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doc/docbook/development/development.dbk
$Id: development.dbk,v 1.13 2003/11/02 10:23:59 cbothamy Exp $

This is the top level file for the Bochs Developers Manual.
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook V4.1//EN" [

<!-- include definitions that are common to all bochs documentation -->
<!ENTITY % bochsdefs SYSTEM "../include/defs.sgm">
%bochsdefs;

]>
<book>
<bookinfo>
   <title>Bochs Developers Guide</title>
   <authorgroup>
   <author><firstname>Kevin</firstname><surname>Lawton</surname></author>
   <author><firstname>Bryce</firstname><surname>Denney</surname></author>
   <author><firstname>Christophe</firstname><surname>Bothamy</surname></author>
   <editor><firstname>Michael</firstname><surname>Calabrese</surname></editor>
   </authorgroup>
</bookinfo>

<!-- *************************************************************** -->
<chapter id="resources"><title>Resources for developers</title>
<para>
The development guide describes resources that are intended for developers
in particular.  Many Bochs resources are also covered in the User Guide,
including compile instructions, bochsrc options, how to find the mailing
lists, etc.
</para>


<section><title>Setting up CVS write access</title>
<para>
If you are an official SourceForge developer, then you can use CVS with write
access.  The CVS contains the most recent copy of the source code, and with
write access you can upload any changes you make to the CVS server for others
to use.  A few extra steps are required the first time you use CVS write
access.
</para>

<section><title>Install ssh and cvs</title>
<para>
First you need to install both cvs (Concurrent Version System) and ssh (Secure
Shell).  These are already installed on many UNIX systems and also Cygwin
(win32 platform).  If not, you can install binaries or compile cvs and ssh
yourself.  The links below should help you get going.
</para>
<itemizedlist>
<listitem> <para> CVS software and instructions are available at <ulink url="http://www.cvshome.org">www.cvshome.org</ulink>. </para> </listitem>
<listitem> <para> A free version of secure shell called OpenSSH is at <ulink url="http://www.openssh.org">www.openssh.org</ulink>. </para> </listitem>
<listitem> <para> OpenSSH requires a library called OpenSSL from <ulink url="http://www.openssl.org">www.openssl.org</ulink>.  Be sure to install OpenSSL before trying to compile OpenSSH. </para> </listitem>
</itemizedlist>
</section> 

<section><title>ssh to cvs.sf.net</title>
<para>
Next, you need to use secure shell to connect to cvs.sf.net.  This step is a
little strange, because you can't actually log in and get a shell prompt.  All
that will happen, when you get the username and password right, is that it
will create a home directory on that machine for you.  That's it!  If you try
it again, it will say "This is a restricted Shell Account.  You cannot execute
anything here."   At this point, you've succeeded and you never have to do
this step again, ever.

<screen>
  ssh <replaceable>sfusername</replaceable>@cvs.sf.net
</screen>
</para>

<para>
Replace <replaceable>sfusername</replaceable> with your Source Forge username,
of course.  The first time, you will probably get a message like 
<screen>
The authenticity of host 'cvs.sf.net' can't be established.
Are you sure you want to continue?</screen>

Just type yes.  When it asks for a password, be sure to type your source 
forge password.  If you have trouble logging in, be sure to use your SOURCE
FORGE username and password in the ssh line, which isn't necessarily the same
as your local username and password.  Add the "-v" option to ssh to see more
information about what is failing.  If you have ssh version 2, it is possible
that you might need to add "-1" to the ssh command to force it to use the
version 1 protocol.  </para> </section> 

<section><title>Set CVS_RSH environment variable to ssh</title>
<para>
Every time you connect to the Source Forge CVS server (including cvs update,
stat, commit, etc.), you must set the CVS_RSH environment variable to ssh.  So
just take the time now to add one of these lines to your .bashrc/.cshrc, so
that the CVS_RSH setting will be there every time you log in.
</para>

<screen>
  export CVS_RSH=ssh           (bash syntax)
  setenv CVS_RSH ssh           (csh syntax)
</screen>
</section> <!--end of "Set environment variable"-->

<section><title>cvs checkout</title>
<para>
Finally, you should be able to do the checkout!  If you already have a bochs
subdirectory directory, move it out of the way because the checkout will
overwrite it.
</para>

<screen>
  export CVSROOT=":ext:<replaceable>sfusername</replaceable>@cvs.bochs.sourceforge.net:/cvsroot/bochs"
  cvs -z3 checkout bochs
  <replaceable>sfusername</replaceable>@cvs.sf.net's password:        <replaceable><--type your password</replaceable>
</screen>

<para>
In the CVSROOT variable, replace <replaceable>sfusername</replaceable> with your SF username.  There's
no need to add CVSROOT to your rc files because CVS will remember it
after the checkout.  The -z3 (optional) just adds some compression to make 
the checkout go faster.  Once all the files have been downloaded, you will
have a bochs directory which is checked out with write access!
</para>
</section> <!-- end cvs checkout -->

</section> <!-- end setting up cvs write access -->

<section id="using-cvs-write-access"><title>Using CVS write access</title>

<section><title>Checking in files</title>
<para>
Once you have a bochs directory with cvs write access, you can compile the
files, edit them, test them, etc.  See the documentation section, "Tracking
the source code with CVS" for more info on CVS, in the User Manual.
(FIXME: add cross reference) But what's new and different is that you can now
do cvs commits.  When a file is all fixed and ready to share with the rest of
the world, you run a commit command to upload your version to the server.
First, it's good to do a cvs update to make sure nobody else has changed it
since you downloaded it last.
</para>

<screen>
  $ cvs update file.cc
  <replaceable>sfusername</replaceable>@cvs.sf.net's password:        <replaceable><--type your password</replaceable>
  $ cvs commit file.cc
  <replaceable>sfusername</replaceable>@cvs.sf.net's password:        <replaceable><--type your password</replaceable>
  [editor opens. type log message, save, and exit.]
</screen>

