CT420 Realtime Systems Dr. Hugh Melvin/Dr. Michael Schukat Room 406/402 Ext 3716/2031 hugh.melvin@nuigalway.ie michael.schukat@nuigalway.ie See Web resources Dr. Hugh Melvin, Discipline of IT, NUI,G 1 Course Structure 2 hrs lectures / week for both semesters Wed 9-11 IT304 Semester 1 Structured and unstructured labs Assignments Lab based work Technical Reports Linux/Windows based Dr. Hugh Melvin, Discipline of IT, NUI,G 2 Course Structure Content updated Course development in realtime! Subject to change Lecture notes on web in advance of lectures Assessment Exam + Assignments Typically 70/30 split Site Visit? Moneypoint (ESB) / Shannon ATC / Aer Lingus Dr. Hugh Melvin, Discipline of IT, NUI,G 3 1
Main Textbooks Real-Time Systems, Krisha & Shin, McGraw Hill Real-Time Systems Design & Analysis, Laplante, Wiley Programming for the Real World POSIX.4, Gallmeister, O Reilly Advanced Unix Programming, Rochkind, Addison Wesley Real-Time Systems & Programming Languages, Burns & Wellings, Pearson Dr. Hugh Melvin, Discipline of IT, NUI,G 4 Course Outline Classification of RTS Time Synchronisation for RTS Soft RTS Multimedia & Networks Scheduling for RTS Memory Management for RTS RT Programming Languages RTOS & POSIX.4 RT Fault Tolerance for RTS Dr. Hugh Melvin, Discipline of IT, NUI,G 5 RTS Definition of RTS? Difficult due to the extent and scope of RTS System where a substantial fraction of the design effort goes into making sure that deadlines are met (Krishna/Shin) Classification of RTS? Hard Firm Soft Differ by the consequences of missed deadlines Dr. Hugh Melvin, Discipline of IT, NUI,G 6 2
12:45:01 23:01:97 Dr. Hugh Melvin, Discipline of IT, NUI,G 7 Boiler Turbine Hard RTS VDU 1 BMS R30 Binary Field Inputs Binary Outputs Analogue Inputs Analogue Outputs AS101 AS112 Binary Field Inputs Binary Outputs Analogue Inputs Analogue Outputs AS013 AS017 Binary Field Inputs Binary Outputs Analogue Inputs Analogue Outputs AS131 AS133 VDU 2 VDU S\E s Office VDU Prog. Room Operators Keyboard 1 Operators Keyboard 2 S\E s Keyboard 1 Programmers Keyboard HW Analog Inputs HW Binary Inputs Annunciator Bus Coupler Tape Drive Storage Unit MEC-RT Data Storage Unit Bus 1 CS 275 Bus Bus 0 Printer 1 Printer 2 Printer Prog. Room Master Clock VDU 1 VDU 1 Local Printer VDU 1 VDU 2 5 1/4 FDD Storage Unit Alarms Printer Control Room VDU 2 VDU 3 Operator s Keyboard Fault Log Printer VDU 2 VDU 3 Operator s Keyboard Control Room LPA0 Local Terminals PG750 Maintenance Computer Operator s Annunciator Keyboard AS231 Unit Alarms System S\E s VDU & Keyboard MEC-RT Data Storage Unit Programming Room Printer MEC-RT Turbine Data Storage Unit Boiler OS254 Operations Programmers VDU & Keyboard Computer LPA1 VAX Maintenance Management System Dr. Hugh Melvin, Teleperm Discipline ME System of IT, Overview NUI,G 8 Unit 1 Unit 2 Unit 3 Bus 1 Bus 0 Bus 1 Bus 0 Bus 1 Bus 0 Bus A Bus Bus A Bus Bus A Bus Bus B Coupler Bus B Coupler Bus B Coupler Synogate Interface Synogate Interface Synogate Interface to to to Remote Operator OIS Server Station IBM NetFinity 5510 MP001 Gateway R30 Room Gateway Communications Room Station LAN MP002 Control Room Unit 1 Operator Station Control Room Unit 2 Control Room Unit 3 Operator Station Operator Station Dr. Hugh Melvin, Discipline of IT, NUI,G 9 3
