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EE 319K Introduction to Embedded Systems

EE 319K Introduction to Embedded Systems. Lecture 11: Data Acquisition, Numerical Fixed-Point Calculations, Lab 8. Agenda. Recap Sampling, Nyquist Analog to Digital Conversion Agenda Exam 2 Pointers, Array and String Manipulation, FSMs Data acquisition Numerical fixed-point calculations

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EE 319K Introduction to Embedded Systems

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  1. EE 319KIntroduction to Embedded Systems Lecture 11: Data Acquisition,Numerical Fixed-Point Calculations, Lab 8 Bard, Gerstlauer, Valvano, Yerraballi

  2. 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 Bard, Gerstlauer, Valvano, Yerraballi

  3. 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

  4. 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

  5. Exam 2 review • A) You may be given one or more variable length arrays of data, buf[i] • 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: size=0, size too big, overflow

  6. 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 (buf[i+1]-buf[i]) • Find the maximum or minimum absolute value • Count the number of times a particular value occurs (buf[i]==1000) • 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)

  7. 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

  8. 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

  9. 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 Data Acquisition System (Lab 8) Bard, Gerstlauer, Valvano, Yerraballi

  10. Analog Input Device • Transducer – A device actuated by power from one system that supplies power in the same or other form to another system. Bard, Gerstlauer, Valvano, Yerraballi

  11. Transducer Circuit • Position to voltage Bard, Gerstlauer, Valvano, Yerraballi

  12. P o s i t i o n V o l t a g e S a m p l e 0 t o 2 c m 0 t o + 3.3V 0 t o 4 0 9 5 S a m p l e P o s i t i o n A D C 0 t o 4 0 9 5 A D C S e n s o r h a r d w a r e d r i v e r S y s T i c k I S R S y s T i c k M a i l b o x h a r d w a r e m a i n L C D L C D d i s p l a y F i x e d - p o i n t d r i v e r 0 t o 2 . 0 0 0 Data Acquisition System • Data flow graph Bard, Gerstlauer, Valvano, Yerraballi

  13. Data Acquisition System • Call graph Bard, Gerstlauer, Valvano, Yerraballi

  14. 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 Bard, Gerstlauer, Valvano, Yerraballi

  15. Sampling Jitter • Definition of time-jitter,δt: • LetnΔt be the time a task is scheduled to be run and tnthe time the task is actually run • Then δtn= tn – nΔt • Real time systems with periodic tasks, must have an upper bound,k, on the time-jitter • -k ≤ δtn≤ +k for alln Bard, Gerstlauer, Valvano, Yerraballi

  16. 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) = Bard, Gerstlauer, Valvano, Yerraballi

  17. 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•  Bard, Gerstlauer, Valvano, Yerraballi

  18. 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 Bard, Gerstlauer, Valvano, Yerraballi

  19. Fixed-Point Math Example Consider the following calculation. C = 2**R The variables C, and R are integers 2p ≈ 6.283 C = (6283*R)/1000 Bard, Gerstlauer, Valvano, Yerraballi

  20. Fixed-Point Math Example Calculate the volume of a cylinder V = *R2 *L The variables are fixed-point R = I*2-4 cm L = J*2-4 cm V = K*2-8 cm3 2p ≈ 201*2-5 K = (201*I*I*J)>>9 Bard, Gerstlauer, Valvano, Yerraballi

  21. Make a Voltmeter with ADC =0.001 V Vin = 3•N/4096 how ADC works Vin = I • 0.001 definition of fixed point I = (3000*N)/4096 substitution I = (m•N+b)/ 4096 calibrate to get m and b Bard, Gerstlauer, Valvano, Yerraballi

  22. Lab 8 Calibration Bard, Gerstlauer, Valvano, Yerraballi

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