<para>
When CVS starts an editor, The default is usually vi.  If you want a different
editor, set the EDITOR environment variable to the name of your preferred
editor.  When you're done, just save the file and quit the editor.  Unless
there's some problem, you will see a message that says what the new revision
number for the file is, and then "done".  If while you're editing the log
message, you decide that you don't want to commit after all, don't save the
file.  Quit the editor, and when it asks where the log message went, tell it
to abort.
</para>

<para>
Here is an example of a successful checkin:

<screen>
  $ cvs commit misc.txt
  <replaceable>sfusername</replaceable>@cvs.sf.net's password:        <replaceable><--type your password</replaceable>
  [edit log msg]
  Checking in misc.txt;
  /cvsroot/bochs/bochs/doc/docbook/misc.txt,v  <--  misc.txt
  new revision: 1.6; previous revision: 1.5
  done
</screen>

And here is an aborted one:

<screen>
  $ cvs commit misc.txt
  <replaceable>sfusername</replaceable>@cvs.sf.net's password:        <replaceable><--type your password</replaceable>
  [quit editor without saving]
  Log message unchanged or not specified
  a)bort, c)ontinue, e)dit, !)reuse this message unchanged for remaining dirs
  Action: a
  cvs [commit aborted]: aborted by user
</screen>

</para>
</section> <!--end of "Checking in Files" -->

</section> <!--end of "Using CVS write access" -->

      <section id="trackers"><title>SourceForge bug, feature, and patch trackers</title>
         <para>
	 &FIXME;
         </para>
      </section>

<section id="other"><title>Ideas for other sections</title>
<para>
<screen>
Ideas:
- how to browse code with cvsweb
- how to find an identifier, variable, or specific text in the code
- write access CVS (must be an official developer on SF)
- how to make patches with CVS
</screen>
</para>
</section>

</chapter>

 <chapter id="about-the-code"><title>About the code</title>

<section><title>How to add keymapping in a GUI client</title>
<para>
Christophe Bothamy, wrote the keymapping code for Bochs, provided these
instructions to help developers to add keymapping to a GUI.
</para>

<screen>
Bochs creates a bx_keymap_c object named bx_keymap.
This object allows you to :
  - load the configuration specified keymap file
  - get the translated BX_KEY_* from your GUI key

You have to provide a translation function from string to your Bit32u key
constant. Casting will be necessary if your key constants are not Bit32u typed.
The function must be "static Bit32u (*)(const char *)" typed, and must return
BX_KEYMAP_UNKNOWN if it can not translate the parameter string.

What you have to do is :
  - call once "void loadKeymap(Bit32u (*)(const char*))", 
    providing your translation function, to load the keymap
  - call "Bit32u getBXKey(Bit32u)" that returns the BX_KEY_*
    constant, for each key you want to map.

The file gui/x.cc implements this architecture, so you can refer to it
as an example.
</screen>

</section>

    <section id="directory-structure"><title>Directory Structure</title>
      <para>
      &FIXME;
      cpu directory does this, iodev does that, gui does that
      </para>
    </section>

     <section id="configure-scripting"><title>Configure Scripting</title>
      <para>
      &FIXME;
      configure script, makefiles, header files
      </para>
     </section>

      <section id="logfunctions"><title>Log Functions</title>
      <para>
      &FIXME;
      log functions: what is a panic, what is an error, etc.
      </para>
      </section>

      <section id="emulator-objects"><title>Emulator Objects</title>
       <para>
      &FIXME;
      objects that do all the work (cpu, mem)
      </para>
      </section>

      <section id="timers"><title>timers</title>
      <para>
      &FIXME;
      </para>
      </section>

<section id="sb16-emulation-basics"> <!-- start of SB16 section-->

<title>Sound Blaster 16 Emulation</title>
<para>
Sound Blaster 16 (SB16) emulation for Bochs was written and donated by
Josef Drexler, who has a
<ulink url="http://publish.uwo.ca/~jdrexler/bochs/">web page</ulink> on the topic.
  The entire set of his SB16 patches have been integrated into
Bochs, however, so you can find everything you need here.
</para>

<para>
SB16 Emulation has been tested with several soundcards and versions of Linux.  Please give
Josef <ulink url="mailto:jdrexler@julian.uwo.ca">feedback</ulink> on 
whether is does or doesn't work on your combination of software and hardware.
</para>

<section><title>How well does it work?</title>
<para>
Right now, MPU401 emulation is next to perfect. It supports UART
and SBMIDI mode, because the SB16's MPU401 ports can't do anything else as well.
</para>

<para>
The digital audio basically works, but the emulation is too slow for fluent
output unless the application doesn't do much in the background (or the
foreground, really). The sound tends to looping or crackle on slower
computer, but the emulation appears to be correct. Even a MOD
player works, although only for lower sampling speeds.
</para>
<para>
Also, the MIDI data running through the MPU401 ports can be written
into a SMF, that is the standard midi file. The wave output
can be written into a VOC file, which has a format defined by
Creative Labs. This file format can be converted to WAV by
sox for example.
</para>
</section>

<section><title>Output to a sound card</title>

<para>
Output is supported on Linux and Windows 95 at the moment.
On Linux, the output goes to any file or device. If you have a
wavetable synthesizer, midi can go to /dev/midi00, otherwise you may need
a midi interpreter. For example, the midid program from the
DosEmu project would work. Wave output should go to /dev/dsp.
These devices are assumed to be OSS devices, if they're not
some of the ioctl's might fail.
On Windows, midi and output goes to the midi mapper and the wave mapper,
respectively. A future version might have selectable output devices.
</para>
</section>

<section><title>Installation on Linux</title>

<para>
<emphasis>Prerequisites:</emphasis>
</para>

<para>
A wavetable synthesizer on /dev/midi00 and a working /dev/dsp if you want real time music and sound, otherwise output to midi and wave files is also possible. 
Optionally, you can use a software midi interpreter, such as the midid program from the DosEmu project instead of /dev/midi00. 
</para>
</section>

<section><title>Configuring bochs</title>

<para>
There are a few values in config.h that are relevant to the sound functions.
Edit config.h after running configure, but before compiling.
</para>

