Subversion Repositories HelenOS-doc

Rev

Rev 40 | Rev 48 | Go to most recent revision | Show entire file | Ignore whitespace | Details | Blame | Last modification | View Log | RSS feed

Rev 40 Rev 45
Line 3... Line 3...
3 
  <?dbhtml filename="arch.html"?>
 3 
  <?dbhtml filename="arch.html"?>
4 
 
 4 
 
5 
  <title>Architecture overview</title>
 5 
  <title>Architecture overview</title>
6 
 
 6 
 
7 
  <section>
 7 
  <section>
8 
    <title>Scheme</title>
 8 
    <para>
9 
 
 - 
 
10 
    <para><mediaobject id="arch1">
 9 
      <mediaobject id="arch1">
11 
        <imageobject role="html">
 10 
        <imageobject role="html">
12 
          <imagedata fileref="images/arch1.png" format="PNG" />
 11 
          <imagedata fileref="images/arch1.png" format="PNG" />
13 
        </imageobject>
 12 
        </imageobject>
14 
 
 13 
 
15 
        <imageobject role="fop">
 14 
        <imageobject role="fop">
16 
          <imagedata fileref="images.vector/arch1.svg" format="SVG" />
 15 
          <imagedata fileref="images.vector/arch1.svg" format="SVG" />
17 
        </imageobject>
 16 
        </imageobject>
18 
      </mediaobject></para>
 17 
      </mediaobject>
19 
  </section>
 - 
 
20 
 
 - 
 
21 
  <section>
 - 
 
22 
    <title>Kernel primitives</title>
 - 
 
23 
 
 - 
 
24 
    <para><termdef><glossterm>Thread</glossterm> is the basic execution
 - 
 
25 
    primitive.</termdef></para>
 - 
 
26 
 
 - 
 
27 
    <para><termdef><glossterm>Thread context</glossterm> represents state of
 - 
 
28 
    the <emphasis>thread</emphasis>. Thread context is built of the context
 - 
 
29 
    registers contents, FPU state and the stack.</termdef></para>
 - 
 
30 
 
 - 
 
31 
    <para><termdef><glossterm>Task</glossterm> is a multi-purpose entity,
 - 
 
32 
    serving to incorporate set if its threads, provide common address space to its threads,
 - 
 
33 
    be an end-point in IPC.</termdef></para>
 - 
 
34 
 
 - 
 
35 
    <para><termdef><glossterm>Address space area</glossterm> is a mutually
 - 
 
36 
    disjunctive range of memory with the code, stack and data.
 - 
 
37 
    </termdef></para>
 - 
 
38 
 
 - 
 
39 
    <para><termdef><glossterm>Address space</glossterm> is a aggregating
 - 
 
40 
    entity for address space areas, connecting them to the task.
 - 
 
41 
    </termdef></para>
 - 
 
42 
  </section>
 - 
 
43 
 
 - 
 
44 
  <section>
 - 
 
45 
    <title>Monolithic microkernel</title>
 - 
 
46 
 
 - 
 
47 
    <para>Though HelenOS was initially planned as a microkernel, we were
 - 
 
48 
    trying to avoid several issues, connected with microkernels, such as much
 - 
 
49 
    higher overhead during memory management and hardware operations. For this
 - 
 
50 
    reason some of the subsystems, that are to be implemented as servers in
 - 
 
51 
    classic microkernel design, were implemented as a part of kernel, thus
 - 
 
