The knowings and experiences of a group of developers.

Micro Operating System Overview, Port to AVR32

In this post I’m going to talk about the operating system that I made with the help of Sorcha. This post is the second on the AVR32 for dummies post series.

So the Micro Operating System or MOS is a simple, source readable operating system, or I believe so xD.

MOS is in C++ and divided in three main layers, System, Kernel and HAL (Hardware Abstraction Layer):

The System layer is the operating system development API, just like any operating system this layer is “responsible” for the application portability, by having all the possible software and hardware abstraction. This description of the System layer is my future goal, today this layer has little code base and little device drivers support.

The Kernel layer is where all my operating system knowledge is into. The kernel is based in two infra-structures that I studied before, eCos and user-threads.
The Kernel layer is divided in three sub-layers, InterruptController, Threading and Concurrent.

  • The Concurrent sub-layer is where all the synchronization primitives are implemented, things like atomic operations and synchronizers.
  • The Threading sub-layer is responsible for the Threads handling, it contains only two classes UThread and UScheduler.
  • The InterruptController is where the system delegate interrupt handling and treatment.

The HAL layer is the only one that knows what kind of hardware the system is running on. This layer is yet divided by two sub-layers, Target and Architecture Abstraction.

  • The Target Abstraction, is the only software component that knows on witch specific hardware the system is running on, so this sub-layer is responsible for all the hardware configuration and management.
  • The Architecture Abstraction is the sub-layer that knows on what kind of architecture the system is running. This sub-layer implements all system operations that it can, things like enable and disable interrupts, boot loaders, interrupt traps and the context switch.

Today MOS only supports ARM7 architecture. There is some LPC2xxx device drivers on it, and only ran on a development board the yaab2294 (LPC2294 with 8mb ram/rom expansion).

But that is about to change, with this port to AVR32 the operating system will be in two different architectures, processors and boards \o/.

The only thing I need to do is port the HAL layer to the AVR32 architecture and to my board (EVK1104, UC3 processor). In the next posts I’m going to talk more specifically on what is needed to do to port mos to another architecture and board.

MOS doesn’t have a pretty programming interface yet, but where’s some of it’s features:

  • Clean code, based on managed languages conventions (mainly C#) so that managed programmers don’t run away when they see the first code lines.
  • The synchronization don’t disable interrupts, that’s a cool feature made with a global system lock (a counter) that prevents interrupt treatment to change system global variables or switch threads.
  • Delegation on interrupt service routines, when an interrupt treatment is heavy, it’s possible to delegate that work to system defined thread, by doing so, the system is “always” susceptible to interrupts.

Final Comments

The MOS source code is available on github and I’ve created a new branch for the AVR32 port, in here.
This operating system is my way to apply all the concepts that I learned studying embedded and PC OSs and migrate my software design skills from managed to unmanaged.


One response to “Micro Operating System Overview, Port to AVR32

  1. Pingback: AVR32 First Contact, First Code « Imagination Overflow

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