<para>
BX_USE_SB16_SMF should be 1 unless you intend to have several sound cards
running at the same time.
</para>

<para>
BX_USE_SOUND_VIRTUAL can be 0 or 1, and determines whether the output class
uses virtual functions or not. The former is more versatile and allows to
select the class at runtime (not supported at the moment), while the latter
is slightly faster.
</para>

<para>
BX_SOUND_OUTPUT_C is the name of the class used for output.  The default is
to have no output functions, so you need to change this if you want any sound.
The following are supported at the moment:
</para>

<programlisting>
        bx_sound_linux_c    for output to /dev/dsp and /dev/midi00 on Linux
                            (and maybe other OSes that use the OSS driver)
        bx_sound_windows_c  for output to the midi and wave mapper of
                            Windows 3.1 and higher.
        bx_sound_output_c   for no output at all.
</programlisting>

<para>
Setup the SB16 emulation in your .bochsrc, according to instructions
in that file.
</para>
</section>

<section><title>Runtime configuration</title>

<para>
The source for the SB16CTRL program that is used to modify
the runtime behaviour of the SB16 emulator is included in
misc/sb16. You can compile it or download the
<ulink url="http://publish.uwo.ca/~jdrexler/bochs/">executable</ulink>.
</para>

<para>
See the section "Sound Blaster 16 Emulation" in the user documentation for
information about the commands of SB16CTRL.
</para>
</section>

<section><title>Features planned for the future</title>
<itemizedlist>
<listitem><para>Ports to more OS's, but I can't do this myself</para></listitem>
<listitem><para>Finishing the OPL3 FM emulation by translating the music to midi data</para></listitem>
</itemizedlist>
</section>

<section>
<title>Description of the sound output classes</title>

<para>
This file is intended for programmers who would like to port the sound
output routines to their platform. It gives a short outline what services
have to be provided.
</para>
<para>
You should also have a look at the exisiting files, <emphasis>SOUNDLNX.CC</emphasis>
for Linux and <emphasis>SOUNDWIN.CC</emphasis> for Windows and their respective
header files to get an idea about how these things really work.
</para>
</section>

<section><title>Files</title>

<para>
The main include file is <emphasis>bochs.h</emphasis>. It has all definitions 
for the system-independent functions that the SB16 emulation uses, which
are defined in <emphasis>sb16.h</emphasis>.
</para>

<para>
Additionally, every output driver will have an include file, which
should be included at the end of sb16.h to allow the emulator
to use that driver.
</para>

<para>
To actually make the emulator use any specific driver, 
<emphasis>BX_SOUND_OUTPUT_C</emphasis> has to be set to the name of the respective
output class.
</para>

<para>
Note that if your class contains any system-specific statements,
include-files and so on, you should enclose both the include-file and
the CC-file in an <emphasis>#if defined</emphasis> (OS-define) construct.
Also don't forget to add your file to the object list in
iodev/Makefile and iodev/Makefile.in.
</para>
</section>

<section><title>Classes</title>

<para>
The following classes are involved with the SB16 emulation:
</para>
<itemizedlist>
<listitem><para>
<emphasis>bx_sb16_c</emphasis> is the class containing the emulator itself, that
is the part acting on port accesses by the application, handling the
DMA transfers and so on. It also prepares the data for the output
classes.
</para></listitem>

<listitem><para>
<emphasis>bx_sound_output_c</emphasis> is the base output class. It has all
the methods used by the emulator, but only as stubs and does not
actually produce any output. These methods are then called by
the emulator whenever output is necessary.
</para></listitem>

<listitem><para>
<emphasis>bx_sound_OS_c</emphasis> is derived from 
<emphasis>bx_sound_output_c</emphasis>. It contains the code to generate 
output for the <emphasis>OS</emphasis> operating system. 
It is necessary to override all
the methods defined in the base class, unless virtual functions
are used. Note that this should remain an option, so try to
override all methods, even if only as stubs. They should be
declared <emphasis>virtual</emphasis> if and only if <emphasis>BX_USE_SOUND_VIRTUAL</emphasis>
is defined, just as in the examples. 
The constructor should call the inherited constructor
as usual, even though the current constructor does not do
anything yet.
</para></listitem>
</itemizedlist>
</section>


<section><title>Methods</title>
<para>
The following are the methods that the output class has to override.
All but constructor and destructor have to return either
<emphasis>BX_SOUND_OUTPUT_OK</emphasis> <emphasis>(0)</emphasis> if the function was successful, 
or <emphasis>BX_SOUND_OUTPUT_ERR</emphasis> <emphasis>(1)</emphasis> if not. If any of the initialization
functions fail, output to that device is disabled until the emulator is restarted.
</para>
</section>

<section><title>bx_sound_OS_c(bx_sb16_c*sb16)</title>

<para>
The emulator instantiates the class at the initialization of Bochs.
</para>

<para>
Description of the parameter:
</para>

<itemizedlist>
<listitem><para>
<emphasis>sb16</emphasis> is a pointer to the emulator class. 
This pointer can then be used to access for example the <emphasis>writelog</emphasis> function to generate
sound-related log messages. Apart from that, no access to the emulator
should be necessary.
</para></listitem>

<listitem><para>
The constructor should <emphasis>not</emphasis> allocate the output devices. 
This shouldn't be done until the actual output occurs; in either 
<emphasis>initmidioutput()</emphasis> or <emphasis>initwaveoutput()</emphasis>.
Otherwise it would be impossible to have two copies of Bochs running 
concurrently (if anybody ever wants to do this).
</para></listitem>
</itemizedlist>
</section>

<section><title>~bx_sound_OS_c()</title>

<para>
The instance is destroyed just before Bochs ends.
</para>
</section>

<section><title>int openmidioutput(char *device)</title>

<itemizedlist>
<listitem><para>
<emphasis>openmidioutput()</emphasis> is called when the first midi output starts.
It is only called if the midi output mode is 1 (midimode 1). It should
prepare the given MIDI hardware for receiving midi commands.
</para></listitem>

