Averaging Filter
Basic 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
•
•
The code will not
run in the lab
because of a logical
defect)
What’s the defect?
Project should
compile with
Copy_Left( )
3
stub
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 process
to 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 than
Linker is looking for C++ code and not assembly code.
Typically means that “header file is wrong”
ASK ME WHAT IS WRONG WITH HEADER FILE
AND 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 adjustment
Output 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
F2 = F2 * F5 (float multiplication)
R2 = R2 * R5 (two types of integer)
• In future, we will set up tests first so that we know
what the answer will be from complex algorithms.
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Avoid this refactoring defect
Note CCES warns you (some what)
But unless you read the warning then it does not help
Mistake you made
Assembler trying
to warn you that
you are using an
“integer” op rather
than a floating point
operation
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Assembler is ‘lying’ (Disassembly window)
Only 1 in 5 is ‘real float’ instruction
NO NEED TO USE
SILICON FOR
UNNECESARY
FLOAT INSTRUCTIONS
WHEN EXISTING INTEGER
WORK “PERFECTLY WELL”
• Memory stores are bit patterns – not floats or
integers
• Constants are bit patterns -- not integers or floats
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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 16
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’ project
There are .h and .dlb links into Library
Make LINKS to Assign1 Library.dlb and .h header files
in directory and NOT copies of files and libraries
Done by adding library path and include path information
18
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 a
refactoring
error
when I changed file
names
Change 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 Device
Ask 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 now
Right click on blue bar to show line numbers
CLICK ON ERROR TO GO TO FAILING TEST – NOT YET POSSIBLE IN CCES. (If somebody is
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good at Java – I will tell them what is needed and we can discuss a price)
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 add
more 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?
25
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)
Timing MUST be done with long fil
What is filter length here
NEW REQUIREMENT
Add the size of the averaging
filter as part of the printf
statement
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?
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Interesting CCES IDDE code ran at
different speed than VDSP IDDE code
CCES has different
C++ device buffer
characteristics
apparently for
printf( )
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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 Optimization
Note – 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 code
Modify EUNIT main to show only failures
Don’t
understand
why there is
an editor
indicated
error.
Tried CLEAN
Big difference between optimized and unoptimized C++
Question is the code still working
now its optimized (Actually never tested before) 31
New test – used to
compare 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
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routines
Testing the code’s correctness should
have been done before optimization
• Warning
– if
FIFO_SIZE
Note – This test “assumes” is small
that input signals is staying when
constants
testing –
then will
Need a better test
pass
timing
tests but
be
useless in
real life
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