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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 Data acquisition Numerical fixed-point calculations Lab 8. Hardware Transducer Electronics ADC.

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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, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  2. Agenda Recap Sampling, Nyquist Analog to Digital Conversion Agenda Data acquisition Numerical fixed-point calculations Lab 8 Bard, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  3. 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, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  4. 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, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  5. Transducer Circuit • Position to voltage Bard, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  6. 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 ST7735 Bard, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  7. Data Acquisition System • Call graph ST7735 Bard, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  8. 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, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  9. 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, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  10. 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, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  11. 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, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  12. 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, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  13. 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, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  14. Fixed-Point Math Example Calculate the volume of a cylinder V = *R2 *L The variables are binary 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, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  15. 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, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

  16. Lab 8 Calibration Bard, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

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