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<?xml version="1.0" encoding="UTF-8"?>
<chapter id="architecture">
  <?dbhtml filename="arch.html"?>
 
  <title>Architecture overview</title>
 
  <section>
    <title>Scheme</title>
 
    <para><mediaobject id="arch1">
        <imageobject role="html">
          <imagedata fileref="images/arch1.png" format="PNG" />
        </imageobject>
 
        <imageobject role="fop">
          <imagedata fileref="images.vector/arch1.svg" format="SVG" />
        </imageobject>
      </mediaobject></para>
  </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>. Thread context is built of the context
    registers contents, FPU state and the stack.</termdef></para>
 
    <para><termdef><glossterm>Task</glossterm> is a multi-purpose entity,
    serving to incorporate set if its threads, provide common address space to its threads,
    be an end-point in IPC.</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>
  </section>
 
  <section>
    <title>Monolithic microkernel</title>
 
    <para>Though HelenOS was initially planned as a microkernel, we were
    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 subsystems, that are to be implemented as servers in
    classic microkernel design, were implemented as a part of kernel, thus
    minimizing this overhead.</para>
 
    <formalpara>
      <title>Memory management</title>
 
      <para>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 and frame buffer
          </listitem>
 
 
 
 
        </itemizedlist></para>
    </formalpara>
  </section>
 
  <section>
    <title>IPC</title>
 
    <para>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.</para>
 
    <para>Communication is possible after the connection is established, and
    can be either <emphasis>asynchronious</emphasis> or
    <emphasis>synchronious</emphasis>.</para>
  </section>
 
  <section>
    <title>Functionality model</title>
 
    <para>As you know, microkernel design is very simple, just enough to
    provide communication facility for tasks. Most of the OS functionality is
    performed by server tasks, that are running in userspace. Thus most of the
    system calls in monolithic kernels, are the IPC calls on server tasks in
    microkernels.</para>
 
    <para>Moreover, problems experience the device drivers. Running in the
    user space, device driver still needs to recieve interrupts and access
    hardware directly.</para>
 
    <para>This raises two major problems in microkernels: <orderedlist
        numeration="loweralpha">
        <listitem>
          What is the recipient address of the server (e.g. "memory manager" or a specific device driver) ?
        </listitem>
 
        <listitem>
          How this server task is going to access hardware or kernel while running in the user mode?
        </listitem>
      </orderedlist></para>
 
    <formalpara id="intro_ns">
      <title>Name server</title>
 
      <para>As every microkernel, HelenOS has a "Name server" task with "well
      known" IPC address, that connects user task to any server just by the
      string service indentification.</para>
    </formalpara>
 
    <formalpara id="intro_ddi">
      <title>Device driver interface</title>
 
      <para>Device drivers use special syscalls to map physical memory areas
      into their address space, to map port regions (mostly ia32). Interrupts
      are delivered to the device driver task by the standard IPC
      means.</para>
    </formalpara>
  </section>
</chapter>