<listitem><para>
<emphasis>openmidioutput()</emphasis> will always be called before <emphasis>openwaveoutput()</emphasis>,
and <emphasis>closemidioutput()</emphasis>will always be called before <emphasis>closewaveoutput()</emphasis>, but not in all cases will both functions be called.
</para></listitem>
</itemizedlist>
</section>

<section>
<title>Description of the parameters:</title>

<itemizedlist>

<listitem><para>
<emphasis>device</emphasis> is a system-dependent variable.
It contains the value of the <emphasis>MIDI=device</emphasis> configuration option.
</para></listitem>

<listitem><para>
Note that only one midi output device will be used at any one time.
<emphasis>device</emphasis>
may not have the same value throughout one session, but it will be closed
before it is changed.
</para></listitem>
</itemizedlist>
</section>

<section><title>int midiready()</title>

<para>
<emphasis>midiready()</emphasis> is called whenever the applications asks if the
midi queue can accept more data. 
</para>

<para>
Return values:
</para>

<itemizedlist>
<listitem><para>
<emphasis>BX_SOUND_OUTPUT_OK</emphasis> if the midi output device is ready.  
</para></listitem>

<listitem><para>
<emphasis>BX_SOUND_OUTPUT_ERR</emphasis> if it isn't ready.  
</para></listitem>
</itemizedlist>

<para>
<emphasis>Note: </emphasis><emphasis>midiready()</emphasis> will be called a few times
<emphasis>before</emphasis> the device is opened. If this is the case, it should
always report that it is ready, otherwise the application (not Bochs)
will hang.
</para>
</section>

<section><title>int sendmidicommand(int delta, int command, int length, Bit8u data[])</title>

<para>
<emphasis>sendmidicommand()</emphasis>is called whenever a complete midi command has
been written to the emulator. It should then send the given midi command to the midi hardware.
It will only be called after the midi output has been opened. Note that
if at all possible it should not wait for the completion of the command
and instead indicate that the device is not ready during the execution
of the command. This is to avoid delays in the program while it is
generating midi output.
</para>

<para>
Description of the parameters:
</para>

<itemizedlist>
<listitem><para>
<emphasis>delta</emphasis> is the number of delta ticks that
have passed since the last command has been issued. It is always zero for
the first command. There are 24 delta ticks per quarter, and 120 quarters
per minute, thus 48 delta ticks per second.
</para></listitem>

<listitem><para>
<emphasis>command</emphasis> is the midi command byte (sometimes
called status byte), in the usual range of 0x80..0xff. For more information
please see the midi standard specification.
</para></listitem>

<listitem><para>
<emphasis>length</emphasis> is the number of data bytes that
are contained in the data structure. This does <emphasis>not</emphasis> include the status
byte which is not replicated in the data array. It can only be greater
than 3 for SysEx messages (commands <emphasis>0xF0</emphasis> and <emphasis>0xF7</emphasis>)
</para></listitem>

<listitem><para>
<emphasis>data[]</emphasis> is the array of these data bytes,
in the order they have in the standard MIDI specification.
Note, it might be <emphasis>NULL</emphasis> if length==0.
</para></listitem>
</itemizedlist>
</section>


<section><title>int closemidioutput()</title>

<para>
<emphasis>closemidioutput()</emphasis> is called before shutting down Bochs or 
when the
emulator gets the <emphasis>stop_output</emphasis> command through the emulator port.
After this, no more output will be necessary until <emphasis>openmidioutput()</emphasis>
is called again, but <emphasis>midiready()</emphasis> might still be called. It should do the following:
</para>

<itemizedlist>
<listitem><para>
Wait for all remaining messages to be completed
</para></listitem>
<listitem><para>
Reset and close the midi output device
</para></listitem>
</itemizedlist>
</section>


<section><title>int openwaveoutput(char *device)</title>

<para>
<emphasis>openwaveoutput()</emphasis> is called when the first wave output occurs,
and only if the selected wavemode is 1. It should do the following:
</para>

<itemizedlist>
<listitem><para>
Open the given device, and prepare it for wave output
</para></listitem>
</itemizedlist>
<para>
<emphasis>or</emphasis>
</para>
<itemizedlist>
<listitem><para>
Store the device name so that the device can be opened in <emphasis>startplayback()</emphasis>.
</para></listitem>
</itemizedlist>

<para>
<emphasis>openmidioutput()</emphasis> will always be called before <emphasis>openwaveoutput()</emphasis>,
and <emphasis>closemidioutput()</emphasis>will always be called before <emphasis>closewaveoutput()</emphasis>, but not in all cases will both functions be called.
</para>

<para>
<emphasis>openwaveoutput()</emphasis> will typically be called once, whereas
<emphasis>startplayback()</emphasis> is called for every new DMA transfer to the SB16 emulation. If feasible,
it could be useful to open and/or lock the output device in
<emphasis>startplayback()</emphasis> as opposed to <emphasis>openwaveoutput()</emphasis>
to ensure that it can be used by other applications while Bochs doesn't
need it.
</para>

<para>
However, many older applications don't use the auto-init DMA
mode, which means that they start a new DMA transfer for every single
block of output, which means usually for every 2048 bytes or so.
Unfortunately there is no way of knowing whether the application will
restart an expired DMA transfer soon, so that in these cases the
<emphasis>startwaveplayback</emphasis> function will be called very often, and it
isn't a good idea to have it reopen the device every time.
</para>

<para>The buffer when writing to the device should not be overly large.
Usually about four buffers of 4096 bytes produce best results. Smaller
buffers could mean too much overhead, while larger buffers contribute
to the fact that the actual output will always be late when the application
tries to synchronize it with for example graphics.
</para>

<para>The parameters are the following: </para>

<itemizedlist>
<listitem><para>
<emphasis>device</emphasis> is the wave device selected by
the user. It is strictly system-dependent. The value is that of the
<emphasis>WAVE=device</emphasis>
configuration option.
</para></listitem>
</itemizedlist>

<para>
Note that only one wave output device will be used at any one time.
<emphasis>device</emphasis> may not have the same value throughout one session, but it will be closed
before it is changed.
</para>
</section>

