The EdX51 Operating System

The EdX51 operating system was designed as a teaching/learning tool. It provides operating system services to application programmers developing systems that run on 8051 microcontrollers and their derivatives. The OS was written in C using Keil’s µVision IDE together with Keil’s C51 compiler.

Depending on the configuration, EdX51 uses between 607 and 1676 bytes of code memory.

The scheduler is cooperative and tasks have quasi-priority that is fixed at compile time. There is no task preemption. A task runs until it blocks. Once it blocks, the scheduler hands the CPU to the first ready task it finds in the list of tasks.

EdX51 provides a semaphore service, a message queue service and a watchdog timer service. These features can be easily removed if they are not required, thereby saving code and data memory.

Version 1.3.1 includes changes to the way tasks register and unregister with the watchdog timer.