Single Value Processing Multi-Threaded Process

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Single Value Processing Multi-Threaded Process

• M. Smith,
• Electrical and Computer Engineering,
• University of Calgary,
• smithmr _at_ ucalgary.ca

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Timing

• Frequency Domain 1/N F-1X1(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)
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Implementing a multi-thread systemworking on
batch data
Collect N pts _at_44 kHz ? array1 Collect N pts _at_44 kHz ? array2 Collect N pts _at_44 kHz ? array3 Collect N pts _at_44 kHz ? array1 Collect N pts _at_44 kHz ? array2 Process array1 Process array2 Process array3 Process array4 Transmit N pts _at_44 kHz ? array1 Transmit N pts _at_44 kHz ? array2 Transmit N pts _at_44 kHz ? array3
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Implementing a multi-thread system-- Laboratory
5 concepts
Collect N pts _at_44 kHz ? array1 Collect N pts _at_44 kHz ? array2 Collect N pts _at_44 kHz ? array3 Collect N pts _at_44 kHz ? array1 Collect N pts _at_44 kHz ? array2 Move array1 ? array4SimulateComplex Move array2 ? array5SimulateComplex Move array3 ? array6SimulateComplex Move array1 ? array4SimulateComplex Transmit N pts _at_44 kHz ? array4 Transmit N pts _at_44 kHz ? array5 Transmit N pts _at_44 kHz ? array6
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Essentially

• Take an audio Talk-through program
• for loop
• Read_a_sample Perform operation
  Write_a_sample
• Turn into 5-threads running under interrupts
• Idle thread
• Initialization thread sets up system, when
  ready launches the other threads then
  activates the first thread
• ReadValueThread,
• ProcessValueThread with simulated Complex
  Algorithm
• WriteValueThread

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Essential, if not exact, concept of
multi-threading code

• Do all the initial preparation of the board
• Set up stack
• Set up C/C environment
• Set up processor timer
• Default on Blackfin ADSP-BF533 board every 0.05
  ms (called a TIC) an interrupt occurrs
• Start with an IDLE Thread
• When first TIC occurs the interrupt handler
  will cause the Scheduler ISR to run

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Scheduler ISR

• Save all the registers (etc) of the IDLE thread
  to the IDLE thread context buffer
• Recover all the registers for the scheduler ISR
  context buffer (saved somewhere during the
  initialization procedure)
• There had better be a boot thread otherwise
  system hangs
• VDK tool will not let you build a system without
  at least one boot thread
• Decide which boot thread has the highest
  priority?
• Save all the registers from the Scheduler ISR
  back into the context buffer
• Recover all the registers for the boot thread
  from its context buffer
• Return from ISR
• We have now performed a context switch between
  the IDLE thread and the BOOT thread.

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Boot thread

• The boot thread now executes until the first TIC
  occurs (next ISR call)
• We now switch back into Scheduler
• Save all the registers (etc) of the FIRST BOOT
  THREAD thread to the thread context buffer
• Recover all the registers for the scheduler ISR
  context buffer
• Other threads need launching?
• If there are other Boot threads then launch them
  depending on their priority and the ROUND ROBIN
  scheduling behaviour set by the programmer for
  tasks of equal priority
• If a boot thread has requested that other threads
  need launching then launch those. Unclear when
  the VDKCreateThread operation occurs

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The launching of threads
Looks like threads get launched during a TIC
meaning that anothercontext switch occurs for
each VDKCreateThread ( )
Does that apply to VDKPostSemaphores(
) too?
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Back in scheduler

• Other threads need launching?
• If there are other Boot threads then launch them
  depending on their priority and the ROUND ROBIN
  scheduling behaviour set by the programmer for
  tasks of equal priority
• If a boot thread has requested that other threads
  need launching then launch those.
• Have threads posted semaphores?
• Store them in a posted semaphore table.
• Threads can also post messages but I have not
  worked that out yet
• Are threads pending semaphores?
• Depending on which task is running now, and its
  relative priority to tasks that are pending
  semaphores then either perform context switching
  or not
• How do you handle conflicts? I think that is my
  problem with my final version of Lab. 5 part 3