<section>
<title>int startwaveplayback(int frequency, int bits, int stereo, int format)</title>

<para>
This function is called whenever the application starts a new DMA transfer.  It should do the following:
</para>

<itemizedlist>
<listitem><para>
Open the wave output device, unless <emphasis>openwaveoutput()</emphasis> did that
already
</para></listitem>

<listitem><para>
Prepare the device for data and set the device parameters to those given
in the function call
</para></listitem>
</itemizedlist>

<para>
The parameters are the following:
</para>

<itemizedlist>
<listitem><para>
<emphasis>frequency</emphasis> is the desired frequency of the
output. Because of the capabities of the SB16, it can have any value between
5000 and 44,100.
</para></listitem>

<listitem><para>
<emphasis>bits</emphasis> is either 8 or 16, denoting the resolution
of one sample.
</para></listitem>

<listitem><para>
<emphasis>stereo</emphasis> is either 1 for stereo output, or 0 for mono output.
</para></listitem>

<listitem><para>
<emphasis>format</emphasis> is a bit-coded value (see below).
</para></listitem>
</itemizedlist>

<para>
<table>   
<title>format bits</title>
<tgroup cols="2">
<thead>
<row>
<entry>Bit number</entry>
<entry>Meaning</entry>
</row>
</thead>
<tbody>
<row> <entry> 0 (LSB)  </entry><entry><para> 0: unsigned data </para><para>
                                            1: signed data </para></entry> </row>
<row> <entry> 1..6     </entry><entry> Type of codec (see below) </entry> </row>
<row> <entry> 7        </entry><entry><para> 0: no reference byte </para><para>
                                             1: with reference byte </para></entry> </row>
<row> <entry> 8..x     </entry><entry> reserved (0) </entry> </row>
</tbody>
</tgroup>
</table>

<table>   
<title>codecs</title>
<tgroup cols="2">
<thead>
<row>
<entry>Value</entry>
<entry>Meaning</entry>
</row>
</thead>
<tbody>
<row> <entry> 0 </entry><entry> PCM (raw data) </entry> </row>
<row> <entry> 1 </entry><entry> reserved </entry> </row>
<row> <entry> 2 </entry><entry> 2-bit ADPCM (Creative Labs format) </entry> </row>
<row> <entry> 3 </entry><entry> 2.4-bit (3-bit) ADPCM (Creative Labs format) </entry> </row>
<row> <entry> 4 </entry><entry> 4-bit ADPCM (Creative Labs format) </entry> </row>
</tbody>
</tgroup>
</table>
</para>
<para>
Other codecs are not supported by the SB hardware. In fact, most applications will
translate their data into raw data, so that in most cases the codec will be zero.
</para>
<para>
The number of bytes per sample can be calculated from this as (bits / 8) * (stereo + 1).
</para>
</section>


<section>
<title>int waveready()</title>

<para>
This is called whenever the emulator has another output buffer ready
and would like to pass it to the output class. This happens every
<emphasis>BX_SOUND_OUTPUT_WAVEPACKETSIZE</emphasis> bytes, or whenever a DMA transfer
is done or aborted.
</para>

<para>
It should return whether the output device is ready for another buffer
of <emphasis>BX_SOUND_OUTPUT_WAVEPACKETSIZE</emphasis> bytes. 
If <emphasis>BX_SOUND_OUTPUT_ERR</emphasis>
is returned, the emulator waits about 1/(frequency * bytes per sample) seconds 
and then asks again. The DMA transfer is stalled during that time, but
the application keeps running, until the output device becomes ready.
</para>

<para>
As opposed to <emphasis>midiready(), waveready()</emphasis> will <emphasis>not</emphasis> be
called unless the device is open.
</para>
</section>

<section>
<title>int sendwavepacket(int length, Bit8u data[])</title>

<para>
This function is called whenever a data packet of at most <emphasis>BX_SB16_WAVEPACKETSIZE</emphasis>
is ready at the SB16 emulator. It should then do the following:
</para>

<itemizedlist>
<listitem><para>
Send this wave packet to the wave hardware
</para></listitem>
</itemizedlist>

<para>
This function <emphasis>has</emphasis> to be synchronous, meaning that it <emphasis>has</emphasis>
to return immediately, and <emphasis>not</emphasis> wait until the output is done. Also,
this function might be called before the previous output is done. If your
hardware can't append the new output to the old one, you will have to implement
this yourself, or the output will be very chunky, with as much silence
between the blocks as the blocks take to play. This is not what you want.
Instead, <emphasis>waveready()</emphasis> should return <emphasis>BX_SOUND_OUTPUT_ERR</emphasis>
until the device accepts another block of data.
</para>

<para>
Parameters:
</para>

<itemizedlist>
<listitem><para>
<emphasis>length</emphasis> is the number of data bytes in
the data stream. It will never be larger than <emphasis>BX_SB16_WAVEPACKETSIZE</emphasis>.
</para></listitem>

<listitem><para>
<emphasis>data</emphasis> is the array of data bytes.
</para></listitem>
</itemizedlist>

<para>
The order of bytes in the data stream is the same as that in the Wave file format:

<table>   
<title>wave output types</title>
<tgroup cols="2">
<thead>
<row>
<entry>Output type</entry>
<entry>Sequence of data bytes</entry>
</row>
</thead>
<tbody>
<row> <entry> 8 bit mono </entry><entry> Sample 1; Sample 2; Sample 3; etc. </entry> </row>
<row> <entry> 8 bit stereo </entry><entry> Sample 1, Channel 0; Sample 1, Channel 1; Sample 2, Channel 0; Sample 2, Channel 1; etc. </entry> </row>
<row> <entry> 16 bit mono </entry><entry> Sample 1, LSB; Sample 1, MSB; Sample 2, LSB; Sample 2, MSB; etc. </entry> </row>
<row> <entry> 16 bit stereo </entry><entry> Sample 1, LSB, Channel 0; Sample 1, MSB, Channel 0; Sample 1, LSB, Channel 1; Sample 1, MSB, Channel 1; etc. </entry> </row>
</tbody>
</tgroup>
</table>
</para>

