Getting Started with Rtlinux
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Comparison of Contemporary Real Time Operating Systems
ISSN (Online) 2278-1021 IJARCCE ISSN (Print) 2319 5940 International Journal of Advanced Research in Computer and Communication Engineering Vol. 4, Issue 11, November 2015 Comparison of Contemporary Real Time Operating Systems Mr. Sagar Jape1, Mr. Mihir Kulkarni2, Prof.Dipti Pawade3 Student, Bachelors of Engineering, Department of Information Technology, K J Somaiya College of Engineering, Mumbai1,2 Assistant Professor, Department of Information Technology, K J Somaiya College of Engineering, Mumbai3 Abstract: With the advancement in embedded area, importance of real time operating system (RTOS) has been increased to greater extent. Now days for every embedded application low latency, efficient memory utilization and effective scheduling techniques are the basic requirements. Thus in this paper we have attempted to compare some of the real time operating systems. The systems (viz. VxWorks, QNX, Ecos, RTLinux, Windows CE and FreeRTOS) have been selected according to the highest user base criterion. We enlist the peculiar features of the systems with respect to the parameters like scheduling policies, licensing, memory management techniques, etc. and further, compare the selected systems over these parameters. Our effort to formulate the often confused, complex and contradictory pieces of information on contemporary RTOSs into simple, analytical organized structure will provide decisive insights to the reader on the selection process of an RTOS as per his requirements. Keywords:RTOS, VxWorks, QNX, eCOS, RTLinux,Windows CE, FreeRTOS I. INTRODUCTION An operating system (OS) is a set of software that handles designed known as Real Time Operating System (RTOS). computer hardware. Basically it acts as an interface The motive behind RTOS development is to process data between user program and computer hardware. -
Porting Embedded Systems to Uclinux
Porting Embedded Systems to uClinux António José da Silva Instituto Superior Técnico Av. Rovisco Pais 1049-001 Lisboa, Portugal [email protected] ABSTRACT Concerning response times, computer systems can be di- The emergence of embedded computing in our daily lives vided in soft and hard real time[26]. In soft real time sys- has made the design and development of embedded applica- tems, missing a deadline only degrades performance, unlike tions into one of the crucial factors for embedded systems. in hard real time systems. In hard real time systems, miss- Given the diversity of currently available applications, not ing a time constraint before giving an answer may be worse only for embedded, but also for general purpose systems, it than having no answer at all. An example of a soft real time will be important to easily reuse part, if not all, of these ap- system is a common DVD player. While good performance plications in future and current products. The widespread is desirable, missing time constraints in this type of system interest and enthusiasm generated by Linux's successful use only results in some frame loss, or some quirks in the user in a number of embedded systems has made it into a strong interface, but the system can continue to operate. This is candidate for defining a common development basis for em- not the case for hard real time systems. Missing a deadline bedded applications. In this paper, a detailed porting guide in a pace maker or in a nuclear plant's cooling system, for to uClinux using the XTran-3[20] board, an embedded sys- example, can lead to catastrophic scenarios! tem designed by Tecmic, is presented. -
Beej's Guide to Unix IPC
Beej's Guide to Unix IPC Brian “Beej Jorgensen” Hall [email protected] Version 1.1.3 December 1, 2015 Copyright © 2015 Brian “Beej Jorgensen” Hall This guide is written in XML using the vim editor on a Slackware Linux box loaded with GNU tools. The cover “art” and diagrams are produced with Inkscape. The XML is converted into HTML and XSL-FO by custom Python scripts. The XSL-FO output is then munged by Apache FOP to produce PDF documents, using Liberation fonts. The toolchain is composed of 100% Free and Open Source Software. Unless otherwise mutually agreed by the parties in writing, the author offers the work as-is and makes no representations or warranties of any kind concerning the work, express, implied, statutory or otherwise, including, without limitation, warranties of title, merchantibility, fitness for a particular purpose, noninfringement, or the absence of latent or other defects, accuracy, or the presence of absence of errors, whether or not discoverable. Except to the extent required by applicable law, in no event will the author be liable to you on any legal theory for any special, incidental, consequential, punitive or exemplary damages arising out of the use of the work, even if the author has been advised of the possibility of such damages. This document is freely distributable under the terms of the Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License. See the Copyright and Distribution section for details. Copyright © 2015 Brian “Beej Jorgensen” Hall Contents 1. Intro................................................................................................................................................................1 1.1. Audience 1 1.2. Platform and Compiler 1 1.3. -
