Real Time Operating Systems Introduction to Real-Time Systems Course originally developed by Maj Ron Smith 17-Oct-151Dr. Alain Beaulieu

17-Oct-15 Dr. Alain Beaulieu Outline  Definitions  Applications of real-time computer systems  Lifecycles  An Example 2

17-Oct-15 Dr. Alain Beaulieu Definitions  Real-Time System: “A real-time system is a software system that maintains an ongoing and timely interaction with its environment” Bran Selic 3

17-Oct-15 Dr. Alain Beaulieu Definitions (cont’d)  Real-Time System: “We can think of real-time systems as those that react to external inputs and in a timely manner affect the environment in which they operate” Burns and Wellings 4

17-Oct-15 Dr. Alain Beaulieu Definitions (cont’d)  Real-Time System: “ any system in which the time at which output is produced is significant. This is usually because the input corresponds to some movement in the physical world, and the output has to relate to that same movement” The Oxford Dictionary of Computing 5

17-Oct-15 Dr. Alain Beaulieu Definitions (cont’d)  Key characteristics of all the definitions  timeliness  timeliness = correctness  interaction with its environment  hardware interfaces 6

17-Oct-15 Dr. Alain Beaulieu Definitions (cont’d)  Aren’t all computer systems real-time While almost all software does interface to hardware, Windows, Icons, Menus and Pointers (WIMP) programming is NOT considered real- time ? 7

17-Oct-15 Dr. Alain Beaulieu Definitions (cont’d)  Hard versus soft real-time  hard real-time systems require that strict time deadlines are met; the strictest are when an event must occur at time x, not just by time x.  in soft real-time systems timeliness of events is important but not necessarily critical. Often expressed as : x out of y events be on time, or by x time ± some slack 8

17-Oct-15 Dr. Alain Beaulieu Definitions (cont’d)  Real-time versus embedded software  most real-time software is “embedded” within some larger system, and is usually the de facto central nervous system.  therefore quite often real-time and embedded are used interchangeably when referring to the software of real-time systems. 9

17-Oct-15 Dr. Alain Beaulieu Applications of real-time systems  process control  nuclear power plant  chemical plant  production control  automobile assembly line  communication, command & control  air traffic control system  embedded systems  TV Satellite receiver 10

17-Oct-15 Dr. Alain Beaulieu Life Cycles of real-time systems  Small embedded commercial applications  typically one-shot  field and (hope to) forget  high multiples  cost driven efficiency requirements 11

17-Oct-15 Dr. Alain Beaulieu Life Cycles (continued)  Larger real-time systems (including most Military applications)  generally subject to constant change  very long life-cycles  expensive to maintain  robust designs are critical  Configuration management is a must  Integrated Logistics Support  Software support must be planned 12

17-Oct-15 Dr. Alain Beaulieu Examples of Some Real Real-Time systems  Low Level Air Defence ADATS  10 Computers – 10 CSCI (without the missiles)  4 Radar Computers  C16A, B, C, D  Data Processing Unit  Turret Electronic Unit  Interface Electronic Unit  Coast Mode Processor  Control Electronic Unit  Servo Electronic Unit  full MIL-STD-2167A 13

17-Oct-15 Dr. Alain Beaulieu 14

Examples of some Real-Time Systems Interface Elec Unit To Radar and other ADATS (network of 6 +AF-BCP) Serial Interface & Auto Scanner R/D Converter 16 Channels Resolvers GBA, LOSSA Discrete I/O 24/24 Bits TEUTAULEUECUMV PSSEU Mount Servo Elect Unit A/D Converter 16 Channels D/A Converter 24 Channels Analog I/P GBA, LOSSA Analog O/P SEU CDU Main Memory DPU CMP Clock and interrupts 16 channel 17-Oct Dr. Alain Beaulieu

17-Oct-15 Dr. Alain Beaulieu Some problems…  Several computer languages, C, Several Assembly Languages, Pascal  DPU was a 16 bit processor… when there was none. 4X4 bit-sliced computer  Cyclic Executive  No RTOS  End-To-End test two weeks DPU only  Cycle counting from Pulse Code Modulation (PCM) Dumps  It works but… 16

17-Oct-15 Dr. Alain Beaulieu What might go wrong when developing this type of software?  Requirements formulation / documentation  Design formulation / documentation  Test formulation / documentation / conduct  (Software engineering communication)  Schedulability on a single processor  Compatibility among systems  Support for long-term maintenance To name just a few 17

17-Oct-15 Dr. Alain Beaulieu Summary “Real-time and distributed systems (combined) design has proven to be one of the most difficult and intricate problems ever faced. This is primarily because of the complexity of the real world in which these systems operate. Their environment can be bewilderingly diverse, dynamic, and unpredictable - components fail at random, communications are corrupted, interruptions occur when they are most inappropriate, and so on.” Selic 18