufferClear);VDK::CreateThread(kReceive1Satellite);VDK::CreateThread(kReceive2Satellite);VDK::CreateThread(kReceive3Satellite);

while (1) {VDK::PostSemaphore(kCaptureSignalSTART);VDK::Sleep(1500);if (VDK::GetUptime( ) > 20000) exit(0);

}}

You cancut-and-pastethis code from the slidePROVIDEDyour thread namesare the same as mine

Order of creationchanges the waythings look inVDK HISTORYwindow

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void ReceiverControlThread::Run()// You’ll need to add #include “Satellite.h”// Generate a PRN sequence Warning -- big problems with the rand( ) generator

const int prn_length = TEST_PRN_LENGTH;InitializeSatelliteData(prn_length);SetSatelliteVelocity(2, 60);SetSatelliteLocation(2, 0);

while (1) {VDK::PendSemaphore(kCaptureSignalSTART, 0);VDK::PostSemaphore(kReceiverBufferClearSTART);VDK::PendSemaphore(kReceiverBufferClearDONE, 0);VDK::PostSemaphore(kReceiver1SatelliteSTART);VDK::PendSemaphore(kReceiver1SatelliteDONE, 0);VDK::PostSemaphore(kReceiver2SatelliteSTART);VDK::PendSemaphore(kReceiver2SatelliteDONE, 0);VDK::PostSemaphore(kReceiver3SatelliteSTART);VDK::PendSemaphore(kReceiver3SatelliteDONE, 0);VDK::PostSemaphore(kAnalysisSTART);VDK::PendSemaphore(kAnalysisDONE, 0);VDK::PostSemaphore(kCaptureSignalDONE);

}

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ReceiverBufferClear::Run()#include "Satellite.h"// ReceiverBufferClear Run Function (ReceiverBufferClear's main{}) voidReceiverBufferClear::Run(){while (1) { // TODO - Put the thread's "main" body HERE

VDK::PendSemaphore(kReceiverBufferClearSTART, 0);ClearReceiveBuffer( );VDK::PostSemaphore(kReceiverBufferClearDONE);

// Use a "break" instruction to exit the "while (1)" loop }

// TODO - Put the thread's exit from "main" HERE // A thread is automatically Destroyed when it exits its run function}

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Adding satellite datavoid Receive2Satellite::Run() { // Data not added from this satellite while (1) {

VDK::PendSemaphore(kReceiver2SatelliteSTART, 0);// TransferSatelliteDataToReceiveBuffer(1);VDK::PostSemaphore(kReceiver2SatelliteDONE);

}}

void Receive3Satellite::Run() { // Data added while (1) {

VDK::PendSemaphore(kReceiver3SatelliteSTART, 0);TransferSatelliteDataToReceiveBuffer(2);VDK::PostSemaphore(kReceiver3SatelliteDONE);

}}

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AnalysisThread::Run()voidAnalysisThread::Run() {

bool valid_results; while (1) { // TODO - Put the thread's "main" body HERE

VDK::PendSemaphore(kAnalysisSTART, 0);AnalyseReceiveBuffer( );valid_results = ValidateResults( );if (!valid_results) {

VDK::PostSemaphore(kReportSTART);VDK::PendSemaphore(kReportDONE, 0);

}VDK::PostSemaphore(kAnalysisDONE);

}}

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void ReportThread::Run( )void ReportThread::Run() { while (1) {

VDK::PendSemaphore(kReportSTART, 0);if ((satelliteActive[0] != MYsatelliteActive[0]) || (satelliteLocation[0] != MYsatelliteLocation[0]))

VDK::PostSemaphore(kSatellite0LOST);if ((satelliteActive[1] != MYsatelliteActive[1])

|| (satelliteLocation[1] != MYsatelliteLocation[1]))VDK::PostSemaphore(kSatellite0LOST);

if ((satelliteActive[2] != MYsatelliteActive[2])|| (satelliteLocation[2] != MYsatelliteLocation[2]))

VDK::PostSemaphore(kSatellite0LOST);VDK::PostSemaphore(kSatellite1LOST);VDK::PostSemaphore(kSatellite2LOST);VDK::PostSemaphore(kReportDONE);

