Subversion Repositories HelenOS-doc

    <section>

        <title>Monolithic microkernel</title>

        <para>

            Though HelenOS was initially planned as a microkernel, we where trying to avoid several issues, connected

            with microkernels, such as much higher overhead during memory management and hardware operations. For this reason

            some of the subsytems, that are to be implmented as servers in classic microkernel design, where implemented

            as a part of kernel, thus minimizing this overhead.

        </para>

        <formalpara>

        <title>Memory management</title>

        <para>

            Unlike the classic microkernel, HelenOS has all its memory management functionality in the kernel, available to the memory

            management server via the set of syscalls.

        </para>

        </formalpara>

        <formalpara>

        <title>Kernel device drivers</title>

        <para>

            HelenOS kernel has some of the very basic device drivers

            <itemizedlist>

            <listitem>ACPI</listitem>

            <listitem>APIC</listitem>

            <listitem>SMP configuration</listitem>

            <listitem>System clock</listitem>

            <listitem>Interrupt controllers</listitem>

            <listitem>Console</listitem>

            <listitem>VESA &amp; frame buffer</listitem>

            </itemizedlist>

        </para>

        </formalpara>

    </section>

    <section>

        <title>Kernel primitives</title>

        <para>

        <termdef><glossterm>Thread</glossterm> is the basic execution primitive.</termdef>

        </para>

        <para>

        <termdef><glossterm>Thread context</glossterm> represents state of the <emphasis>thread</emphasis>. Contains registers state, FPU state, stack(s).</termdef>

        </para>

        <para>

        <termdef><glossterm>Task</glossterm> </termdef>

        </para>

        <para>

        <termdef>

            <glossterm>Address space area</glossterm> is a mutually disjunctive range of memory with the code, stack and data.

        </termdef>

        </para>

        <para>

        <termdef>

            <glossterm>Address space</glossterm> is a aggregating entity for address space areas, connecting them to the task.

        </termdef>

        </para>             1

    </section>

    <section>

        <title>IPC</title>

        <para>

            Due to the high intertask communication traffic, IPC becomes critical subsystem for microkernels, putting high demands on the

            speed, latency and reliability of IPC model and implementation. HelenOS IPC is designed in analogy with telephone communication.

            Each task has an <emphasis>answerbox</emphasis> and a set of <emphasis>phones</emphasis> to call another tasks' answerboxes. Communication

            is possible after the link establishment, and can be either <emphasis>asynchronious</emphasis> or <emphasis>synchronious</emphasis>.

         </para>

    </section>