<para>
Typically 8 bit data will be unsigned with values from 0 to 255, and
16 bit data will be signed with values from -32768 to 32767, although the
SB16 is not limited to this. For further information on the codecs and
the use of reference bytes please refer to the Creative Labs Sound Blaster
Programmer's Manual, which can be downloaded from the Creative Labs web
site.
</para>
</section>

<section><title>int stopwaveplayback()</title>

<para>
This function is called at the end of a DMA transfer. It should do the following:
</para>

<itemizedlist>
<listitem><para>
Close the output device if it was opened by <emphasis>startwaveplayback()</emphasis>.
and it's not going to be opened soon. Which is almost impossible to tell.
</para></listitem>
</itemizedlist>
</section>

<section><title>int closewaveoutput()</title>

<para>
This function is called just before Bochs exits. It should do the following:
</para>

<itemizedlist>
<listitem><para>
 Close the output device, if this hasn't been done by <emphasis>stopwaveplayback()</emphasis>.
</para></listitem>
</itemizedlist>

<para>
Typically, <emphasis>stopwaveplayback()</emphasis> will be called several times, whenever
a DMA transfer is done, where <emphasis>closewaveoutput()</emphasis> will only be called
once. However, in the future it might be possible that <emphasis>openwaveoutput()</emphasis>
is called again, for example if the user chose to switch devices while
Bochs was running. This is not supported at the moment, but might be in
the future.
</para>
</section>

</section> <!-- end of SB16 section-->

<section id="harddisk-redologs"><title>Harddisk Images based on redologs</title>
<para>
This section describes how the three new disk images "undoable", "growing", and "volatile" are 
implemented in Bochs 2.1 :
</para>
<itemizedlist>
<listitem><para>
undoable -> flat file, plus growing, commitable, rollbackable redolog file
</para></listitem>
<listitem><para>
growing  -> growing files, all previously unwritten sectors go to the end of file
</para></listitem>
<listitem><para>
volatile -> flat file, plus hidden growing redolog
</para></listitem>
</itemizedlist>

<para>
</para>

<section>
<title>
        Description
</title>
<para>
The idea behind volatile and undoable disk images 
is to have a flat file, associated with one redolog file. 
</para>
<para>
Reading a sector is done from the redolog file if it contains 
the sector, or from the flat file otherwise. 
</para>
<para>
Sectors written go to the redolog,
so flat files are opened in read only mode in this configuration.
</para>
<para>
The redolog is designed in a way so it starts as a small file
and grows with every new sectors written to it. Previously written
sectors are done in place. Redolog files can not shrink.
</para>
<para>
The redolog is a growing file that can be created on the fly.
</para>
<para>
Now, it turns out that if you only use a redolog without any 
flat file, you get a "growing" disk image.
</para>
<para>
So "undoable", "volatile" and "growing" harddisk images classes
are implemented on top of a redolog class.
</para>
</section>

<section>
<title>
        How redologs works ?
</title>

<para>
At the start of a redolog file, there is a header, so Bochs can check whether
a file is consistent. 
This header could also be checked when we implement
automatic type and size detection.
</para>
<para>
The generic part of the header contains values like type of image, and
spec version number.
</para>
<para>
The header also has a specific part.
For redologs, the number
of entries of the catalog, the extent, bitmap and disk size are stored.
</para>

<para>
In a redolog, the disk image is divided in a number of equal size "extents".
Each extent is a collection of successive 512-bytes sectors of the disk image,
preceeded by a n*512bytes bitmap. 
</para>

<para>
the n*512bytes bitmap defines the presence (data has been written to it)
of a specific sector in the extent, one bit for each sector.
Therefore with a 512bytes bitmap, each extent can hold up to 4k blocks
</para>

<para>
Typically the catalog can have 256k entries.
With a 256k entries catalog and 512bytes bitmaps, the redolog can hold up to 512GiB
</para>

<note>
<para>
All data is stored on images as little-endian values
</para>
</note>
<section>
<title>
        Header
</title>
<para>
At the start of a redolog file, there is a header. This header is designed
to be reusable by other disk image types.
</para>
<para>
The header length is 512 bytes. It contains :
<table>   
<title>Generic header description</title>
<tgroup cols="5">
<thead>
<row>
<entry>Start position in bytes</entry>
<entry>Length in bytes</entry>
<entry>Data type</entry>
<entry>Description</entry>
<entry>Possible values</entry>
</row>
</thead>
<tbody>
<row> <entry> 0 </entry> <entry> 32 </entry> <entry> string </entry> <entry> magical value </entry> <entry> Bochs Virtual HD Image </entry> </row>
<row> <entry> 32 </entry> <entry> 16 </entry> <entry> string </entry> <entry> type of file </entry> <entry> Redolog </entry> </row>
<row> <entry> 48 </entry> <entry> 16 </entry> <entry> string </entry> <entry> subtype of file </entry> <entry> Undoable, Volatile, Growing </entry> </row>
<row> <entry> 64 </entry> <entry> 4 </entry> <entry> Bit32u </entry> <entry> version of used specification </entry> <entry> 0x00010000 </entry> </row>
<row> <entry> 68 </entry> <entry> 4 </entry> <entry> Bit32u </entry> <entry> header size </entry> <entry> 512 </entry> </row>
</tbody>
</tgroup>
</table>
<table>   
<title>Redolog specific header description</title>
<tgroup cols="5">
<thead>
<row>
<entry>Start position in bytes</entry>
<entry>Length in bytes</entry>
<entry>Data type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row> <entry> 72 </entry> <entry> 4 </entry> <entry> Bit32u </entry> <entry> number of entries in the catalog </entry> </row>
<row> <entry> 76 </entry> <entry> 4 </entry> <entry> Bit32u </entry> <entry> bitmap size in bytes </entry> </row>
<row> <entry> 80 </entry> <entry> 4 </entry> <entry> Bit32u </entry> <entry> extent size in bytes</entry> </row>
<row> <entry> 84 </entry> <entry> 8 </entry> <entry> Bit64u </entry> <entry> disk size in bytes </entry> </row>
</tbody>
</tgroup>
</table>
</para>
</section>
<section>
<title>
        Catalog
</title>
<para>
Immediately following the header, there is a catalog containing
the position number (in extents) where each extent is located in the file.
</para>
<para>
Each position is a Bit32u entity.
</para>

