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Smr3143 – ICTP & IAEA (Aug. & Sept. 2017)

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Fernando Rincón

fernando.rincon@uclm.es

Introduction to Petalinux Smr3143 – ICTP & IAEA (Aug. & Sept. 2017) 2

Contents

• Embedded OS
• Embedded Linux
• Linux Architecture

Introduction to Petalinux Smr3143 – ICTP & IAEA (Aug. & Sept. 2017) 3

Embedded OS

• Embedded systems usually perform very simple tasks

– Monitor status of sensors – React to events following simple rules

• Move motors
• Activate relays
• Send data
• …
• Complex applications may have more requirements

– Concurrent execution – Real-time management – Resource multiplexion – Advanced communication mechanisms

• Purpose of the OS → Release the user from those complex tasks

Introduction to Petalinux Smr3143 – ICTP & IAEA (Aug. & Sept. 2017) 4

Desktop vs Embedded

• Main diferences

– Small footprint, and tailored to the specifc need – Custom peripheral drivers. – Less protection mechanisms

• Even no Memory management Unit (MMU)

– Real-time – Lack of very simplistic user-interface – Sometimes no network connection

• Although the trend is to have everything connected

Introduction to Petalinux Smr3143 – ICTP & IAEA (Aug. & Sept. 2017) 5

Embedded OS Development

• Cross-development

– Host machine: develoment enviroment and tools

• Cross-compiler

– Diferent versions for bare-metal and OS development

• Mostly because of the linked libraries
• Ex: arm-none- vs arm-xilinx-linux
• Target root flesystem & basic libraries for compilation purposes

– Target machine:

• Bootloader
• Kernel
• Root flesystem
• Cross-platform design cycle

– Compile → test → debug – Use of emulators

• Bootstrap process:

– Flash – Network – ...

Introduction to Petalinux Smr3143 – ICTP & IAEA (Aug. & Sept. 2017) 6

Why Linux?

• Low cost of ownership
• Open-source, full control and customizability
• Rich feature set
• Quality of Linux components
• Re-use of Linux components
• Big active developer community & resources
• Pool of talented embedded Linux developers
• Scalability, from embedded to the cluster
• Standard tools and run-time environment

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What does Linux Ofer?

• Multiple processor achitectures supported

– ARM, MIPS, PowerPC, x84, amd64, Microblaze, …

• Reduced foot print (a few MB) and fast booting times (~4 s)
• Networking:

– full support for TCP/IP, Wif, Bluetooth, USB, …

• Graphics:

– X, Frame Bufer & DRM/KMS. – Graphical development libraries QT, Gnome, …

• Multimedia:

– Video4Linux & Gstreamer, FFMPeg, OpenCV, …

Introduction to Petalinux Smr3143 – ICTP & IAEA (Aug. & Sept. 2017) 8

What Does Linux Ofer?

• Interoperability and OS infrastructure

– Networking, fle systems, device support – Scheduling, processes/threads, interrupt handling, interprocess

communication, symmetric multiprocessing (SMP)

• Developer familiarity

– Standard tools – Standard run-time environment – Application code can be prototyped on the desktop

• Scalability

– Deeply embedded → single board computers → desktop → server → cluster

• Freedom and openness

– Accessibility to modify source code

Introduction to Petalinux Smr3143 – ICTP & IAEA (Aug. & Sept. 2017) 9

Linux Components

Hardware QEMU Libraries – Graphics, Video, Networking, etc. Application Utilities User Applications

Root File system (rootfs)

U-boot First Stage Boot Loader

Boot Loader

Linux Kernel Device Drivers

Kernel Image Board Support Package (BSP): Collection of SoC/board specific Linux components that include Linux kernel & device drivers, boot loader and tools

Linux Build & Development Tool GNU Cross-Compiler tool chain & Debugger

Tools

Linux Build tools: PetaLinux, Yocto, OpenEmbedded, buildroot Other tool chains: Linaro, GCC mainline

Introduction to Petalinux Smr3143 – ICTP & IAEA (Aug. & Sept. 2017) 10

Anatomy of a Linux System

• User applications

– Task specifc – Libraries – C run time, networking, – graphics, for example

• Kernel

– More on this soon

• Hardware

– CPU, memory – Timer, interrupt controller, I/O

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Linux Kernel Architecture Overview

• System call interface (SCI)

– Function calls from user space to

kernel

• Process management

– Processes or threads – Share the CPU between the active

threads

• Memory management

– Manages the virtual and physical

memory

• Virtual fle system

– Switching layer between the SCI

and the fle systems supported by Linux

Introduction to Petalinux Smr3143 – ICTP & IAEA (Aug. & Sept. 2017) 12

Linux Kernel Architecture Overview

• Network stack

– Above TCP, socket layer – Invoked through the SCI

• Device drivers

– Supports most of the common

devices

• Architecture-dependent code

(BSP)

– Processor and platform-specifc

code

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System Call Interface

• Contract between user space and kernel space

– Request services – Memory, I/O – Process management

• The standard C library is a wrapper around the system call interface

– For example, malloc()

is a C library call

• Maintains a pool of memory
• Calls kernel memory allocator only when that pool is exhausted

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Virtual Memory

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Linux distributions