Rev 39	Rev 40
1	<?xml version="1.0" encoding="UTF-8"?>	1	<?xml version="1.0" encoding="UTF-8"?>
2	<chapter id="architecture">	2	<chapter id="architecture">
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	<title>Scheme</title>
9		9
10	<para><mediaobject id="arch1">	10	<para><mediaobject id="arch1">
11	<imageobject role="html">	11	<imageobject role="html">
12	<imagedata fileref="images/arch1.png" format="PNG" />	12	<imagedata fileref="images/arch1.png" format="PNG" />
13	</imageobject>	13	</imageobject>
14		14
15	<imageobject role="fop">	15	<imageobject role="fop">
16	<imagedata fileref="images.vector/arch1.svg" format="SVG" />	16	<imagedata fileref="images.vector/arch1.svg" format="SVG" />
17	</imageobject>	17	</imageobject>
18	</mediaobject></para>	18	</mediaobject></para>
19	</section>	19	</section>
20		20
21	<section>	21	<section>
22	<title>Kernel primitives</title>	22	<title>Kernel primitives</title>
23		23
24	<para><termdef><glossterm>Thread</glossterm> is the basic execution	24	<para><termdef><glossterm>Thread</glossterm> is the basic execution
25	primitive.</termdef></para>	25	primitive.</termdef></para>
26		26
27	<para><termdef><glossterm>Thread context</glossterm> represents state of	27	<para><termdef><glossterm>Thread context</glossterm> represents state of
28	the <emphasis>thread</emphasis>. Thread context is built of the context	28	the <emphasis>thread</emphasis>. Thread context is built of the context
29	registers contents, FPU state and the stack.</termdef></para>	29	registers contents, FPU state and the stack.</termdef></para>
30		30
31	<para><termdef> <glossterm>Task</glossterm> is a multi-purpose entity,	31	<para><termdef><glossterm>Task</glossterm> is a multi-purpose entity,
32	serving to <itemizedlist>	32	serving to incorporate set if its threads, provide common address space to its threads,
33	<listitem>incorporate set if its threads</listitem>	33	be an end-point in IPC.</termdef></para>
34		34
35	<listitem>provide common address space to its threads</listitem>	-
36		-
37	<listitem>be an end-point in IPC</listitem>	-
38	</itemizedlist> </termdef></para>	-
39		-
40	<para><termdef> <glossterm>Address space area</glossterm> is a mutually	35	<para><termdef><glossterm>Address space area</glossterm> is a mutually
41	disjunctive range of memory with the code, stack and data.	36	disjunctive range of memory with the code, stack and data.
42	</termdef></para>	37	</termdef></para>
43		38
44	<para><termdef> <glossterm>Address space</glossterm> is a aggregating	39	<para><termdef><glossterm>Address space</glossterm> is a aggregating
45	entity for address space areas, connecting them to the task.	40	entity for address space areas, connecting them to the task.
46	</termdef></para>	41	</termdef></para>
47	</section>	42	</section>
48		43
49	<section>	44	<section>
50	<title>Monolithic microkernel</title>	45	<title>Monolithic microkernel</title>
51		46
52	<para>Though HelenOS was initially planned as a microkernel, we were	47	<para>Though HelenOS was initially planned as a microkernel, we were
53	trying to avoid several issues, connected with microkernels, such as much	48	trying to avoid several issues, connected with microkernels, such as much
54	higher overhead during memory management and hardware operations. For this	49	higher overhead during memory management and hardware operations. For this
55	reason some of the subsystems, that are to be implemented as servers in	50	reason some of the subsystems, that are to be implemented as servers in
56	classic microkernel design, were implemented as a part of kernel, thus	51	classic microkernel design, were implemented as a part of kernel, thus
57	minimizing this overhead.</para>	52	minimizing this overhead.</para>
58		53
59	<formalpara>	54	<formalpara>
60	<title>Memory management</title>	55	<title>Memory management</title>
61		56
62	<para>Unlike the classic microkernel, HelenOS has all its memory	57	<para>HelenOS has all its memory
63	management functionality in the kernel, available to the memory	58	management functionality in the kernel, available to the memory
64	management server via the set of syscalls.</para>	59	management server via the set of syscalls.</para>
65	</formalpara>	60	</formalpara>
66		61
67	<formalpara>	62	<formalpara>
68	<title>Kernel device drivers</title>	63	<title>Kernel device drivers</title>
69		64
70	<para>HelenOS kernel has some of the very basic device drivers	65	<para>HelenOS kernel has some of the very basic device drivers
71	<itemizedlist>	66	<itemizedlist>
72	<listitem>	67	<listitem>
73	ACPI	68	ACPI
74	</listitem>	69	</listitem>
75		70
76	<listitem>	71	<listitem>
77	APIC	72	APIC
78	</listitem>	73	</listitem>
79		74
80	<listitem>	75	<listitem>
81	SMP configuration	76	SMP configuration
