ElectRoidWarE: 2013-10-20

Emulator for Embedded Linux

Target Emulation and Virtual Machines

Virtualization is a mature technology that lets several operating systems share the physical resources of a machine, such that that each thinks it has exclusive use of the resources. Emulation means that a program impersonates another—or, in this case, that a processor impersonates another. Cygwin is software that emulates a POSIX system on a Windows machine.

However, when you’re emulating a processor different than the host, you have fewer options. Emulating a different processor requires software that, in effect, translates the op-codes of the emulated processor into the op-codes for the host processor.

Real Time Configuration for Embedded System

Real Time

A system is real time when timeliness is a dimension of correctness; that means a correct answer delivered late is the same as an answer that has never been delivered. Real-time systems abound in the real world. To a degree, all systems are real time, because they have real-world deadlines: an airline ticketing program needs to issue tickets before the plane leaves, for example.

Real-time systems that can tolerate missing an occasional deadline, with a reduction in

performance or quality of output, are known as soft real-time systems.

On a hard real-time system, a missed deadline has serious consequences: when a deadline is missed, a saw may cut at the wrong angle; or a flow-control valve may not close, resulting in flooding.

Application Development Environment on Linux

Configuring the Application Development Environment

Embedding Python

To use Python in an embedded project, you must build the Python virtual machine for the target. That virtual machine is built with a cross-compiler. To build Python, you need a cross-compiler built as explained in the previous chapter with the glibc library, but you can’t use the uClibc C library to build the Python virtual machine. First, obtain and download the source code:

$ wget http://www.python.org/ftp/python/<version>/Python-<version>.tgz

$ tar xzf Python-<version>.tgz

Installing BusyBox on Linux

BusyBox

BusyBox is an open source project that is a key part of many embedded systems. It supplies limited functionality implementations of most of the command-line executables found on a desktop Linux system; BusyBox calls these applets. What the applets lack in functionality is more than compensated for in their size: a complete, full-featured BusyBox system weighs in at 1.5MB and can be much smaller when unused applets are dropped.

Download the Software

The BusyBox project resides at www.busybox.net, and the www.busybox.net/download.html page contains a history of releases and any follow-on patches. As an example, you’ll use the 1.14.1 release on this page, but understand that the release will be different by the time this book makes it to press:

Booting the Board in embedded system

Booting the Board

The Boot Loader

A boot loader isn’t unique to Linux or embedded systems. It’s a program first run by a computer so that a more sophisticated program can be loaded next. In a Linux system, two boot loaders usually run before the Linux kernel starts running. The code also populates a data structure that you can view by doing the following after the system is up and running: