Subversion Repositories HelenOS-doc

    <section>

      <title>Lazy FPU Context Switching</title>

      <para>Implementing lazy FPU switching on MIPS architecture is

      straightforward. When coprocessor CP1 is disabled, any FPU intruction

      raises a Coprocessor Unusable exception. The generic lazy FPU context

      switch is then called that takes care of the correct context

      save/restore.</para>

    </section>

    <para>PowerPC allows kernel to enable mode, where data and intruction

    memory reads are not translated through virtual memory mapping

    (<emphasis>real mode</emphasis>). The real mode is automatically enabled

    when an exception occurs. However, the kernel uses the same memory

    structure as on other 32-bit platforms - physical memory is mapped into

    the top 2GB, userspace memory is available in the bottom half of the

    32-bit address space.</para>

    <section>

      <title>OpenFirmware Boot</title>

      <para>The OpenFirmware loads an image of HelenOS operating system and

      passes control to the HelenOS specific boot loader. The boot loader then

      performs following tasks:</para>

      <itemizedlist>

        <listitem>

          <para>Fetches information from OpenFirmware regarding memory

          structure, device information etc.</para>

        </listitem>

        <listitem>

          <para>Switches memory mapping to the real mode.</para>

        </listitem>

        <listitem>

          <para>Copies the kernel to proper physical address.</para>

        </listitem>

        <listitem>

          <para>Creates basic memory mapping and switches to the new kernel

          mapping, in which the kernel can run.</para>

        </listitem>

        <listitem>

          <para>Passes control to the kernel <function>main_bsp</function>

          function.</para>

        </listitem>

      </itemizedlist>

    <section>

      <title>Thread Local Storage</title>

      <para>Although thread local storage is not officially supported in

      statically linked binaries, GCC supports it without any major obstacles.

      As a thread pointer is designated register r13, the thread local data

      section starts at an address r13+16.</para>

        </figure></para>