82	</listitem>	77	</listitem>
83		78
84	<listitem>	79	<listitem>
85	System clock	80	System clock
86	</listitem>	81	</listitem>
87		82
88	<listitem>	83	<listitem>
89	Interrupt controllers	84	Interrupt controllers
90	</listitem>	85	</listitem>
91		86
92	<listitem>	87	<listitem>
93	Console	88	Console and frame buffer
94	</listitem>	89	</listitem>
95		90
96	<listitem>	-
97	VESA & frame buffer	-
98	</listitem>	-
99	</itemizedlist></para>	91	</itemizedlist></para>
100	</formalpara>	92	</formalpara>
101	</section>	93	</section>
102		94
103	<section>	95	<section>
104	<title>IPC</title>	96	<title>IPC</title>
105		97
106	<para>HelenOS IPC is designed in analogy with telephone communication.	98	<para>HelenOS IPC is designed in analogy with telephone communication.
107	Each task has an <emphasis>answerbox</emphasis> and a set of	99	Each task has an <emphasis>answerbox</emphasis> and a set of
108	<emphasis>phones</emphasis> to call another tasks' answerboxes.</para>	100	<emphasis>phones</emphasis> to call another tasks' answerboxes.</para>
109		101
110	<para>Communication is possible after the connection is established, and	102	<para>Communication is possible after the connection is established, and
111	can be either <emphasis>asynchronious</emphasis> or	103	can be either <emphasis>asynchronious</emphasis> or
112	<emphasis>synchronious</emphasis>.</para>	104	<emphasis>synchronious</emphasis>.</para>
113	</section>	105	</section>
114		106
115	<section>	107	<section>
116	<title>Functionality model</title>	108	<title>Functionality model</title>
117		109
118	<para>As you know, microkernel design is very simple, just enough to	110	<para>As you know, microkernel design is very simple, just enough to
119	provide communication facility for tasks. Most of the OS functionality is	111	provide communication facility for tasks. Most of the OS functionality is
120	performed by server tasks, that are running in userspace. Thus most of the	112	performed by server tasks, that are running in userspace. Thus most of the
121	system calls in monolithic kernels, are the IPC calls on server tasks in	113	system calls in monolithic kernels, are the IPC calls on server tasks in
122	microkernels.</para>	114	microkernels.</para>
123		115
124	<para>Moreover, problems experience the device drivers. Running in the	116	<para>Moreover, problems experience the device drivers. Running in the
125	user space, device driver still needs to recieve interrupts and access	117	user space, device driver still needs to recieve interrupts and access
126	hardware directly.</para>	118	hardware directly.</para>
127		119
128	<para>This raises two major problems in microkernels: <orderedlist	120	<para>This raises two major problems in microkernels: <orderedlist
129	numeration="loweralpha">	121	numeration="loweralpha">
130	<listitem>	122	<listitem>
131	What is the recipient address of the server (e.g. "memory manager" or a specific device driver) ?	123	What is the recipient address of the server (e.g. "memory manager" or a specific device driver) ?
132	</listitem>	124	</listitem>
133		125
134	<listitem>	126	<listitem>
135	How this server task is going to access hardware or kernel while running in the user mode?	127	How this server task is going to access hardware or kernel while running in the user mode?
136	</listitem>	128	</listitem>
137	</orderedlist></para>	129	</orderedlist></para>
138		130
139	<formalpara id="intro_ns">	131	<formalpara id="intro_ns">
140	<title>Name server</title>	132	<title>Name server</title>
141		133
142	<para>As every microkernel, HelenOS has a "Name server" task with "well	134	<para>As every microkernel, HelenOS has a "Name server" task with "well
143	known" IPC address, that connects user task to any server just by the	135	known" IPC address, that connects user task to any server just by the
144	string service indentification.</para>	136	string service indentification.</para>
145	</formalpara>	137	</formalpara>
146		138
147	<formalpara id="intro_ddi">	139	<formalpara id="intro_ddi">
148	<title>Device driver interface</title>	140	<title>Device driver interface</title>
149		141
150	<para>Device drivers use special syscalls to map physical memory areas	142	<para>Device drivers use special syscalls to map physical memory areas
151	into their address space, to map port regions (mostly ia32). Interrupts	143	into their address space, to map port regions (mostly ia32). Interrupts
152	are delivered to the device driver task by the standard IPC	144	are delivered to the device driver task by the standard IPC
153	means.</para>	145	means.</para>
154	</formalpara>	146	</formalpara>
155	</section>	147	</section>
156	</chapter>	148	</chapter>

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