</section>
<section>
<title>
        Extent
</title>
<para>
	 &FIXME;
</para>
</section>
</section>

<section>
<title>Parameters
</title>
<para>
The following tables shows what paremeters are used when creating redologs or creating égrowing" images :
<table>   
<title>
        How number of entries in the catalog and number of blocks by extents are computed
</title>
<tgroup cols="5">
<thead>
<row>
<entry>Catalog entries</entry> <entry>Catalog size(KiB)</entry> <entry>Bitmap size (B)</entry> <entry>Extent size (KiB)</entry> <entry>Disk Max Size</entry>
</row>
</thead>

<tbody>
<row>
<entry>512</entry> <entry>2</entry> <entry>1</entry> <entry>4</entry> <entry>2MiB</entry>
</row>
<row>
<entry>512</entry> <entry>2</entry> <entry>2</entry> <entry>8</entry> <entry>4MiB</entry>
</row>
<row>
<entry>1k</entry> <entry>4</entry> <entry>2</entry> <entry>8</entry> <entry>8MiB</entry>
</row>
<row>
<entry>1k</entry> <entry>4</entry> <entry>4</entry> <entry>16</entry> <entry>16MiB</entry>
</row>
<row>
<entry>2k</entry> <entry>8</entry> <entry>4</entry> <entry>16</entry> <entry>32MiB</entry>
</row>
<row>
<entry>2k</entry> <entry>8</entry> <entry>8</entry> <entry>32</entry> <entry>64MiB</entry>
</row>
<row>
<entry>4k</entry> <entry>16</entry> <entry>8</entry> <entry>32</entry> <entry>128MiB</entry>
</row>
<row>
<entry>4k</entry> <entry>16</entry> <entry>16</entry> <entry>64</entry> <entry>256MiB</entry>
</row>
<row>
<entry>8k</entry> <entry>32</entry> <entry>16</entry> <entry>64</entry> <entry>512MiB</entry>
</row>
<row>
<entry>8k</entry> <entry>32</entry> <entry>32</entry> <entry>128</entry> <entry>1GiB</entry>
</row>
<row>
<entry>16k</entry> <entry>64</entry> <entry>32</entry> <entry>128</entry> <entry>2GiB</entry>
</row>
<row>
<entry>16k</entry> <entry>64</entry> <entry>64</entry> <entry>256</entry> <entry>4GiB</entry>
</row>
<row>
<entry>32k</entry> <entry>128</entry> <entry>64</entry> <entry>256</entry> <entry>8GiB</entry>
</row>
<row>
<entry>32k</entry> <entry>128</entry> <entry>128</entry> <entry>512</entry> <entry>16GiB</entry>
</row>
<row>
<entry>64k</entry> <entry>256</entry> <entry>128</entry> <entry>512</entry> <entry>32GiB</entry>
</row>
<row>
<entry>64k</entry> <entry>256</entry> <entry>256</entry> <entry>1024</entry> <entry>64GiB</entry>
</row>
<row>
<entry>128k</entry> <entry>512</entry> <entry>256</entry> <entry>1024</entry> <entry>128GiB</entry>
</row>
<row>
<entry>128k</entry> <entry>512</entry> <entry>512</entry> <entry>2048</entry> <entry>256GiB</entry>
</row>
<row>
<entry>256k</entry> <entry>1024</entry> <entry>512</entry> <entry>2048</entry> <entry>512GiB</entry>
</row>
<row>
<entry>256k</entry> <entry>1024</entry> <entry>1024</entry> <entry>4096</entry> <entry>1TiB</entry>
</row>
<row>
<entry>512k</entry> <entry>2048</entry> <entry>1024</entry> <entry>4096</entry> <entry>2TiB</entry>
</row>
<row>
<entry>512k</entry> <entry>2048</entry> <entry>2048</entry> <entry>8192</entry> <entry>4TiB</entry>
</row>
<row>
<entry>1024k</entry> <entry>4096</entry> <entry>2048</entry> <entry>8192</entry> <entry>8TiB</entry>
</row>
<row>
<entry>1024k</entry> <entry>4096</entry> <entry>4096</entry> <entry>16384</entry> <entry>16TiB</entry>
</row>
<row>
<entry>2048k</entry> <entry>8192</entry> <entry>4096</entry> <entry>16384</entry> <entry>32TiB</entry>
</row>
</tbody>
</tgroup>
</table>
</para>

</section>

<section>
<title>
        Redolog class description
</title>
<para>
The class <emphasis>redolog_t();</emphasis> implements the necessary
methods to create, open, close, read and write data to a redolog.
Managment of header catalog and sector bitmaps is done internally
by the class.
</para>
<section>
<title>
        Constants
</title>
<para>
<screen>
#define STANDARD_HEADER_MAGIC     "Bochs Virtual HD Image"
#define STANDARD_HEADER_VERSION   (0x00010000)
#define STANDARD_HEADER_SIZE      (512)
</screen>
These constants are used in the generic part of the header.
</para>

<para>
<screen>
#define REDOLOG_TYPE "Redolog"
#define REDOLOG_SUBTYPE_UNDOABLE "Undoable"
#define REDOLOG_SUBTYPE_VOLATILE "Volatile"
#define REDOLOG_SUBTYPE_GROWING  "Growing"
</screen>
These constants are used in the specific part of the header.
</para>

<para>
<screen>
#define REDOLOG_PAGE_NOT_ALLOCATED (0xffffffff)
</screen>
This constant is used in the catalog for an unwritten extent.
</para>

