L4 - RT Operating Systems

Question 1

What are the main tasks of an operating system?

Answer 1

An OS controls the computer’s resources and provides base upon which applications can be written.

Question 2

What is the difference between the extended machine and the resource manager?

Answer 2

• extended machine: easy to use hides technical details
• resource manager: provides allocation of processors, memory etc.

Question 3

User Space

Answer 3

use functionality provided by the OS (normal processors) not the same rights to access memory/hardware as the OS

Question 4

Kernel Space

Answer 4

unlimited access to all resources; kernel executes its services interaction with user space via system calls

Question 5

Define Cooperative Scheduling.

Answer 5

different processes in parallel; processes must cooperate with scheduler processor cannot be taken from a process. E.g.: MacOS pre9; Windows 95/98/ME

Question 6

What is Preemptive Scheduling?

Answer 6

In preemptive scheduling the processor can be forcibly taken from any running process in user and even kernel space. E.g.: LINUX; MacOS; Windows NT/XP/Vista/7

Question 7

Which type of scheduling do RTS mostly use today?

Answer 7

RTS use mostly preemptive scheduling.

Question 8

Name three requirements of Real Time Operating Systems (RTOS).

Answer 8

• stable around-the-clock operation;
• exact and predefined response times;
• parallel processes;
• multi-core and multi-CPU support;
• fast process-switching (lightweight process, real time interrupt handling
• support for I/O operations (dynamic binding to kernel)
• system API (e.g. POSIX)

Question 9

Name three different types of latency.

Answer 9

• interrupt latency: time needed between interruption and execution
• scheduling latency: time between execution of last instruction of ISR and execution of process which state was changed due to the interruption
• context switch latency: time between execution of last instruction and the next process

Question 10

What is the difference between monolithic kernel and microkernel?

Answer 10

• Monolithic (Linux; Windows): services (driver; file system; network stack) of the OS run in kernel space
• Microkernel (QNX; Symbian; OS X; PikeOS): basic functionality (Basic IPC; Virtual Memory; Scheduling) in kernel space other services in user space

Question 11

QNX architecture

Answer 11

In QNX only a minimal set of services contained in the kernel space (only communication; threading and synchronization). OS services and device drivers run in user space.

Question 12

Which company did develop VxWorks?

Answer 12

WindRiver / Intel.

Question 13

Name an advantage and disadvantage of Linux.

Answer 13

• insufficient timer resolution, virtual memory (non-deterministic) and non-preemptive kernel
• easy development, portability and good hardware support —> RTLinux (add Hardware Abstraction Layer)

Question 14

AUTOSAR

Answer 14

AUTOSAR is a successor of OSEK/VDX and aims to become an industry standard. It was developed by BMW; Bosch; Continental; DaimlerChrysler; VW; Siemens and consists out of a modular layered architecture with standardized interfaces.

Question 15

TinyOS

Answer 15

• components connected via interfaces
• optimized for sensor networks
• no separate OS
• kernel or memory management -> single shared stack static memory allocation
• concurrency model: processes only interrupted by events not processes; FIFO