Your Electronics Open Source

According to a survey in Embedded System Design, more than a quarter of embedded systems now in development won't have an OS at all. None. a little over 28% of all our survey-takers said the system they're designing now won't have so much as a tiny scheduler or task switcher.

Main Software Loop

In this design, the software simply has a loop. The loop calls subroutines, each of which manages a part of the hardware or software. This method is called round-robin. The round-robin method is very popular in small microcontrollers.

Interrupt Controlled System

Some embedded systems are predominantly interrupt controlled. This means that tasks performed by the system are triggered by different kinds of events. An interrupt could be generated for example by a timer in a predefined frequency, or by a serial port controller receiving a byte.

These kinds of systems are used if event handlers need low latency and the event handlers are short and simple. Usually these kinds of systems run a simple task in a main loop also, but this task is not very sensitive to unexpected delays.

Sometimes the interrupt handler will add longer tasks to a queue structure. Later, after the interrupt handler has finished, these tasks are executed by the main loop. This method brings the system close to a multitasking kernel with discrete processes.

Most of above shedulers or kernels are developed in house. They are simple and easy-to-use. They are not RTOS because they are only sheduler part of an OS. A complete OS includes scheduler, task switching and resource allocation, memory management.

Non Real Time Embedded OS

Not every embedded operation systems are designed for real-time, for example, Windows CE is not a real-time OS, but it is a multi-tasking OS. But you know, as time goes by, things change a lot. These OSes are improved by using real-time kernels or patches.

A lot of similiar OSes have already faded out. Such as PPSM from Motorola (for its 68K/ARM DragonBall CPU), Zaurus from Sharp. The propertiary OS for TX MIPS micro from Toshiba (Sorry I forgot name of OS, but it was popular in Toshiba's Taiwanese customers)...

Palm OS, running on Motorola/Freescale 68K based Dragonball CPU and ARM9 CPU, Development tools available freely from official web site and 3rd parties.

EPOC/Symbian, supports ARM CPU. leader in mobile phone market.