1. Ultra sound solution Profiles and other optimizations

2. Research Team discussion -- RECAP Ultra-sound probe (20 MHz) that sends out signals into body that reflect off moving blood cells in (Artery? Vein?) Ultra-sound frequency received is Doppler shifted compared to transmitted frequency Same as sound when ambulance goes by. Higher if approaching, lower if receding They get the positive frequencies (towards) on the left audio channel and negative frequencies (away) on the right audio channel. 11/10/2015.ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 2 / 33

3. Picture looks like this -- RECAP Note that the display loses all direction information Can I help them to output the maximum frequency? 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 3 / 33

4. Progress to this stage -- RECAP Gather single input values into buffer as part of ISR When buffer ready, launch an TTCOS processing task that executes outside the ISR -- MUST COMPLETE in time N * deltaT where N is buffer size and deltaT is sample time Take values from a previously processed buffer and send to output inside ISR Explored a number of pragmas for optimizing C++ code and looked at impact of C code Only looked at simple copy program 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 4 / 33

5. Snap shot code execution -- RECAP 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 5 / 33 A/D DATA CAPTURE INSIDE ISR D/A DATA OPERATION INSIDE ISR DATA PROCESSING OUTSIDE ISR MAJOR PROBLEM -- NEED TO RETRIEVE FROM END AND BEGINNING DATA BLOCK Assignment 2 – FIR operations on BLOCKS is another example

6. Approaches – two common -- RECAP Store complex number (a + jb) data block in two sections Real part in dm memory space and imaginary part in pm memory space Where to store FIR coefficients to avoid data data conflicts? Store complex number data block in dm space in double size array float normalArray[LENGTH] float complexArray[2 *LENGTH] Perhaps store FIR coefficients in pm space 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 6 / 33

7. Proposed algorithm – based on STFT – Short term FT -- RECAP Gather N points of data to circular buffer Using last 2 N points, and do on both channels Convert 2N real points to 2N complex points Perform 2N point FFT (complex numbers) with windowing Calculate absolute value of FFT of 2N points Calculate area under frequency curve (area) Find index where X% of frequencies are below this frequency (max frequency) This one frequency value is used as the best estimate of the maximum frequency over the last N points (put same value into all N points of output) (STFT limitation) 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 7 / 33

8. Switch to Testing framework -- RECAP Don’t test with TTCOS and real audio signals Don’t know what expected values are Testing framework can’t work with TTCOS anyway – CHECK errors take 1/ 30 s to print = lost samples 1500 Check circular buffer operation for data storage Check circular buffer operation when convert 2N real points to 2N complex points (different buffer, not circular buffer operations) Check Absolute calculation (complex to real) Check area and frequency maximum calculations Check FFT. Turn on optimizer and ‘hope things work in real time’ Plan B – Find better FFT code, that compiler can more easily optimize (for loops) Plan C -- SHARC has FFT Accelerator and there is sample code available 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 8 / 33

9. Revised code -- Error message strange 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 9 / 33

10. Errors and Defects -- RECAP We all make mistakes – the key is when we find the mistake If we find the mistake AFTER we move away from this part of the problem – we call the mistake – ‘An error’. Errors can be made in coding or design or life. If we find the mistake AFTER we move away from this part of the problem – we call the mistake – ‘A defect’. Defects can be made in coding or design or life. Defects are more costly to correct that errors 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 10 / 33

11. Code for absolute of complex number 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 11 / 33

12. 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 12 / 33

13. FFT code – legacy code Typical problem with legacy code Written by somebody else – how good or bad? No tests available Can be very difficult to write tests Useful article and book www.objectmentor.com/resources/articles/ WorkingEffectivelyWithLegacyCode.pdf www.objectmentor.com/resources/articles/ WorkingEffectivelyWithLegacyCode.pdf Michael Feathers 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 13 / 33

14. Some obvious tests for FFT Take any signal signal = IFFT(FFT(signal)) and signal = FFT(IFFT(signal)) WARNING signal starts as a real value and ends up as a complex value of the form value + j (close but not equal to zero) 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 14 / 33

15. Obvious tests for FFT Based on linear algebra If input is size N and is all ones (DC) then FFT results should have spike at frequency 0 with a size of N If input is size N and signal is sin(2 * pi * f * t / N) then should have spike at frequency f with a size of N (actually two spikes one at f and the other at –f since sin = (exp(jwt) + exp(-jwt)) / 2j Compare to MathLab results 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 15 / 33

16. Need a new RealToComplex( ) Note – framework indicates memory leak 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 16 / 33 delete complexDCSignal at end of TEST

17. First set of FFT tests Common error S = IFFT( FFT(S) ) / N; Matlab does this automatically – we must do manually TIME PENALTY 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 17 / 33

18. Make sure you rerun tests For every 3 errors fixed, 1 introduced SUSPECT CODE 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 18 / 33

19. KNOWN DEFECT This should work with this new buffer and old buffer, but uses next buffer instead Difficult to spot, even after release, as all the buffers will be very similar so results will be “Almost right” – problem with medical device – especially if you are the patient 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 19 / 33

20. Switch on the optimizing compiler DOES NOT HELP Where’s the timing info gone? Have to go in and tell optimizing compiler to add debug info and do rebuild 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 20 / 33

21. Here is the only compiler warning If more info available could go to SIMD 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 21 / 33

22. 2 / 2 efficiency 100% If’s take 5 / 7 of time 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 22 / 33

23. Detail – out of order execution 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 23 / 33

24. Performance hog – function in loop Also software loop 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 24 / 33

25. 3 cycles every time if not true NOT PREDICTED 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 25 / 33

26. Compare code BEFORE AFTER – SMALLER LOOP, NOT JUMP 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 26 / 33

27. Efficiency of FFT code Don’t even want to look Software bit reversing -- 30% of time SHARC can for hardware bit reverse address Continually calculates sine and cosine coeffs Okay if FFT done once – otherwise get an algorithm that uses table lookup Those while loops 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 27 / 33

28. Next step Do we need to worry? Is real-time performance there Add tested code into TTCOS and do a quick test TTCOS will send out error message if not working fast enough Look at using profiler to find out where the code is the slowest 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 28 / 33

29. Add to TTCOS Ausio program 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 29 / 33

30. It links in Debug – will it run? 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 30 / 33

31. It runs TTCOS is not complaining “no room for new tasks We are processing 128 points at 41000 Hz So each task must finish in 128 / 41000 s Or around 1/ 500 s or 2 ms Or 2000 * 500 cycles at 500 MHz= 1,000,000 Every cycle can do many things Lets turn profiling on 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 31 / 33

32. Turn on statistical profile What is a profiler? What is a statistical profiler? 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 32 / 33

33. Profile information – TOTALLY IMPRESSED Actually works better than I expected (profiler and code) – If the code works DEBUG OPTIMIZED 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 33 / 33

34. Get line by line information 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 34 / 33

35. Project Need to add the amplitude modulating code Do some more testing Use audacity as a simple oscilloscope Fix the known defects Must use only ½ the FFT data and not all Using wrong ‘old buffer’ But I am impressed!! Project is essentially there in about 1 week elapsed time 11/10/2015 ENCM515 – Ultrasound Problem Copyright smithmr@ucalgary.ca 35 / 33

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