SE-3910 Real-time Systems Week 4, Class 1 Quick-Quiz (Ungraded!) CS2852 5/22/2019 SE-3910 Real-time Systems Week 4, Class 1 Quick-Quiz (Ungraded!) Lab 3 due Friday, Week 4 Lab 4 due Tuesday, Week 5 Exams in C CPU Speed CPU Utilization Polling vs. Interrupts SE3910 Class 2-3 Yoder PPT notes Spring 2014 Print 1, 9, 12, 14 Well-Known Ports 20 Generate I/O Materials Generate Pin Materials For Tuesday Lab: Quiz Lab Safety Checkout Tentative Class Objectives: Explain why writing a file causes a pin to “light” Explain why reading a file reads a 3.3/0V value from a pin Create programs using file I/O Create new capabilities for the GPIO library Create new kernel modules for the BeagleBone? - Because it’s cool - To give deeper hardware/software understanding - To give familiarity with the whole beagle-bone process Explore the Beaglebone OS source code Explain key design decisions made by Beaglebone / Linux OS writers Contrast these decisions with Classic Linux and Windows decisions Old Stuff: In-class: Explain the concept of rise time and fall time. Make sketch or figure: Using the oscilloscope, measure the time difference between two signals. For HW/class activity: Classify events as either being synchronous or asynchronous, periodic, aperiodic, or sporadic Objectives: Explain the difference between an embedded and non-embedded system Explain the difference between a real-time system and a non-real-time system Identify the key components of the Beaglebone platform Explain why the Beaglebone changes operating frequency under different power conditions Identify the key hardware interfaces of the beaglebone Explain the concept of a cape (daughterboard) Calculate the software GPIO pin number from an expansion port header definition Understand how to read a basic schematic Explain the concept of a dropping resistor Explain the concept of a pull up and a pull down resistor Short the beaglebone’s output to ground Connect the input directly to 5V Connect the input through a resistor to 5V Discuss peak voltage again Potential Topics Piazza Link to Schilling’s PDF Slides At end: Discuss two kinds of interrupt systems: Idle main “background” main SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling, Some from Dr. Hornick, etc. Dr. Yoder

Whole-class Quiz! (1) Select all that are real-time systems Video Game CS2852 5/22/2019 Whole-class Quiz! (1) Select all that are real-time systems Video Game Aircraft Autopilot Refinery Process Control Cash Register Smartphone Discussion: Why do we pick these options? Are there any proceses that are not real-time? Why does the book re-define real-time systems? What are the practical implications? SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling Dr. Yoder

Whole-class Quiz! (2) Select all that are embedded systems Video Game CS2852 5/22/2019 Whole-class Quiz! (2) Select all that are embedded systems Video Game Aircraft Autopilot Refinery Process Control Cash Register Smartphone Discussion: What is the key difference between an embedded system and a non-embedded system? Does this clarify our answers? SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling Dr. Yoder

Whole-class Quiz! (3) Where do I find GPIO 49? CS2852 5/22/2019 Whole-class Quiz! (3) Where do I find GPIO 49? SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling Dr. Yoder

CPU Speed Fact: Question: CS2852 5/22/2019 CPU Speed Fact: The Beaglebone can operate at 275 MHz, 500 MHz, 600 MHz, or 720 MHz http://beaglebone.cameon.net/home/set-cpu-speed Question: Why should I care? Depending on discussion, model transistor as “capacitor” Or simply discuss “switching” cost Switches/s * energy/switch = power (energy/time) SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling Dr. Yoder

Tasking What happens when the CPU runs out of tasks to process? What should I do about it? (Give at least two possible answers.) SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling

Utilization Factor Formal Definition How to compute % non-idle processing How to compute ui = ei/pi ei – execution time, worst case pi – execution period SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling

Question How should I set the utilization factor? SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling

Utilization Factor Theory: See Ch. 3 (from Laplante and Ovaske 4E, p. 12) SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling

What is the Zone Type for this system? CS2852 5/22/2019 A system has 4 processes, as is described below. What is the overall utilization? Task 1: Measure wheel slip (p1=100ms, e1=12ms) Task 2: Measure traction capabilities of wheel (p2=50ms, e2=5ms) Task 3: Monitor system diagnostics (p3=200ms, e3=5ms) Task 4: Send system messages over network (p4=25ms, e4=1ms) What is the Zone Type for this system? Supposing overloaded, how do we fix it? Also, what other “bottlenecks” might cause us to miss deadlines? SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling Dr. Yoder

Question while(true) { } How can we make task1() more punctual? CS2852 5/22/2019 Question while(true) { task1() task2() task3() } How can we make task1() more punctual? SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling Dr. Yoder

Switch de-bouncing How can we avoid multiple presses? SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling

(Board code) CS2852 5/22/2019 Do on board. SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling Dr. Yoder

Interrupt Definitions CS2852 5/22/2019 Interrupt Definitions Interrupt An event in hardware that triggers the processor to jump from its current program counter to a specific point in the code. Interrupt Service Routine (ISR) The function that is called or the particular assembly code that is executed when the interrupt happens is called the Interrupt Service Routine (ISR). Interrupt flag (IFG) this is the bit that is set that triggers the interrupt, leaving the interrupt resets this flag to the normal state. Interrupt Enable Control bit that tells the processor that a particular interrupt should or should not be ignored. Interrupt Vector Table A table in memory which maps ISRs to interrupts. SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling Dr. Yoder