Burner Management System Bus A Bus B N8 N8 1 2 3............ Non-Redundant Control Circuits 2 out of 3 Double Redundant Safety Circuits Triple Redundant Safety Circuits Dr. Hugh Melvin, Discipline of IT, NUI,G 10 Other Hard RTS Fly-by-wire control systems Robotics Medical Devices ABS / Airbag Protection Systems Dr. Hugh Melvin, Discipline of IT, NUI,G 11 Boeing 777 Dr. Hugh Melvin, Discipline of IT, NUI,G 12 4
Soft RTS: Multimedia Dr. Hugh Melvin, Discipline of IT, NUI,G 13 Firm RTS Somewhere in the middle? Eg. Private IP Network governed by SLA (Service Level Agreement) SLA specifies jitter/delay/loss/availability 99.999% Availability Lack of adherence results in : Poor customer satisfaction Penalties imposed on provider Consumer Devices Mobile phone / Cameras etc Dr. Hugh Melvin, Discipline of IT, NUI,G 14 Time Synchronisation for RTS Time of Day and Timing Two distinct issues Both often critical for RTS Synchronising 2v3 systems (timing) Precise data logging g for distributed system (time) Skew problems in POTS / VoIP / IPTV Clock Terminology Accuracy, Stability, Offset, Skew, Drift Synchronisation Algorithms Network Time Protocol (NTP) Limitations of conventional OS Timing Timer granularity & Time Services Dr. Hugh Melvin, Discipline of IT, NUI,G 15 5
Time UTC Evolved from Greenwich Mean Time GMT Time Synchronisation How closely 2 clocks agree on Time of Day Timing Relates to frequency Timing Synchronisation How closely 2 entities operate at same frequency Time & Timing Dr. Hugh Melvin, Discipline of IT, NUI,G 16 Greenwich Home of Time & the Prime Meridian Longitude 0 & GMT agreed in 1884 GMT driven by expansion of railways and need for national/international consistency Timeball rises and falls at 13.00 hrs Then site of London docks In service since 1833 Dr. Hugh Melvin, Discipline of IT, NUI,G 17 Greenwich Dr. Hugh Melvin, Discipline of IT, NUI,G 18 6
Dr. Hugh Melvin, Discipline of IT, NUI,G 19 Soft RTS: MM and Networks Real Time Communications Best Effort Internet default service Recent QoS Initiatives to differentiate between traffic streams Eg. Voice over IP Requires M2E delay typically < 150 msec Can cope with small degree of packet loss» Soft RTS How can delay/loss reqds be met? See ITU G.1010 Dr. Hugh Melvin, Discipline of IT, NUI,G 20 Mouth-to-Ear Delays Dr. Hugh Melvin, Discipline of IT, NUI,G 21 7
Real Time Communications LAN based developments Switched Networks (Embedded RTOS) Also Fast/Gigabit Ethernet : Overprovisioning? What Andy giveth, Bill taketh away! New difficulties for wireless environment Access Protocols CSMA WAN based developments IntServ DiffServ MPLS : Layer 2.5 Also development of RTP/RTCP/RTSP Protocols to support packet based MM traffic Dr. Hugh Melvin, Discipline of IT, NUI,G 22 Real Time Communications Endpoint Issues Increased complexity in terminals OS / Driver / Application Software / Hardware issues Increased delays due to complex and/or poorly written s/w Hardware Issues eg. skew = lack of synchronisation (timing) Dr. Hugh Melvin, Discipline of IT, NUI,G 23 Dr. Hugh Melvin, Discipline of IT, NUI,G 24 8
Clock Skew : Buffer Issues Dr. Hugh Melvin, Discipline of IT, NUI,G 25 Audio-System Clock Skew Dr. Hugh Melvin, Discipline of IT, NUI,G 26 RT Programming Languages Consider the following Fortran Loop statement DO 100 I=1,5 <block of text> 100 Continue but the following is also valid DO 100 I=1.5 <block of text> 100 Continue Fortran interpreted DO 100 I as a previously undeclared float variable assigned value 1.5 NASA mishap Ada is most recognised RT Prog. Lang. Boeing 777 control written in Ada Dr. Hugh Melvin, Discipline of IT, NUI,G 27 9
RTOS Windows / Unix / Linux Designed for time sharing of resources rather than meeting hard deadlines Designed for good average performance Not suited to Hard RTS typically Can be used after careful design considerations Examples M pt : User Interface provided by Linux/Win 2000» BUT not core control system Shannon ATC Unix powers main Thales ATC systems More suited to Soft RT functionality POSIX.4 improves RT performance of some OS Dr. Hugh Melvin, Discipline of IT, NUI,G 28 RTOS Hard RTS Good Average performance is of little use At 35000 ft when cabin pressure is lost When a Power station at full output is suddenly disconnected from the National Grid RTOS Can better meet RTS requirements Different design to conventional OS Scheduling/Process priorities are key issues VxWorks, QNX, Lynx, RTLinux, Cyclic Executive approach still widely used Software runs bare on hardware No OS! Used a lot with Soft RTS and some hard RTS Mobile phone OS: Symbian is market leader Dr. Hugh Melvin, Discipline of IT, NUI,G 29 Fault Tolerant Techniques Key Characteristic of Hard RTS 1. Fault-tolerance via Redundancy Full/Partial Fault Tolerance 2. Graceful degradation Eg.1: Citreon CX Common hydraulic system for Steering, Brakes and Suspension Order of failure?? Eg. 2: Power Plant Faulty sensor Alarm Overload AS station switch to manual but holds its state and will still respond to safety events/manual control 3. Failsafe operation Eg. Power Plant: Steam inlet valves spring loaded to shut on loss of power Many Hard RTS combine all 3 techniques Dr. Hugh Melvin, Discipline of IT, NUI,G 30 10
Citreon CX Dr. Hugh Melvin, Discipline of IT, NUI,G 31 Fault Tolerant Techniques Redundancy Hardware Redundancy Voting schemes Software Redundancy Code developed by different teams Often combined with hardware redundancy d Time Redundancy Build in time slack or roll back Information Redundancy Error Detection + Correction Note: TCP-IP based Error Detection via CRC relies on Time Redundancy for TCP traffic. Not acceptable for UDP based MM traffic Dr. Hugh Melvin, Discipline of IT, NUI,G 32 Fault Tolerant Techniques: Airbus 3 Main Flight Controllers 2 Backup Flight Controllers Software developed by different teams and on different platforms Seamless transfer Dr. Hugh Melvin, Discipline of IT, NUI,G 33 11
Fault Tolerant Techniques 1 2 3 DB-Out DB-Out DB-Out DB-In DB-In DB-In 2-out-of-3 2-out-of-3 2-out-of-3 ZV1 ZV2 ZV3 Unit Central 2-out-of-3 2-out-of-3 2-out-of-3 ZV1 ZV2 ZV3 RAM EPROM 1 RAM EPROM 2 RAM EPROM 3 Level 2-out-of-3 EAVn Inputs Extension Units Outputs Dr. Hugh Melvin, Discipline of IT, NUI,G 34 Course Outline Case Study Approach Assessment Assignment Possibilities Time Synchronisation Timing Services (Windows versus Linux) Internet Multimedia Scheduling Ada tutorial POSIX RT Features Dr. Hugh Melvin, Discipline of IT, NUI,G 35 Resources Various text books Research papers Websites Details will be posted on course website Possible site visits? ESB Moneypoint Shannon ATC Aer Lingus facility Dr. Hugh Melvin, Discipline of IT, NUI,G 36 12