vx works and interrupt service routines

7/31/2019 Vx Works and Interrupt Service Routines

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VxWorks Facilities


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Introduction

developed by Wind River Systems, is a RealTime Operating System (RTOS) used to developreal-time applications for embedded systems.

VxWorks is available for Windows and UNIX

platforms. It provides a Graphical User Interface (GUI) for

application development

It provides high performance for critical tasks,

such as scheduling, memory allocation,interrupt handling etc.


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The VxWorks Architecture

VxWorks RTOS runs on client-server architecture. main

components-

Microkernel: (aka wind)

necessary to limit kernel size

because of the memory

constraints in ES.

VxWorks libraries: Provide the

functions necessary to use the

kernel services.Modules: (aka Board Support

Packages (BSPs)) Enable VxWorks

to accommodate simple and

complex ES.


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VxWorks Facilities

High-Performance Real-time Kernel Facilities POSIX Compatibility

I/O System

Local File Systems

Shared-Memory Objects Virtual Memory

C++ Development Support

Utility Libraries

Performance Evaluation Tools Target Agent

Network Facilities


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High-Performance Real-time

Kernel Facilities

Multitasking facilities(real time apps haveindependent tasks, each having own thread

and system resources)Multitasking kernel ( wind) uses interrupt-

driven, priority-based task scheduling

Inter-task communicationsfacilities(allowtasks to coordinate and synchronize)the wind kernel also supplies message queues,

pipes, sockets, and signals


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POSIX CompatibilityPOSIX -the Portable Operating System Interface

is a set of standards under development byrepresentatives of the software community, working

under an ISO/IEEE charter, to support application

portability

All POSIX 1003.1b interfaces are available in Vxworks. asynchronous I/O

semaphores

message queues

memory management

queued signals

scheduling

clocks and timers


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I/O System

Provides uniform device-independent access to manykinds of devices: (basic I/O routines: creat( ),remove( ), open( ), close( ), read( ), write( ), andioctl( ). Higher-level I/O routines printf( ) and scanf( )routines are also provided. )

A fast and flexible ANSI C-compatible routines (suchas fopen( ), fclose( ), fread( ), fwrite( ), getc( ), andputc( ) )

Includes POSIX-compliant asynchronous I/O: a lib. ofroutines performing i/o operations with other taskactivities concurrently.

includes device drivers for serial communication,disks, RAM disks, tape devices etc


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Local File Systems

Includes several local file systems for use with blockdevices (disks)

devices all use a standard interface

Several different file systems on single VxWorks systempossible even at same time.

MS-DOS Compatible File System: dosFs

RT-11 Compatible File System: rt11Fs

Raw Disk File System: rawFs

SCSI Sequential File System: tapeFs

cdRomFs Alternative File Systems


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C++ Development Support

The iostream library and the standard templatelibrary

VxWorks Wrapper Class library

Tools.h++ library

Virtual Memory VxWorks provides both bundled and unbundled (VxVMI)

virtual memory support with MMU, including the ability

to make portions of memory read-only. Bundled virtual memory provides the ability to mark buffers

noncacheable.

Unbundled virtual memory provides the ability to make textsegments and the exception vector table read-only.


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Shared-Memory Objectsused for communication and synchronization

between tasks on different CPUs.

Shared semaphores can be used to synchronize

tasks on different CPUs as well as provide mutualexclusion to shared data structures.

Shared message queues allow tasks on multiple

processors to exchange messages.

Shared memory management is available to

allocate common data buffers for tasks on different

processors.


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Utility Libraries

set of subroutine libraries, reduces both developmenttime and memory requirements

Interrupt Handling Support : hardware interrupts andsoftware traps handled.

Watchdog Timers (A watchdog facility allows callersto schedule execution of their own routines afterspecified time delays. )

Message Logging (A simple message logging facility

allows applications to send error or status messagesto a logging task, which then formats and outputsthe messages to a system-wide logging device )


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CONT..

Memory Allocation (VxWorks supplies a memorymanagement facility useful for dynamically

allocating, freeing, and reallocating blocks of

memory from a memory pool. )

ANSI C(The ANSI C specification includes thefollowing libraries: assert, ctype, errno, float, limits,

locale, math, setjmp, signal, stdarg, stdio, stddef,

stdlib, string, and time.).

Other types are Linear and Ring Buffer Manipulations,Linked-List Manipulations.


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Performance Evaluation Tools

To understand and optimize the performanceof a real-time system

VxWorks also provides the spy utility, whichprovides CPU utilization information for eachtask: the CPU time consumed, the time spent atinterrupt level, and the amount of idle time.


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Target Agent

o The target agent follows the WDB (Wind DeBug)protocol

o At the target side, target runs as the VxWorks tasktWdbTask.

o The target server sends debugging requests to thetarget agent.

o The debugging requests often result in the targetagent controlling or manipulating other tasks in the

system.o The target server and agent communicate using the

network.


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Network Facilities

VxWorks provides "transparent" access to otherVxWorks and TCP/IP-networked systems.

MUX interface (supporting advanced features such asmulticasting, polled-mode Ethernet, and zero-copytransmission).

Sockets-compliant programming interface, remoteprocedure calls (RPC), SNMP (optional), remote file access(including NFS client and server facilities and a non-NFS facilityutilizing RSH, FTP, or TFTP).

All VxWorks network facilities comply with standard Internetprotocols.


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Interrupt Service Routines Interrupt routines in an RTOS must adhere to two

rules:

Mustnt call RTOS functions that might block the caller

-Violating this rule may affect response time and

may even cause deadlock. May not call any RTOS function that might cause

RTOS to switch tasks unless the RTOS knows that aninterrupt routine, and not a task is running.

-RTOS uses various mechanisms to learn thatinterrupt routine is working. Violation may allow RTOS toswitch to other task and the ISR may not complete fora long time, thus greatly affecting response time


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How Interrupt routine should work?

1. The interrupt routine interrupts the lower priority task2. Calls the RTOS to write a message to the mail box(legal under rule 1)3. When the interrupt routine exits, RTOS guides the microprocessorto continue with the original task or start a higher priority task.


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What would really happen??

1. The higher priority task is blocked on the mailbox2. As soon as the interrupt routine writes to the mailbox, RTOS

unblocks the higher priority task.3. The task that was running (ISR), is no longer the highest priorityready-to-run task.4. RTOS switches to the higher priority task, ISR couldnt be completeduntil later


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How interrupt routines do work?

1. RTOS intercepts all interrupts (start time) and then call the interrupt

routine.2. After routine writes to the mailbox, the RTOS knows to return to the

routine and not to any unblocked higher priority task.3. After the ISR is over, RTOS gets the control again and decide thenext task


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THANK YOU

vx works and interrupt service routines

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