Mmap and Dma
CHAPTER THIRTEEN MMAP AND DMA This chapter delves into the area of Linux memory management, with an emphasis on techniques that are useful to the device driver writer. The material in this chap- ter is somewhat advanced, and not everybody will need a grasp of it. Nonetheless, many tasks can only be done through digging more deeply into the memory man- agement subsystem; it also provides an interesting look into how an important part of the kernel works. The material in this chapter is divided into three sections. The first covers the implementation of the mmap system call, which allows the mapping of device memory directly into a user process’s address space. We then cover the kernel kiobuf mechanism, which provides direct access to user memory from kernel space. The kiobuf system may be used to implement ‘‘raw I/O’’ for certain kinds of devices. The final section covers direct memory access (DMA) I/O operations, which essentially provide peripherals with direct access to system memory. Of course, all of these techniques requir e an understanding of how Linux memory management works, so we start with an overview of that subsystem. Memor y Management in Linux Rather than describing the theory of memory management in operating systems, this section tries to pinpoint the main features of the Linux implementation of the theory. Although you do not need to be a Linux virtual memory guru to imple- ment mmap, a basic overview of how things work is useful. What follows is a fairly lengthy description of the data structures used by the kernel to manage memory. -
An Introduction to Linux IPC
An introduction to Linux IPC Michael Kerrisk © 2013 linux.conf.au 2013 http://man7.org/ Canberra, Australia [email protected] 2013-01-30 http://lwn.net/ [email protected] man7 .org 1 Goal ● Limited time! ● Get a flavor of main IPC methods man7 .org 2 Me ● Programming on UNIX & Linux since 1987 ● Linux man-pages maintainer ● http://www.kernel.org/doc/man-pages/ ● Kernel + glibc API ● Author of: Further info: http://man7.org/tlpi/ man7 .org 3 You ● Can read a bit of C ● Have a passing familiarity with common syscalls ● fork(), open(), read(), write() man7 .org 4 There’s a lot of IPC ● Pipes ● Shared memory mappings ● FIFOs ● File vs Anonymous ● Cross-memory attach ● Pseudoterminals ● proc_vm_readv() / proc_vm_writev() ● Sockets ● Signals ● Stream vs Datagram (vs Seq. packet) ● Standard, Realtime ● UNIX vs Internet domain ● Eventfd ● POSIX message queues ● Futexes ● POSIX shared memory ● Record locks ● ● POSIX semaphores File locks ● ● Named, Unnamed Mutexes ● System V message queues ● Condition variables ● System V shared memory ● Barriers ● ● System V semaphores Read-write locks man7 .org 5 It helps to classify ● Pipes ● Shared memory mappings ● FIFOs ● File vs Anonymous ● Cross-memory attach ● Pseudoterminals ● proc_vm_readv() / proc_vm_writev() ● Sockets ● Signals ● Stream vs Datagram (vs Seq. packet) ● Standard, Realtime ● UNIX vs Internet domain ● Eventfd ● POSIX message queues ● Futexes ● POSIX shared memory ● Record locks ● ● POSIX semaphores File locks ● ● Named, Unnamed Mutexes ● System V message queues ● Condition variables ● System V shared memory ● Barriers ● ● System V semaphores Read-write locks man7 .org 6 It helps to classify ● Pipes ● Shared memory mappings ● FIFOs ● File vs Anonymous ● Cross-memoryn attach ● Pseudoterminals tio a ● proc_vm_readv() / proc_vm_writev() ● Sockets ic n ● Signals ● Stream vs Datagram (vs uSeq. -
Rtlinux and Embedded Programming
RTLinux and embedded programming Victor Yodaiken Finite State Machine Labs (FSM) RTLinux – p.1/33 Who needs realtime? How RTLinux works. Why RTLinux works that way. Free software and embedded. Outline. The usual: definitions of realtime. RTLinux – p.2/33 How RTLinux works. Why RTLinux works that way. Free software and embedded. Outline. The usual: definitions of realtime. Who needs realtime? RTLinux – p.2/33 Why RTLinux works that way. Free software and embedded. Outline. The usual: definitions of realtime. Who needs realtime? How RTLinux works. RTLinux – p.2/33 Free software and embedded. Outline. The usual: definitions of realtime. Who needs realtime? How RTLinux works. Why RTLinux works that way. RTLinux – p.2/33 Realtime software: switch between different tasks in time to meet deadlines. Realtime versus Time Shared Time sharing software: switch between different tasks fast enough to create the illusion that all are going forward at once. RTLinux – p.3/33 Realtime versus Time Shared Time sharing software: switch between different tasks fast enough to create the illusion that all are going forward at once. Realtime software: switch between different tasks in time to meet deadlines. RTLinux – p.3/33 Hard realtime 1. Predictable performance at each moment in time: not as an average. 2. Low latency response to events. 3. Precise scheduling of periodic tasks. RTLinux – p.4/33 Soft realtime Good average case performance Low deviation from average case performance RTLinux – p.5/33 The machine tool generally stops the cut as specified. The power almost always shuts off before the turbine explodes. Traditional problems with soft realtime The chips are usually placed on the solder dots. -
