Editing Embedded system (section)

===Preemptive multitasking or multi-threading===
In this type of system, a low-level piece of code switches between tasks or threads based on a timer invoking an interrupt. This is the level at which the system is generally considered to have an operating system kernel. Depending on how much functionality is required, it introduces more or less of the complexities of managing multiple tasks running conceptually in parallel.

As any code can potentially damage the data of another task (except in systems using a [[memory management unit]]) programs must be carefully designed and tested, and access to shared data must be controlled by some synchronization strategy such as [[message queue]]s, [[semaphore (programming)|semaphores]] or a [[non-blocking synchronization]] scheme.

Because of these complexities, it is common for organizations to use an off-the-shelf RTOS, allowing the application programmers to concentrate on device functionality rather than operating system services. The choice to include an RTOS brings in its own issues, however, as the selection must be made prior to starting the application development process. This timing forces developers to choose the embedded operating system for their device based on current requirements and so restricts future options to a large extent.<ref>
{{cite web
|url=http://www.clarinox.com/docs/whitepapers/Whitepaper_06_CrossPlatformDiscussion.pdf |archive-url=https://web.archive.org/web/20110219200027/http://www.clarinox.com/docs/whitepapers/Whitepaper_06_CrossPlatformDiscussion.pdf |archive-date=2011-02-19 |url-status=live
|title= Working across Multiple Embedded Platforms
|publisher=clarinox
|access-date=2010-08-17
}}</ref> 

The level of complexity in embedded systems is continuously growing as devices are required to manage peripherals and tasks such as serial, USB, TCP/IP, [[Bluetooth]], [[Wireless LAN]], trunk radio, multiple channels, data and voice, enhanced graphics, multiple states, multiple threads, numerous wait states and so on. These trends are leading to the uptake of [[embedded middleware]] in addition to an RTOS.