Embedded Operating Systems for Real-Time Applications

Transcription

1 Embedded Operating Systems for Real-Time Applications Sagar P M ( ) Supervisor: Dr.Vivek Agarwal

2 INTRODUCTION Embedded system: hardware and software for specific function real-time embedded systems: have timing constraints Sagar PM 2

3 INSIDE AN EMBEDDED SYSTEM Processor Software ROM & RAM Inputs and outputs σ Keyboard σ Monitor Sagar PM 3

4 CRITICAL FEATURES Processing power Response Reliability Power consumption Number of units Expected lifetime Testability Sagar PM 4

5 WHAT IS AN OPERATING SYSTEM? Functions: Managing hardware & software resources Providing a Common Interface Types: = Single-user, single task : PalmOS = Single-user, multi-tasking : Windows98 = Multi-user : Unix = Real-time operating system: VxWorks Sagar PM 5

6 REAL -TIME OPERATING SYSTEMS RTOS : predictable to unpredictable events performance: correctness of logical result Types: the result delivery time Hard RT systems :deadlines are critical ( Aircraft flight control system) Soft RT systems:deadlines are not that critical ( communication systems ) Sagar PM 6

7 WHY RTOS? Applications becoming complex: ϖ meet the system response requirements ϖ to keep the development time reasonable Benefits: simplifies design process- split into tasks critical events - handled efficiently better use of the system resources Overheads : cost of the RTOS + the royalties per unit more RAM and ROM 2 to 4 % additional CPU overload Sagar PM 7

8 FEATURES YOU NEED IN A GOOD EMBEDDED RTOS Architecture : Client - server Process Server Client application Memory Server File Server Network Server Display Server Microkernel Hardware Microkernel (minimum OS) + server tasks Dynamic loading & unloading of modules Configurable & Scalable Switching times increases contd Sagar PM 8

9 FEATURES IN RTOS Process -Thread -Task model : Multi-tasking essential for real-time The application is divided into multiple tasks Thread : light-weight process faster switch Blocked Ready Running scheduler contd Sagar PM 9

10 FEATURES IN RTOS Scheduler: The heart and soul of an OS ϖ General OS: first-in-first-out ϖ RTOS : shortest job first round robin require a way to share the processor important tasks to grab the processor needs priority based scheduling algorithm Pre-emptive & Non Pre-emptive contd Sagar PM 10

11 FEATURES IN RTOS Task & Data : private data ( registers, stack ) shared data ( global, static) Task Synchronisation : Semaphores protect shared data signal events Message Mailboxes: pointer size variable Message Queues: array of mail boxes Event Flags: Boolean flags contd Sagar PM 11

12 FEATURES IN RTOS Interrupts: mechanism to signal an asynchronous event RTOS should have shortest ϖ Interrupt latencies ϖ Interrupt response times Memory management : access time - bound or predictable fast &predictable functions to allocate and free fixed size buffers Hard RT systems -static memory allocation Sagar PM 12

13 CASE STUDIES QNX RTOS v6.1 client-server based architecture 10 Kb micro-kernel + optional processes can be distributed over several nodes VRTX Pre-emptive scheduling Dynamic memory allocation is supported development and target system independent contd Sagar PM 13

14 CASE STUDIES Windows NT needs hard disk and a powerful processor Configuration and user interaction requires a dedicated screen and keyboard only 7 priority levels thread switch latency is high Sagar PM 14

15 CONCLUSIONS Ideal features of Embedded RTOS Open Source Portable ROM able Scalable & Configurable Multi-tasking Deterministic Memory Management Rich in Services Interrupt Management Sagar PM 15

16 Advanced Research in RTOS Need for general purpose architecture: flexible meet different requirements dedicated and matched to the application New operating systems and task designs : to support predictability high degree of adaptability Sagar PM 16

17 Thank You Sagar PM 17