11-1 Bard, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi EE 319K Introduction to...

11-1Bard, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi

EE 319KIntroduction to Embedded Systems

Lecture 11: Data Acquisition,Numerical Fixed-Point Calculations,

Lab 8

11-2

Agenda

RecapSampling, NyquistAnalog to Digital Conversion

AgendaExam 2

o Pointers, arrays, strings, structures, FSMsData acquisitionNumerical fixed-point calculationsLab 8

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

11-3

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, division, shift, and, or, xor

http://users.ece.utexas.edu/~valvano/Volume1/Exam2thoughts.pdf

11-4

Exam 2 review

7) Structures 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 table structure with an index Moore Not a real port, so no bit-specific addressing, no timer Read modify write sequences to be friendly (including

input pin) 11) Accessing arrays strings and structures using pointers and

indices Stepping through two or more arrays at a time 8/16/32-bit data, signed/unsigned numbers

No FSM Spring 2015

11-5

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 codeThe data may be 8-bit ASCII characters or

integersThe integers may be 8 16 or 32 bitsIntegers may be signed or unsignedA pointer to this array may be passed in R0 You may be asked to deal with special cases:

size=0, size too big, overflow

11-6

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)

11-7

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

No FSM Spring 2015

11-8

Exam 2

Runs on your laptopKeil in simulation (no board)During exam: Keil, Keil help, PC calculatorNeeds internet to download and uploadBattery power

Written in assembly (no C)No SysTick, no interruptsOverall grade a combination of

Numerical score from graderProgram style (reviewed later)

Tricking the grader is considered dishonestHard-coding answers is considered dishonest

11-9

Data Acquisition System (Lab 8)

HardwareTransducerElectronicsADC

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


11-10

Analog Input Device

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


11-11

Transducer Circuit

Position to voltage


11-12

Data Acquisition System

Data flow graph


PositionSensor

Voltage0 to +3.3V

ADChardware

ADCdriver

Sample0 to 4095

SysTickISR

Sample0 to 4095

SysTickhardware

LCDdisplay

LCDdriver Fixed-point

0 to 2.000

Position0 to 2 cm

main

Mailbox

ST7735

11-13

Data Acquisition System

Call graph


main

SysTickhardware

SysTick

LCDhardware

LCDdriver

ADChardware

ADC driver

ISR

In

Init ST7735

11-14

Thread Synchronization in Lab 8

SysTick ISRSample ADCStore in ADCmailSet ADCstatus

Main loopWait for ADCstatusRead ADCmailClear ADCstatusConvert to distanceDisplay on LCD

Background thread Foreground thread

Other calculationsRead datafrom input

Full

Empty

Mainprogram

ISR

Process MailStatus = Empty

Status Mail = dataStatus = Full

a

bc

d


11-15

Sampling Jitter

Definition of time-jitter, δt:Let nΔt be the time a task is scheduled to be

run and tn the 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 all n


11-16

Measurement

Resolution: Limiting factorsTransducer noiseElectrical noiseADC precisionSoftware errors

Accuracy: Limiting factorsResolutionCalibrationTransducer stability

Measurement Output

pdf

100 measurements with Position = P1 100 measurements with

Position= P1+PP

Average accuracy (with units of x) =

n

imiti xx

n 0

1


11-17

Fixed-Point Revisited Why:

express non-integer valuesno floating point hardware support (want it to run fast)

When:range of values is knownrange of values is small

How:1) variable integer, called I.

may be signed or unsignedmay be 8, 16 or 32 bits (precision)

2) fixed constant, called (resolution)value is fixed, and can not be changednot stored in memoryspecify this fixed content using comments

value integer •


11-18

Fixed-Point Numbers

The value of the fixed-point number:Fixed-point number I•

Smallest value = Imin • , where Imin is the smallest integer

Largest value = Imax • , 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

b-1 b-2 b-3 b-4 b-5 b-6b9 b8 b7 b6 b5 b4 b3 b2 b1 b0

Fixed binary point


11-19

Fixed-Point Math Example

Consider the following calculation. C = 2**R

The variables C, and R are integers 2 ≈ 6.283

C = (6283*R)/1000


11-20

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 2 ≈ 201*2-5

K = (201*I*I*J)>>9


11-21

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 = 3•N/4096 how ADC worksVin = I • 0.001 definition of fixed pointI = (3000*N)/4096 substitution I = (m•N+b)/ 4096 calibrate to get m and b


Make a Voltmeter with ADC

11-22

Lab 8 Calibration


Position Analog input ADC sample Correct Fixed-point Measured Fixed-point Output 0.10 cm 0.432 538 100 84 0.40 cm 1.043 1295 400 421 0.80 cm 1.722 2140 800 797 1.20 cm 2.455 3050 1200 1202 1.40 cm 2.796 3474 1400 1391

n

imiti xx

n 0

1

11-1 Bard, Tiwari, Telang, Janapa Reddi, Gerstlauer, Valvano, Yerraballi EE 319K Introduction to...

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