Embedded GNU/Linux and Real-Time an Executive Summary
Embedded GNU/Linux and Real-Time an executive summary Robert Berger Embedded Software Specialist Stratigou Rogakou 24, GR-15125 Polydrosso/Maroussi, Athens, Greece Phone : (+ 30) 697 593 3428, Fax: (+ 30) 210 684 7881 email: [email protected] Abstract What is real-time and how can it be added to a plain vanilla Linux kernel[1]? Two fundamentally different approaches are described here. One approach attempts to patch the vanilla Linux kernel (PREEMPT_RT[2]) to achieve real-time functionality, while the other one utilizes a dual kernel architecture (RTAI[3], RTLinux/GPL[4], Xenomai[5], XM/eRTL[6], Real-Time Core[7], XtratuM[8], seL4[9], PaRTiKle[10],...), where Linux runs as the idle process on top of the real- time kernel. How do those approaches compare? At the time I started my quest for the holy grail of real-time Linux I hoped that it would be a clear decision wether to use p-rt or dk, but things seem to be less black and white than I initially thought. Bear with me to find out what changed my initial believes. 1 Introduction I would like to thank Nicholas Mc Guire, Paulo Montegazza, Philippe Gerum1 and Jan Kiszka from the dual kernel (dk) camp and Thomas Gleixner from the preempt-rt (p-rt) side as well as Paul E. McKenney and Carsten Emde for sharing their precious time with me to provide valu- able input and to review this paper. 2 Real-Time Real-Time has to do with time (timeliness), but most of all with determinism (predictability, time and event determinism). -
Table of Contents
TABLE OF CONTENTS Chapter 1 Introduction ............................................................................................. 3 Chapter 2 Examples for FPGA ................................................................................. 4 2.1 Factory Default Code ................................................................................................................................. 4 2.2 Nios II Control for Programmable PLL/ Temperature/ Power/ 9-axis ....................................................... 6 2.3 Nios DDR4 SDRAM Test ........................................................................................................................ 12 2.4 RTL DDR4 SDRAM Test ......................................................................................................................... 14 2.5 USB Type-C DisplayPort Alternate Mode ............................................................................................... 15 2.6 USB Type-C FX3 Loopback .................................................................................................................... 17 2.7 HDMI TX and RX in 4K Resolution ........................................................................................................ 21 2.8 HDMI TX in 4K Resolution ..................................................................................................................... 26 2.9 Low Latency Ethernet 10G MAC Demo .................................................................................................. 29 2.10 Socket -
IPC: Mmap and Pipes
Interprocess Communication: Memory mapped files and pipes CS 241 April 4, 2014 University of Illinois 1 Shared Memory Private Private address OS address address space space space Shared Process A segment Process B Processes request the segment OS maintains the segment Processes can attach/detach the segment 2 Shared Memory Private Private Private address address space OS address address space space space Shared Process A segment Process B Can mark segment for deletion on last detach 3 Shared Memory example /* make the key: */ if ((key = ftok(”shmdemo.c", 'R')) == -1) { perror("ftok"); exit(1); } /* connect to (and possibly create) the segment: */ if ((shmid = shmget(key, SHM_SIZE, 0644 | IPC_CREAT)) == -1) { perror("shmget"); exit(1); } /* attach to the segment to get a pointer to it: */ data = shmat(shmid, (void *)0, 0); if (data == (char *)(-1)) { perror("shmat"); exit(1); } 4 Shared Memory example /* read or modify the segment, based on the command line: */ if (argc == 2) { printf("writing to segment: \"%s\"\n", argv[1]); strncpy(data, argv[1], SHM_SIZE); } else printf("segment contains: \"%s\"\n", data); /* detach from the segment: */ if (shmdt(data) == -1) { perror("shmdt"); exit(1); } return 0; } Run demo 5 Memory Mapped Files Memory-mapped file I/O • Map a disk block to a page in memory • Allows file I/O to be treated as routine memory access Use • File is initially read using demand paging ! i.e., loaded from disk to memory only at the moment it’s needed • When needed, a page-sized portion of the file is read from the file system -
A Machine-Independent DMA Framework for Netbsd
