Embedded LinuxTopicsWhat is LinuxWhy use LinuxLinux PortabilityWhy Linux for Embedded Systems?What is Embedded Linux?Implementation of Embedded LinuxGeneric Architecture of LinuxLinux and Real-TimeSlide 11Real-Time Work on LinuxSlide 13Architecture of Real-Time LinuxArchitecture of Real-Time Linux (contd.)File Systems in Embedded LinuxDistributions of Embedded LinuxTypes of Embedded Linux SystemsFlies in the OintmentGrowth of Embedded LinuxApplications of Embedded LinuxReferences1Embedded LinuxKamalesh SahaUniversity of North Carolina at Charlotte2 TopicsWhat is LinuxWhy Use Linux?Linux PortabilityWhat is Embedded Linux?Generic Architecture of LinuxWhat Is Real-Time Linux?Architecture of Real-Time LinuxFile Systems in Embedded LinuxWho Provides Embedded Linux ?References Kamalesh Saha3What is Linux Linux is a free Unix-type operating system that is causing a revolution in the computer world. The kernel maintained by Linus Torvalds with the assistance of developers around the world, this operating system in only a few short years is beginning to dominate markets worldwide. A key reason for this is its development under the GNU (GNU’s Not Unix) General Public License, meaning that the source code for Linux is freely available to everyone for the asking. Kamalesh Saha4Why use LinuxOpen SourceReliabilityScalabilitySecureSupports Virtually All Network Communication ProtocolsLarge pool of skilled developersFree software and toolsNo runtime license Kamalesh Saha5Linux PortabilityLinux provides great portability.The same Application Source Code is Used ForA Large number of processors and architectures.A Large number of Embedded Board Support Packages (BSP).A Large number of interfaces with device drivers available.Linux is able to runs the same applications on everything from a Linux based PDA to your desktop systems to your enterprise servers. Kamalesh Saha6Why Linux for Embedded Systems? Kamalesh Saha7 What is Embedded Linux?The Linux OS ported to an embedded system.Generally contain a smaller subset of functionality.Less services provided.Less memory required.Boots from ROM.No keyboard or mouse required.Special software developed to control embedded peripherals. (flash disks, touch screens, tiny displays) Kamalesh Saha8 Implementation of Embedded LinuxInitial Program Loader (IPL) Loads the kernel into memoryThe Kernel This is the heart of Linux operating System. Linux has a monolithic kernel.File System The Linux kernel mounts a root file system when booted. Kamalesh Saha9 Generic Architecture of Linux Kamalesh SahaRef: “Building Embedded Linux Systems” – Karim Yaghmour10Linux and Real-Time Is Linux Real-Time?NO, BUT…Why?Monolithic Kernel:: The Linux kernel allows a kernel task exclusive access to some data for long periods. This could delay the execution of any POSIX (Portable Operating System Interface for uniX) real-time task that needs access to that same data.Non Preemptable:: The Linux kernel does not preempt the execution of any task during system calls. If a low-priority process is in the middle of a system call and a message is received for a real-time process, the message will unfortunately be held in the queue until the system call completes, despite its low priority. Kamalesh Saha11Linux and Real-Time Resource Lock:: Linux makes high-priority tasks wait for low-priority tasks to release resources. For example, if any process allocates the last network buffer and a higher priority process needs a network buffer to send a message, the higher priority process must wait until some other process releases a network buffer before it can send its message.Priority Scheduling:: The Linux scheduling algorithm will sometimes give the most unimportant and “nicest” process a time slice, even in circumstances when a higher priority process is ready to execute. Kamalesh Saha12Real-Time Work on Linux Today Linux can provide Soft Real-Time Two Approaches to Real-Time LinuxModify Linux to include a Real-Time scheduler.Fixes the problems discussed previously.Put Regular Linux on top of a Real-Time operating system (RTOS). Kamalesh Saha13Real-Time Work on Linux Several Vendors are working on Real-Time solutions:MontaVista has a Real-Time kernel that they are trying to get accepted by the Linux Community.RTLinux provides a Real-Time kernel uses Linux a thread of the Real-Time OS.Lineo has implemented the Real Time Application Interface (RTAI) for Linux. Kamalesh Saha14 Architecture of Real-Time Linux Kamalesh SahaRef: Circuit Cellar Article15 Architecture of Real-Time Linux (contd.) Resource Kernel Kamalesh SahaRef: Issues for Making Linux Predictable by T. Nakajima, M. I. Asaki16 File Systems in Embedded Linux Supports a wide range of file systems:Log-based file systems (XFS, JFS, JFFS2, ReiserFS, ext3): favorites for servers.Traditional Unix file systems (minix, ext, ext2, UFS)Network file systems (NFS, Coda, AFS, DFS)DOS/Windows file systems (FAT16, FAT32, NTFS) Kamalesh Saha17 Distributions of Embedded LinuxMontaVista SoftwareLynuxWorksLineoInteresting AlternativeOnCore SystemsOthersRedHat Kamalesh Saha18 Types of Embedded Linux SystemsETLinux LEMLOAF uClinux uLinux ThinLinux Kamalesh Saha19Flies in the Ointment Kamalesh Saha20Growth of Embedded Linux Kamalesh Saha21Applications of Embedded Linux Kamalesh SahaEntertainment devicesPDARobot Smart PhoneEmbedded Single Board ComputerEmbedded Processor and System-on-Chip IC22References www.embeddedlinuxjournal.comwww.embedded-linux.orgwww.lineo.comwww.linux.orgwww.linuxdevices.comwww.lynuxworks.comwww.redhat.comwww.wikipedia.orgIssues for Making Linux Predictable by T. Nakajima, M. I. AsakiEmbedding Linux by Alex Lennon“Building Embedded Linux Systems” – Karim Yaghmour Kamalesh Saha23 Kamalesh
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