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Averaging FilterBasic SHARC assembly

and adding automated tests

Example of project development on SHARC using C++ and assembly

Planned for Tutorial Thursday 2nd October

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Concept “Single Point Copy” Audio Filter

• Co-operative operating system used– SHARC uTTCOS guarantees that only one task will run at a time – Means, tasks ARE NOT swapped out but run-in-turn with the

exception of ONE pre-emptive task (which interrupts other tasks) • You can automatically generate files for a uTTCOS project in

ENCM515/Assign1 directory using uTTCOS_Helper plug-in– Hidden hardware capture of audio signal causes an interrupt that

places audio values in a known location• You must add a pre-emptive task to process the audio signal

to the uTTCOS to-do list of tasks– Pre-emptive tasks must have fast ‘in-and-out fast’ characteristics –

absolute minimum time spend in pre-emptive task. Must be guaranteed to finish with 50% of 1 system TIC

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Add Pre-emptive task to uTTCOS to-do list. Use to test audio equipment in lab.

Use of include path operation means only 1 header files across 3 projects

Project shouldcompile withCopy_Left( ) stub

• The code will not run in the lab because of a logical defect)

• What’s the defect?

4

RECAP --Learn optimization via basic DSP algorithm“Average last N points” (trivial LP filter)

Requirements– Output signal of filter y[n] is

average of last N input values x[n-j], 0 <= j < N – y[n] = ( (x[n] + x[n-1] ……..x[n – (N-1)]) ) / N

Need to store (and update) last N audio values captured– Need to store in first-in first-out (FIFO) buffer

Problem -- audio start up transient– How do you handle the first “N” values?

• Assume that x[-1], x[-2] …. X[n – (N-1)] = 0.• Basically means you pre-fill the FIFO buffer with zeros• y[0] = ( x[0] + 0 + 0 + 0 ) / N;

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RECAP -- Code Design

• Discard oldest value in FIFO (oldest was first in, so first out

• This provides room to add new value to FIFO buffer• Output calculated by averaging all values in FIFO

• Note N will be set as small number (e.g. N = 16) during some parts of test, and set large when timing done.– Don’t hand in labs handed in with poor timing test (D)

• Use no magic numbers use in code– No loops involving for (j = 0; j < 1024; j++)– Use (j = 0; j < N; j++) where N is declared in Assign1.h so a

single N is used across project including C, C++ and ASM

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Develop a personal software processto minimize mistakes and wasted time

• Do a code review for syntax errors– Make a list of errors so that you can identify YOUR most common

mistakes AND STOP making them – One less repeated error per laboratory minimum

• The number of syntax errors the compiler finds after your code review is related to the number of logical (unfound) defects in your code.

• The number of syntax errors the compiler finds after your code review is related to the amount of time you will waste debugging your code looking for those hidden defects you did not find.

• Watts Humphreys PSP – If spend 30 minutes coding then spend 25% of 30 minutes on review

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RECAP -- Understanding C properly is a key to real-time programming

• What does this code mean? -- Keyword ‘static’

• It means– When loading the program and data into the processor’s data and

program memory using the embedded system BOOT sequence, make permanent private space ‘in general memory’ for an array FIFO[ ].

– As part of the embedded system BOOT sequence set all the values to zero before starting the program• NOTE: This setting to zeroes is NOT a run-time operation• NOTE: If restart the program (rather than reloading it), then ZEROS are not

stored in FIFO[ ] – unknown E.B. values are stored there.

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RECAP Try out averaging code

• Build Assign1Library project , then CLEAN and build Assign1 project to force it to use new library (Eclipse bug)

• Averaging removes high frequencies.

• Old vinyl records (1920) lacked high frequency components

• Assignment 1 : – What value of N to make 2011 music sound like 1920?– What does this sort of averaging do, and why?

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Build Library – Clean and Build project-- Expect a linker error to be reported as no new code is present

• Check that error message is what you expect

Missing function is NAME-MANGLED meaning thanLinker is looking for C++ code and not assembly code.Typically means that “header file is wrong”ASK ME WHAT IS WRONG WITH HEADER FILEAND THEN NOTE IN IN YOUR NOTES

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Understanding the code we use

• This processor has two kinds of memory– dm – data memory– pm – program memory

• HARVARD architecture of processor– Ability to access data memory and program memory at

the same time. – Major speed improvement over von Neumann

architecture

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Accesses can be made directly to a specific memory address

• Just because you can access memory this way, does not mean that this is the fastest code

?? #define _LeftChannel_In1 0x40???? // Used “extern” on last slide so define issue is solved automatically by the linker

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Assembler message with adjustmentOutput volume is zero – WHY???

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Output volume is zero after we do the multiply

• Need to switch to a testing environment to work out why.– Actually, we can make a guess.

• We are doing ‘integer mathematics’ (a.k.a. Blackfin)• Blackfin and MIPS

– 300 cycles for FADD via special floating point subroutines

• SHARC is ‘floating point ‘ processor– 1 cycle for FADD via special floating point instructions

• In future, we will set up tests first so that we know what the answer will be from complex algorithms.