AMachine-Independent DMA Framework for NetBSD Jason R. Thorpe1 Numerical Aerospace Simulation Facility NASA Ames Research Center Abstract 1.1. Host platform details One of the challenges in implementing a portable In the example platforms listed above,there are at kernel is finding good abstractions for semantically- least three different mechanisms used to perform DMA. similar operations which often have very machine- The first is used by the i386 platform. This mechanism dependent implementations. This is especially impor- can be described as "what you see is what you get": the tant on modern machines which share common archi- address that the device uses to perform the DMA trans- tectural features, e.g. the PCI bus. fer is the same address that the host CPU uses to access This paper describes whyamachine-independent the memory location in question. DMA mapping abstraction is needed, the design consid- DMA address Host address erations for such an abstraction, and the implementation of this abstraction in the NetBSD/alpha and NetBSD/i386 kernels. 1. Introduction NetBSD is a portable, modern UNIX-likeoperat- ing system which currently runs on eighteen platforms covering nine processor architectures. Some of these platforms, including the Alpha and i3862,share the PCI busasacommon architectural feature. In order to share device drivers for PCI devices between different platforms, abstractions that hide the details of bus access must be invented. The details that must be hid- den can be broken down into twoclasses: CPU access Figure 1 - WYSIWYG DMA to devices on the bus (bus_space)and device access to host memory (bus_dma). Here we will discuss the lat- The second mechanism, employed by the Alpha, ter; bus_space is a complicated topic in and of itself, is very similar to the first; the address the host CPU and is beyond the scope of this paper. -
Interprocess Communication
06 0430 CH05 5/22/01 10:22 AM Page 95 5 Interprocess Communication CHAPTER 3,“PROCESSES,” DISCUSSED THE CREATION OF PROCESSES and showed how one process can obtain the exit status of a child process.That’s the simplest form of communication between two processes, but it’s by no means the most powerful.The mechanisms of Chapter 3 don’t provide any way for the parent to communicate with the child except via command-line arguments and environment variables, nor any way for the child to communicate with the parent except via the child’s exit status. None of these mechanisms provides any means for communicating with the child process while it is actually running, nor do these mechanisms allow communication with a process outside the parent-child relationship. This chapter describes means for interprocess communication that circumvent these limitations.We will present various ways for communicating between parents and chil- dren, between “unrelated” processes, and even between processes on different machines. Interprocess communication (IPC) is the transfer of data among processes. For example, a Web browser may request a Web page from a Web server, which then sends HTML data.This transfer of data usually uses sockets in a telephone-like connection. In another example, you may want to print the filenames in a directory using a command such as ls | lpr.The shell creates an ls process and a separate lpr process, connecting 06 0430 CH05 5/22/01 10:22 AM Page 96 96 Chapter 5 Interprocess Communication the two with a pipe, represented by the “|” symbol.A pipe permits one-way commu- nication between two related processes.The ls process writes data into the pipe, and the lpr process reads data from the pipe. -
L4-Linux Based System As a Platform for EPICS Ioccore
L4-Linux Based System As A Platform For EPICS iocCore J. Odagiri, N. Yamamoto and T. Katoh High Energy Research Accelerator Organization, KEK ICALEPCS 2001, Nov 28, San Jose Contents Backgrounds Causes of latency in Linux kernel Real-time Linux and EPICS iocCore L4-Linux as a real-time platform Conclusions Backgrounds iocCore portable to multi-platforms in EPICS 3.14 Linux promising candidate for running EPICS iocCore runs on Linux OS Interface libraries POSIX 1003.1c (Pthread) POSIX 1003.1b (real-time extension) However, … POSIX real-time extensions Unpredictable latency Not for hard real-time applications Possible rare misses to the deadline Causes Not in the libraries but in the Linux kernel Causes of Latency Non-preempt-able kernel Possibly up to 100 ms or more Disabling of interrupts Typically, several hundreds of µs Address Space Switching Tens of µs Non-preempt-able Kernel Interrupt Kernel Latency High Priority Process Low Priority Process Interrupt Disabling unsigned long flags; save_flags(flags); cli(); /* critical section */ restore_flags(flags); Address Space Switching Page Directory x86x86 Table User Page Space Table Physical Page Kernel Space Impacts on the Latency Non-preempt-able Kernel Interrupt Disabling Address Space Switching Two Different Approaches Kernel-level tasks / real-time scheduler RTLinux RTAI … User-level processes / low latency Linux Low latency patches Preempt-able kernel … RTLinux / RTAI Definitely shortest latency! Several tens of µs Free from all of the three obstacles