Embedded Linux

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Overview

Embedded Linux is the name given to the Linux operating system when it is run on resource-constrained systems, as opposed to traditional laptop, desktop or server style computers.

Differences With “Standard” Linux

Embedded devices typically have fewer resources and hardware than a traditional computer running Linux. For example, embedded Linux might run on a single-board MCU which does not have a screen, harddrive or speakers. The board will usually have far less ROM and RAM than a traditional computer.

Because of the resource/hardware constraints, the embedded Linux kernel is usually stripped of all unneeded features, resulting in a much smaller ROM/RAM footprint.

Functionality Of MCUs

A MCU designed to run embedded Linux (or any other high-level operating system) usually has some (or most) of the following features:

• CPU (e.g. a ARM A9)
• MMU (if no MMU is present, a special type of Linux has to be run)
• Memory interface
• Graphics processor
• Ethernet
• USB
• UART interface
• SPI interface
• I2C interface
• CAN interface
• Analogue-to-digital converters (ADCs)
• Timers
• General purpose IO (GPIO)
• Watchdog timer (WDT)
• JTAG

Development Kits

2 of the most popular embedded Linux development kits are the RaspberryPi and the BeagleBone.

BusyBox

BusyBox is a bunch of stripped down Linux tools that are compiled into one executable. This makes it a popular choice for embedded devices, as each separate executable on an embedded system requires a significant amount of overhead.

Embedded ABI

An embedded application binary interface (EABI) is very similar to a normal ABI. It specifies:

• File formats
• Data types
• Register usage
• Stack frame organisation