EE 319K Introduction to Embedded Systems

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EE 319KIntroduction to Embedded Systems

• Lecture 11 Data Acquisition,Numerical
  Fixed-Point Calculations, Lab 8

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Agenda

• Recap
• Sampling, Nyquist
• Analog to Digital Conversion
• Agenda
• Exam 2
• Pointers, Array and String Manipulation, FSMs
• Data acquisition
• Numerical fixed-point calculations
• Lab 8

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Exam 2 review

• 0) Being able to quickly design, implement, and
  debug assembly software
• 1) Understanding differences between data and
  address, being able to use pointers and indices
• 2) Understanding differences between 8-bit,
  16-bit data and 32-bit data
• 3) Understanding differences between signed and
  unsigned integers
• 4) Programming if-then if-then-else for-loops
  while-loops and do-while-loops in assembly
• 5) Processing a variable-length array or string,
  either size first or terminating code at end
• 6) Addition subtraction multiplication and
  division

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Exam 2 review

• 7) Shift left and right (signed and unsigned)
• 8) Call by value, call by reference, return by
  value
• 9) AAPCS Program conventions
• Save and restore R4-R11,LR if you wish to modify
• Parameter passing in registers R0,R1,R2,R3
• All input parameters promoted to 32 bits
• Return parameter in R0
• 10) Implementation of FSM using a linked data
  structure or using a table structure with an
  index
• Mealy and Moore
• Not a real port, so no bit-specific addressing
• Read modify write sequences to be friendly
  (including input pin)
• 11) Accessing arrays and strings using pointers
  and indices
• Stepping through two or more arrays at a time
• 8/16/32-bit data, signed/unsigned numbers

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Exam 2 review

• A) You may be given one or more variable length
  arrays of data, bufi
• The size may be the first entry
• There may be a termination code
• The data may be 8-bit ASCII characters or
  integers
• The integers may be 8 16 or 32 bits
• Integers may be signed or unsigned
• A pointer to this array may be passed in R0
• You may be asked to deal with special cases
  size0, size too big, overflow

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Exam 2 Array problems

• Determine the size of the array
• Return the first element of the array
• Find the maximum or minimum element in an array
• Find the sum of all the elements
• Find the average of all the elements
• Find the mode of all the elements
• Find the range maximum - minimum
• Find the maximum or minimum slope
  (bufi1-bufi)
• Find the maximum or minimum absolute value
• Count the number of times a particular value
  occurs (bufi1000)
• Search for the occurrence of one string in
  another
• Concatenate two strings together
• Delete characters from a string
• Insert one string into another
• Move data from one place to another within an
  array or string
• Sort the array (we will give the steps)

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Exam 2 FSM problems

• Convert a FSM graph to a linked data structure or
  table with an index
• Write a Mealy FSM controller (with or without
  timer wait)
• Write a Moore FSM controller (with or without
  timer wait)
• It also may involve accessing a linked structure
  like Lab 5

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Exam 2

• Runs on your laptop
• Keil in simulation (no board)
• During exam Keil, Keil help, PC calculator
• Needs internet to download and upload
• Battery power
• Written in assembly (no C)
• No SysTick, no interrupts
• Overall grade a combination of
• Numerical score from grader
• Program style (reviewed later)
• Tricking the grader is considered bad

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Data Acquisition System (Lab 8)

• Hardware
• Transducer
• Electronics
• ADC

• Software
• ADC device driver
• Timer routines
• Output compare interrupts
• LCD driver
• Measurement system
• How fast to update
• Fixed-point number system
• Algorithm to convert ADC into position

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Analog Input Device

• Transducer A device actuated by power from one
  system that supplies power in the same or other
  form to another system.

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Transducer Circuit

• Position to voltage

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Data Acquisition System

• Data flow graph

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Data Acquisition System

• Call graph

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Thread Synchronization in Lab 8
Background thread
Foreground thread

• SysTick ISR
• Sample ADC
• Store in ADCmail
• Set ADCstatus

• Main loop
• Wait for ADCstatus
• Read ADCmail
• Clear ADCstatus
• Convert to distance
• Display on LCD

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Sampling Jitter

• Definition of time-jitter, dt
• Let n?t be the time a task is scheduled to be run
  and tn the time the task is actually run
• Then dtn tn n?t
• Real time systems with periodic tasks, must have
  an upper bound, k, on the time-jitter
• -k dtn k for all n

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Measurement

• Resolution Limiting factors
• Transducer noise
• Electrical noise
• ADC precision
• Software errors
• Accuracy Limiting factors
• Resolution
• Calibration
• Transducer stability

Average accuracy (with units of x)
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Fixed-Point Revisited

• Why
• express non-integer values
• no floating point hardware support (want it to
  run fast)
• When
• range of values is known
• range of values is small
• How
• 1) variable integer, called I.
• may be signed or unsigned
• may be 8, 16 or 32 bits (precision)
• 2) fixed constant, called ? (resolution)
• value is fixed, and can not be changed
• not stored in memory
• specify this fixed content using comments

value ? integer ?
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Fixed-Point Numbers

• The value of the fixed-point number
• Fixed-point number ? I?
• Smallest value Imin D, where Imin is the
  smallest integer
• Largest value Imax D, where Imax is the
  largest integer
• Decimal fixed-point, ?10m
• Decimal fixed-point number I 10m
• Nice for human input/output
• Binary fixed-point, ?2m
• Binary fixed-point number I 2m
• Easier for computers to perform calculations

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Fixed-Point Math Example

• Consider the following calculation.
• C 2?R
• The variables C, and R are integers
• 2p 6.283
• C (6283R)/1000

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Fixed-Point Math Example

• Calculate the volume of a cylinder
• V ?R2 L
• The variables are fixed-point
• R I2-4 cm L J2-4 cm
• V K2-8 cm3 2p 2012-5
• K (201IIJ)gtgt9

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Make a Voltmeter with ADC
Vin (V) Analog in N Digital out I (1 mV) Variable part LCD
0 0 0 0.000
0.75 1024 750 0.750
1.5 2048 1500 1.500
2.25 3072 2250 2.250
3 4096 3000 3.000
?0.001 V Vin 3N/4096 how ADC works Vin I
0.001 definition of fixed point I
(3000N)/4096 substitution I (mNb)/ 4096
calibrate to get m and b
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Lab 8 Calibration