52 
    minimizing this overhead.</para>
 - 
 
53 
 
 - 
 
54 
    <formalpara>
 - 
 
55 
      <title>Memory management</title>
 - 
 
56 
 
 - 
 
57 
      <para>HelenOS has all its memory
 - 
 
58 
      management functionality in the kernel, available to the memory
 - 
 
59 
      management server via the set of syscalls.</para>
 - 
 
60 
    </formalpara>
 - 
 
61 
 
 - 
 
62 
    <formalpara>
 - 
 
63 
      <title>Kernel device drivers</title>
 - 
 
64 
 
 - 
 
65 
      <para>HelenOS kernel has some of the very basic device drivers
 - 
 
66 
      <itemizedlist>
 - 
 
67 
          <listitem>
 - 
 
68 
            ACPI
 - 
 
69 
          </listitem>
 - 
 
70 
 
 - 
 
71 
          <listitem>
 - 
 
72 
            APIC
 - 
 
73 
          </listitem>
 - 
 
74 
 
 - 
 
75 
          <listitem>
 - 
 
76 
            SMP configuration
 - 
 
77 
          </listitem>
 - 
 
78 
 
 - 
 
79 
          <listitem>
 - 
 
80 
            System clock
 - 
 
81 
          </listitem>
 - 
 
82 
 
 - 
 
83 
          <listitem>
 - 
 
84 
            Interrupt controllers
 - 
 
85 
          </listitem>
 - 
 
86 
 
 - 
 
87 
          <listitem>
 - 
 
88 
            Console and frame buffer
 - 
 
89 
          </listitem>
 - 
 
90 
 
 - 
 
91 
        </itemizedlist></para>
 - 
 
92 
    </formalpara>
 18 
    </para>
93 
  </section>
 - 
 
94 
 
 - 
 
95 
  <section>
 - 
 
96 
    <title>IPC</title>
 - 
 
97 
 
 - 
 
98 
    <para>HelenOS IPC is designed in analogy with telephone communication.
 - 
 
99 
    Each task has an <emphasis>answerbox</emphasis> and a set of
 - 
 
100 
    <emphasis>phones</emphasis> to call another tasks' answerboxes.</para>
 - 
 
101 
 
 - 
 
102 
    <para>Communication is possible after the connection is established, and
 - 
 
103 
    can be either <emphasis>asynchronious</emphasis> or
 - 
 
104 
    <emphasis>synchronious</emphasis>.</para>
 - 
 
105 
  </section>
 19 
  </section>
106 
 
 20 
 
107 
  <section>
 21 
  <section>
108 
    <title>Functionality model</title>
 - 
 
109 
 
 - 
 
110 
    <para>As you know, microkernel design is very simple, just enough to
 22 
    <para>The HelenOS operating system is designed as a relatively small
111 
    provide communication facility for tasks. Most of the OS functionality is
 23 
    microkernel assisted with a set of userspace drivers and server tasks.
112 
    performed by server tasks, that are running in userspace. Thus most of the
 24 
    HelenOS is not very radical in what subsystems should or should not be
113 
    system calls in monolithic kernels, are the IPC calls on server tasks in
 25 
    implemented in the kernel - in some cases, both kernel and userspace
114 
    microkernels.</para>
 - 
 
115 
 
 - 
 
116 
    <para>Moreover, problems experience the device drivers. Running in the
 26 
    drivers exist. The reason for creating the system as a microkernel is
117 
    user space, device driver still needs to recieve interrupts and access
 27 
    prosaic. Even though it is initially more difficult to get the same level
118 
    hardware directly.</para>
 - 
 
119 
 
 - 
 
120 
    <para>This raises two major problems in microkernels: <orderedlist
 28 
    of functionality from a microkernel than it is in the case of a simple
121 
        numeration="loweralpha">
 29 
    monolithic kernel, a microkernel is much easier to maintain once the
122 
        <listitem>
 - 
 
123 
          What is the recipient address of the server (e.g. "memory manager" or a specific device driver) ?
 30 
    pieces have been put to work together. Therefore, the kernel of HelenOS,
124 
        </listitem>
 - 
 
125 
 
 - 
 
126 
        <listitem>
 - 
 
127 
          How this server task is going to access hardware or kernel while running in the user mode?
 31 
    as well as the essential userspace libraries thereof can be maintained by
128 
        </listitem>
 - 
 
129 
      </orderedlist></para>
 - 
 
130 
 
 - 
 
131 
    <formalpara id="intro_ns">
 - 
 
132 
      <title>Name server</title>
 32 
    only a few developers who understand them completely. In addition, a
133 
 
 - 
 
134 
      <para>As every microkernel, HelenOS has a "Name server" task with "well
 33 
    microkernel based operating system reaches completion sooner than
135 
      known" IPC address, that connects user task to any server just by the
 34 
    monolithic kernels as the system can be used even without some traditional
136 
      string service indentification.</para>
 35 
    subsystems (e.g. block devices, filesystems and networking).</para>
137 
    </formalpara>
 - 
 
138 
 
 36 
 
139 
    <formalpara id="intro_ddi">
 - 
 
140 
      <title>Device driver interface</title>
 37 
    <para>HelenOS is comprised of the kernel and userspace server tasks. The
141 
 
 - 
 
142 
      <para>Device drivers use special syscalls to map physical memory areas
 38 
    kernel provides scheduling, memory management and IPC. It also contains
143 
      into their address space, to map port regions (mostly ia32). Interrupts
 39 
    essential device drivers that control the system clock and other devices
144 
      are delivered to the device driver task by the standard IPC
 40 
    necessary to guarantee a safe environment. Userspace communicates with the
145 
      means.</para>
 41 
    kernel through </para>
146 
    </formalpara>
 - 
 
147 
  </section>
 42 
  </section>
148 
</chapter>
 43 
</chapter>
149 

            44