}}

Just spotted a BUG

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What you’ll need to modify

void CorrelateAlongReceiverBuffer(int *satellitePRN, int array_size, int *correlation_result){

for (int i = 0; i < RECEIVE_BUFFER_LENGTH; i++)correlation_result[i] = 0;

for (int result_index = 0; result_index < RECEIVE_BUFFER_LENGTH - array_size; result_index++) {

int sum = 0;

for (int sum_index = 0; sum_index < array_size; sum_index++) sum = sum + satellitePRN[sum_index] *

receiveBuffer[sum_index + result_index];correlation_result[result_index] = sum;

}}

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Provided “Satellite.h”#ifdef DECLARE_SATELLITE_VARIABLES

#define EXTERN#else

#define EXTERN extern#endif

#define RECEIVE_BUFFER_LENGTH 256EXTERN int receiveBuffer[RECEIVE_BUFFER_LENGTH];void ClearReceiveBuffer(void);

#define NUM_SATELLITES 3#define MAX_PRN_LENGTH 128#define TEST_PRN_LENGTH 128

// Generate a pseudo-random number sequence // Warning -- big problems with the rand( ) generator// when generating random bits -- (rand ( ) >> X ) % 2

#define SATELLITE_SEED 0x12397

EXTERN pm int satellitePRN[NUM_SATELLITES][MAX_PRN_LENGTH];

EXTERN pm bool satelliteActive[NUM_SATELLITES];EXTERN pm int satelliteLocation[NUM_SATELLITES];EXTERN pm int satelliteNextLocation[NUM_SATELLITES];EXTERN pm int satelliteVelocity[NUM_SATELLITES];

EXTERN pm int MYsatelliteLocation[NUM_SATELLITES];EXTERN pm bool MYsatelliteActive[NUM_SATELLITES];EXTERN pm int MYsatelliteNextLocation[NUM_SATELLITES];EXTERN pm int MYsatelliteVelocity[NUM_SATELLITES];

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Provided “Satellite.h”void TransferSatelliteDataToReceiveBuffer(int which_satellite);bool InitializeSatelliteData(int prn_length);void SetSatelliteVelocity(int which_satellite, int which_speed);void SetSatelliteLocation(int which_satellite, int which_distance);int GetSatelliteVelocity(int which_satellite);int GetSatelliteLocation(int which_satellite);bool InitializeMYSatelliteData(void);void SetMYSatelliteVelocity(int which_satellite, int which_speed);void SetMYSatelliteLocation(int which_satellite, int which_distance);int GetMYSatelliteVelocity(int which_satellite);int GetMYSatelliteLocation(int which_satellite);void CrossCorrelate(int *first, int *second, int *correlation_result, int array_size);void CorrelateAlongReceiverBuffer(int *satellitePRN, int array_size, int

*correlation_result);int MaximumLocation(int *correlation_result, int array_size);int MaximumValue(int *correlation_result, int array_size);

bool ValidateResults(void);void AnalyseReceiveBuffer(void);

int CalculateCorrelationRange(void);int CalculateCorrelationAverage(void)

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Provided Tests ExamplesTEST(CrossCorrelationTest, DEVELOPER_TEST) {

TEST_LEVEL(9);

int first[ARRAY_SIZE] = {1, 0, 0, 0, 0, 0, 0, 0};int second[ARRAY_SIZE] = {0, 1, 0, 0, 0, 0, 0, 0};int third[ARRAY_SIZE] = {0, 0, 1, 0, 0, 0, 0, 0};int correlation_result[ARRAY_SIZE];int maximum_location;

CrossCorrelate(first, first, correlation_result, ARRAY_SIZE);maximum_location = MaximumLocation(correlation_result, ARRAY_SIZE);CHECK_EQUAL(maximum_location, 0);

CrossCorrelate(first, second, correlation_result, ARRAY_SIZE);maximum_location = MaximumLocation(correlation_result, ARRAY_SIZE);CHECK_EQUAL(maximum_location, 1);

etc. ……..}

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Tackled today

Why bother with a GPS example of a multi-tasking DSP problem?

Prototype of working product Explanation of the provided functions

Tests are provided so you can test out your assembly code versions of the correlation functions.

Lab. 4 and Take home quiz 4 How are they interlinked?