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<?xml version="1.0" encoding="UTF-8"?>
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<?xml version="1.0" encoding="UTF-8"?>
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<chapter id="hardware">
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<chapter id="hardware">
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  <?dbhtml filename="hardware.html"?>
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  <?dbhtml filename="hardware.html"?>
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  <title>Device drivers</title>
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  <title>Device Drivers</title>
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  <para>Since HelenOS is a microkernel, a framework for supporting userspace
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  <para>Since HelenOS is a microkernel, a framework for supporting userspace
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  device drivers has been implemented. A typical userspace task acting as a
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  device drivers has been implemented. A typical userspace task acting as a
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  device driver might need to: </para>
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  device driver might need to:</para>
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  <itemizedlist>
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  <itemizedlist>
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    <listitem>
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    <listitem>
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      <para>receive notifications about interrupts sent by its device,</para>
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      <para>receive notifications about interrupts sent by its device,</para>
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    </listitem>
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    </listitem>
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      <para>control preemption.</para>
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      <para>control preemption.</para>
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    </listitem>
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    </listitem>
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  </itemizedlist>
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  </itemizedlist>
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  <section>
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  <section>
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    <title>Interrupt notifications</title>
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    <title>Interrupt Notifications</title>
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    <para>Userspace tasks that are in hold of the
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    <para>Userspace tasks that are in hold of the
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    <constant>CAP_IRQ_REG</constant> capability can register themselves via
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    <constant>CAP_IRQ_REG</constant> capability can register themselves via
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    the <code>ipc_register_irq()</code> to be notified about occurrences of a
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    the <code>ipc_register_irq()</code> to be notified about occurrences of a
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    given interrupt. The registration call takes two arguments. The first
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    given interrupt. The registration call takes two arguments. The first
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    when the interrupt handler performs certain reads or writes of memory or
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    when the interrupt handler performs certain reads or writes of memory or
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    I/O space.</para>
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    I/O space.</para>
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  </section>
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  </section>
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  <section>
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  <section>
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    <title>Accessing memory and I/O space</title>
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    <title>Accessing Memory and I/O Space</title>
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    <para>When a task has the <constant>CAP_MEM_MANAGER</constant> capability,
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    <para>When a task has the <constant>CAP_MEM_MANAGER</constant> capability,
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    it can use the <constant>SYS_MAP_PHYSMEM</constant> to map regions of
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    it can use the <constant>SYS_MAP_PHYSMEM</constant> to map regions of
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    physical memory to its address space. When successful, the syscall creates
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    physical memory to its address space. When successful, the syscall creates
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    an address space area for the physical memory region. The address space
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    an address space area for the physical memory region. The address space
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    only on architectures that have separate I/O space (e.g. amd64 and
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    only on architectures that have separate I/O space (e.g. amd64 and
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    ia32).</para>
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    ia32).</para>
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  </section>
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  </section>
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  <section>
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  <section>
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    <title>Disabling preemption</title>
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    <title>Disabling Preemption</title>
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    <para>It might be desirable for a device driver to temporarily disable
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    <para>It might be desirable for a device driver to temporarily disable
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    preemption. Tasks that can do this are required to have the
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    preemption. Tasks that can do this are required to have the
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    CAP_PREEMPT_CONTROL capability. Preemption could be theoretically disabled
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    CAP_PREEMPT_CONTROL capability. Preemption could be theoretically disabled
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    by disabling interrupts on the current processor, but disabling preemption
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    by disabling interrupts on the current processor, but disabling preemption