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Laboratory 5 Done in C and C

• Stage 1 30
• Develop and investigate a multi-tasking system
  where the threads are free-running. Thread tasks
  are Sleep(time_task)
• Develop and investigate a multi-tasking system
  where the threads communicate through semaphores
  to control order of operation
• Stage 2 55
• Demonstrate and investigate turning an audio
  talk-through program into a multi-threaded
  system one point processed per interrupt
• Stage 3 15
• Demonstrate a batch processing system as a
  multi-threaded system
• Options
• Use SHARC ADSP-21061 boards (40 MHz) existing
  audio-libraries have not attempted
• Use Blackfin ADSP-BF533 boards (600 MHz)
  existing audio-libraries have been successful
  at home, but not here
• Use Blackfin ADSP-BF533 boards (600 MHz) using
  very simple, no frills, audio-talk though library
  surprising simple with 1 to 32 points being
  processed. Fails with 33 points. Code logic
  issue, not a timing issue as I can waste 25000
  cycles per block at 32 points

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Original audio-talk through program
ISR routineChannel to Channel Copy
Multi-tasking versionof ISR routine
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Step 1 Add Talk-through program to Lab. 5 A
multi threading example
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Step 2 Investigate Thread Behaviour
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Step 3 Fix Thread Behaviour
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Step 4 Start migrating code to the various
threads -- Fix ISR behaviour
ORIGINAL
NEW VERSION
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Fix Thread Behaviour

• Initialization thread
• Creates other threads andthen waits for ever
• ReadThread
• Moves my_In Value ? Process Value
• ProcessThread
• Moves Process Value ? ProcessDone Value
• Calls a non-optimizable to nothing routine
  SimulateMoreComplexProcess(cycles_to_waste)
• WriteThread
• Moves ProcessDone Value ? my_Out Value

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Final ReadThread
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Final ProcessThread
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Final WriteThread
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Thread Behaviour depends on Task priorities
ALL TASKS HAVE EQUAL PRIORITY
WRITE TASK HAS HIGHER
PRIORITY THAN PROCESS TASK1) Read Task sends
semaphore to Process Task2) Process Task sends
semaphore to Write Task and starts to waste
cycles3) Scheduler determines that Write Task
can start, send semaphore to Read Task, and
finish and then4) Scheduler lets Process Task
finish (? Why not let Read Task restart?)
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Thread Behaviour

• Useless as system is free running and the
  signals input and output have no relationship to
  samples generated by ISR
• Some samples repeated many times, others are not
• Number of repeats depends on the time that
  ProcessThread takes to execute

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Need to add an ISR semaphore
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Read Thread starts on ISR semaphore
STANDARD APPROACHVDKPostSemaphore( ) DOES
NOT WORK
Blackfin Assembly codelooks like 68K With LINK,
UNLINK, RTS instructions
MACRO
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Many issues still need handling

• How much time is available before losing sound
  quality?
• What are the best priorities for the tasks, and
  does that priority depend on how much time is
  spent in ProcessTask?
• What is the best setting for the task scheduler
  TIC time (based on processor internal timer)?
• Too fast too much time saving / recovering
  registers during task switching
• Too slow problems with interrupts being missed
  or values being over-writtem

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Scheduling based on TIC time
DEFAULT TIC 0.05 ms
TIC 0.005 ms Dont forget TICs are shortened
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Which is the Slower / Faster TIC time?
Question how does the thread status history
reflect sound quality?
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Tackled today

• Examined concepts of how multi-tasking is
  implemented
• Used
• Existing audio-talk though program and
• Lab. 5 multi-threading demonstration code
• Ended up with a multi-threading audio-talk
  through program that would give us an indication
  of how many cycles available when ProcessThread
  has increased complexity
• Final part of laboratory 5 (15) is to turn the
  above code into a multi-tasking program that
  handle batches of data
• Slides available but not tackled in class
  check web
• I was able to get things working with up to
  batches of 32 data points, but things went astray
  after that and I have not solved the problem.
• Lab. 5 demonstration together with short report
  explaining thread status diagrams