Linux on embedded systems
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Embedded Linux is the use of a Linux operating system in embedded computer systems such as mobile phones, personal digital assistants, media players, set-top boxes, and other consumer electronics devices, networking equipment, machine control, industrial automation, navigation equipment and medical instruments. According to survey conducted by Venture Development Corporation, Linux was used by 18% of embedded engineers.
Differences from other Linux operating systems
Unlike desktop and server versions of Linux, embedded versions of Linux are designed for devices with relatively limited resources, such as cell phones and set-top boxes. Due to concerns such as cost and size, embedded devices usually have much less RAM and secondary storage than desktop computers, and are likely to use flash memory instead of a hard drive. Since embedded devices serve specific rather than general purposes, developers optimize their embedded Linux distributions to target specific hardware configurations and usage situations. These optimizations can include reducing the number of device drivers and software applications, and modifying the Linux kernel to be a real-time operating system.
Instead of a full suite of desktop software applications, embedded Linux systems often use a small set of free software utilities such as busybox, and replace the glibc C standard library with a more compact alternative such as dietlibc, uClibc, or Newlib.
Linux has been ported to a variety of processors not suited for use as the processor of desktop or server computers, such as various CPUs including ARM, avr32, blackfin, cris, frv, h8300, m32r, m68k, mips, mn10300, powerpc, sh, or xtensa processors, as an alternative to using a proprietary operating system and toolchain.
The advantages of embedded Linux over other embedded operating systems include no royalties or licensing fees, a stable kernel, a support base that is not restricted to the employees of a single software company, and the ability to modify and redistribute the source code. The disadvantages include a comparatively larger memory footprint (kernel and root filesystem), complexities of user mode and kernel mode memory access and complex device drivers framework.
Special interest groups
Several industry groups have formed to foster use of Linux in embedded applications. These include: the CE Linux Forum, founded in 2003 to aid the inclusion of embedded features in the main Linux kernel branch; the Linux Foundation (formerly Open Source Development Labs); the Linux Phone Standards Forum, created in 2004 to pursue a standard applications environment for Linux-based mobile phones and "converged devices"; the LiMo Foundation, founded in 2006 by Motorola, NEC, Panasonic, Samsung, DoCoMo, and Vodafone to establish a set of interfaces and standard reference components to improve the third-party mobile phone developer base; and the San Francisco, California-based Embedded Linux Consortium, which, until its 2005 closure and transfer of operations to the Linux Foundation, included IBM, Intel, LynuxWorks, and others, and focused on application programming interface standardization. The Embedded Linux Consortium produced the ELCPS (Embedded Linux Consortium Platform Specification) which was intended as a guide to developers of embedded Linux devices as to what functionality should be included in order to provide a standard platform supporting application portability.
Commercial embedded hardware and platforms
- Motorola mobile telephones, generally based on MontaVista Linux, include the RAZR² V8, ROKR E2, ROKR E6, A780, E680, A910, A1200, U9, E8 and others
- Openmoko's Neo 1973 or FreeRunner
- Nokia's N810 N800 N770
- Linksys WRT54G version 4 or earlier
- Panasonic P901i
- NEC N901ic telephones
- Philips LPC3180
- UTstarcom [DV007]
- Digi Connect ME and ConnectCore modules
- gumstix basix, connex and verdex
- Cisco MDS and Nexus switches
- Panasonic Viera plasma TVs
- TomTom GPS navigation systems
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- Moblin project
- T2 SDE
- Pico ITX
- Internet Tablet OS
- Digi Connect ME
- Unison Operating System
- DSPnano RTOS
- Weinberg, Bill (July 2008). Uniting Mobile Linux Application Platforms (PDF). LinuxPundit.com. p. 18.