F2 = F2 * F5 (float multiplication)R2 = R2 * R5 (two types of integer)

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Avoid this refactoring defectNote CCES warns you (some what)

But unless you read the warning then it does not help

Mistake you made

Assembler trying to warn you thatyou are using an“integer” op ratherthan a floating point operation

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Assembler is ‘lying’ (Disassembly window)Only 1 in 5 is ‘real float’ instruction

• Memory stores are bit patterns – not floats or integers

• Constants are bit patterns -- not integers or floats

NO NEED TO USESILICON FORUNNECESARY FLOAT INSTRUCTIONSWHEN EXISTING INTEGERWORK “PERFECTLY WELL”

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XP-Inspired Life cycle for real-time DSP (see Smith et al articles on 515 web-site)

• Design – wish-list of ‘stories’ to implement• Write Tests to show how code should work• Write C++ code to satisfy tests (Get to work)• Generate resource chart based on processor architecture to

calculate best ‘theoretical’ speed– If ‘theoretical speed’ meets your ‘real-time requirements’ you, then

worth while trying to optimize!. – If ‘theoretical speed’ does not work for you then ‘find a different

algorithm’, optimization is not going to help.• Use already written tests to prove that (highly optimized)

assembly code WORKS as well as being fast• NOTE: Theory calculation etc. is done WITHOUT writing any

assembly code. Timing calculation is all about “thinking” about what is needed and about actually not doing it. Assembly coding comes when it is needed and not before

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Lets try the approach with CopySingle( )OFF-LINE testing – without uTTCOS, with faked audio signals

• Assign1_Tests – convert to E-Unit using Open-CCES-ame Plug-in

• First test will be for ‘CopySingleCPP’• Change include path for .h to include Assign1_Library and add

(debug version) Assign1_Library.dlb

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Inside ‘Assign1_Test’ projectThere are .h and .dlb links into Library

Make LINKS to Assign1 Library.dlb and .h header filesin directory and NOT copies of files and librariesDone by adding library path and include path information

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Modify tests to validate C++ and assembly copy routines

• Confusing – Cntrl-SPACE completion macro knew about LeftCPP( ) etc – but look at all error warnings

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Did a project clean and then build

Do code review to find final error

This was arefactoring

errorwhen I changed file

namesChange CONTROL

and NOTIFY macros to include CPP(See next slide)

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Big errors on Build and Link

• WE ARE TESTING OFF_LINE -- We are no longer running with a real audio interface (All variables defined in uTTCOS_Library used in Assign1 project)

• Actually good – Since we don’t know the actual audio values coming in when running in real-time, then we can’t test to see if we are processing them correctly

• Solution – Build a mock audio device and add the code to the project.

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Here is the Mock Audio DeviceAsk me how do I fix the error?

• Is my coding mistake an “error” or a “defect”?• Did I do a code review before compiling?

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Run the tests -- Missing Open-CCES-ame feature Click and go to Error. For nowRight click on blue bar to show line numbers

CLICK ON ERROR TO GO TO FAILING TEST – NOT YET POSSIBLE IN CCES. (If somebody is good at Java – I will tell them what is needed and we can discuss a price)

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CLICK ON ERROR TO GO TO FAILING TEST – NOT YET POSSIBLE IN CCES

• If somebody is good at Java – I will tell them what is needed and we can discuss a price.– We could double the money by jointly writing a CC article on this. – Published articles look good on CVs and scholarship application– They are not “articles” but “technical transfer papers” on your CV– Also possible to do during 4th year projects

• We have example code running in C++ and C# for an earlier IDDE• In principle I could do this (if I had the time)

– Find and capture the console window – Parse through console window and rewrite error messages in colour

• This is out of my “Java” comfort zone– Make the error clickable so that we can make the editor jump to that

location

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Straight forward to addmore tests to see if there is a pattern in the defect result

Why is there a code defect and not a code error?

Depending on your definition s -- Why is there a design defect and not a code error?

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Is there a pattern in the error messages?If exists, then hints at defect to solve

• Output value is wrong, but the wrongness scales with the input value size (NGTTY- HLTTMTWO)

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Use Open-CESS-ame to add new test group for Averaging code – 3 styles of tests

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Time test – measure in us Must be less than 20 us per point (1 audio channel)

Un-automated testing,

But we need to collect details And don`t have to do much analysis in Lab

Only doing 5 labs – not yet worth automating?

Timing MUST be done with long filtersWhat is filter length here

NEW REQUIREMENTAdd the size of the averaging filter as part of the printfstatement

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Interesting CCES IDDE code ran at different speed than VDSP IDDE code

CCES has differentC++ device buffercharacteristicsapparently forprintf( )

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Let`s try optimizing the C++ code(Switching between debug and release development)

• Right click Assign1Library.cpp and make a copy as Assign1LibraryOptimized.cpp• Change function names e.g. AverageSingleAudioValue_LeftCPP to

AverageSingleAudioValue_LeftCPPOptimized – delete other functions in file• Add new function to include file• Right click on Assign1LibraryOptimized.cpp and select properties• Under C/C++ Build | Settings select General and then Enable OptimizationNote – we are just optimizing the C++ code in this file and not in the whole library

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Add new test for optimized codeModify EUNIT main to show only failures

Don’t understand why there is an editor indicated error.

Tried CLEANBig difference between optimized and unoptimized C++Question is the code still working now its optimized (Actually never tested before)

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New test – used tocompare to ‘theoretical’Analysis of cycles used in code

Remember – we are also • timing the time

around the loop • and the time to

jump in and out of routines

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Testing the code’s correctness should have been done before optimization

• Warning – if FIFO_SIZE is small when testing – then will pass timing tests but be useless in real life

Note – This test “assumes”that input signals is stayingconstants

Need a better test