</section> <!-- Constants -->

<section> <title>Methods</title>
<para>
<emphasis>redolog_t();</emphasis> instanciates a new redolog.
</para>
<para>
<emphasis>int make_header (const char* type, Bit64u size);</emphasis> creates a header 
structure in memory, and sets its <emphasis>type</emphasis> and parameters based on the
disk image <emphasis>size</emphasis>. Returns 0.
</para>
<para>
<emphasis>int create (const char* filename, const char* type, Bit64u size);</emphasis> 
creates a new empty redolog file, with header and catalog, named <emphasis>filename</emphasis>
of type <emphasis>type</emphasis> for a <emphasis>size</emphasis> bytes image.
Returns 0 for OK or -1 if a problem occured.
</para>
<para>
<emphasis>int create (int filedes, const char* type, Bit64u size);</emphasis>
creates a new empty redolog file, with header and catalog, in a previously 
opened file described by <emphasis>filedes</emphasis>, of type <emphasis>type</emphasis> 
for a <emphasis>size</emphasis> bytes image.
Returns 0 for OK or -1 if a problem occured.
</para>
<para>
<emphasis>int open (const char* filename, const char* type, Bit64u size);</emphasis>
opens a redolog file named <emphasis>filename</emphasis>, and checks
for consistency of header values against a <emphasis>type</emphasis> and
<emphasis>size</emphasis>.
Returns 0 for OK or -1 if a problem occured.
</para>
<para>
<emphasis>void close ();</emphasis>
closes a redolog file.
</para>
<para>
<emphasis>off_t lseek (off_t offset, int whence);</emphasis>
seeks at logical data offset <emphasis>offset</emphasis> in a redolog.
<emphasis>offset</emphasis> must be a multiple of 512.
Only SEEK_SET is supported for <emphasis>whence</emphasis>.
Returns -1 if a problem occured, or the current logical offset in
the redolog.
</para>
<para>
<emphasis>ssize_t read (void* buf, size_t count);</emphasis>
reads <emphasis>count</emphasis> bytes of data of the redolog, from current logical offset,
and copies it into <emphasis>buf</emphasis>.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes read, that can be 0 if the data
has not previously be written to the redolog.
</para>
<para>
<emphasis>ssize_t write (const void* buf, size_t count);</emphasis>
writes <emphasis>count</emphasis> bytes of data from <emphasis>buf</emphasis> 
to the redolog, at current logical offset.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes written.
</para>

</section> 

</section> <!-- Redolog class description -->

<section>
<title>
        Disk image classes description
</title>
<para>
"volatile" and "undoable" disk images are easily implemented
by instanciating a <emphasis>default_image_t</emphasis> object (flat image) 
and a <emphasis>redolog_t</emphasis> object (redolog).
</para>
<para>
"growing" disk images only instanciates a <emphasis>redolog_t</emphasis> object.
</para>
<para>
Classe names are <emphasis>undoable_image_t</emphasis>, <emphasis>volatile_image_t</emphasis>
and <emphasis>growing_image_t</emphasis>.
</para>
<para>
When using these disk images, the underlying data structure and layout
is completely
hidden to the caller. Then, all offset and size values are "logical" values,
as if the disk was a flat file.
</para>
<section>
<title>
        Constants
</title>
<para>
<screen>
#define UNDOABLE_REDOLOG_EXTENSION ".redolog"
#define UNDOABLE_REDOLOG_EXTENSION_LENGTH (strlen(UNDOABLE_REDOLOG_EXTENSION))
#define VOLATILE_REDOLOG_EXTENSION ".XXXXXX"
#define VOLATILE_REDOLOG_EXTENSION_LENGTH (strlen(VOLATILE_REDOLOG_EXTENSION))
</screen>
These constants are used when building redolog file names
</para>
</section>

<section>
<title>
        undoable_image_t methods
</title>
<para>
<emphasis>
undoable_image_t(Bit64u size, const char* redolog_name);
</emphasis>
instanciates a new <emphasis>undoable_image_t</emphasis>
object. This disk image logical length is <emphasis>size</emphasis> bytes and
the redolog filename is <emphasis>redolog_name</emphasis>. 
</para>

<para>
<emphasis>
int open (const char* pathname);
</emphasis>
opens the flat disk image <emphasis>pathname</emphasis>,
as an undoable disk image. The associated redolog will
be named <emphasis>pathname</emphasis> with a 
<emphasis>UNDOABLE_REDOLOG_EXTENSION</emphasis>
suffix, unless set in the constructor.
Returns 0 for OK or -1 if a problem occured.
</para>

<para>
<emphasis>
void close ();
</emphasis>
closes the flat image and its redolog.
</para>

<para>
<emphasis>
off_t lseek (off_t offset, int whence);
</emphasis>
seeks at logical data position <emphasis>offset</emphasis> in
the undoable disk image. 
Only SEEK_SET is supported for <emphasis>whence</emphasis>.
Returns -1 if a problem occured, or the current logical
offset in the undoable disk image.
</para>

<para>
<emphasis>
ssize_t read (void* buf, size_t count);
</emphasis>
reads <emphasis>count</emphasis> bytes of data 
from the undoable disk image, from current logical offset,
and copies it into <emphasis>buf</emphasis>.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes read.
Data will be read from the redolog if it has
been previously written or from the flat image
otherwise.
</para>

<para>
<emphasis>
ssize_t write (const void* buf, size_t count);
</emphasis>
writes <emphasis>count</emphasis> bytes of data from <emphasis>buf</emphasis> 
to the undoable disk image, at current logical offset.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes written.
Data will always be written to the redolog.
</para>
</section>

<section>
<title>
        volatile_image_t methods
</title>
<para>
<emphasis>
volatile_image_t(Bit64u size, const char* redolog_name);
</emphasis>
instanciates a new <emphasis>volatile_image_t</emphasis>
object. This disk image logical length is <emphasis>size</emphasis> bytes and
the redolog filename is <emphasis>redolog_name</emphasis> plus a 
random suffix. 
</para>

<para>
<emphasis>
int open (const char* pathname);
</emphasis>
opens the flat disk image <emphasis>pathname</emphasis>,
as a volatile disk image. The associated redolog will
be named <emphasis>pathname</emphasis> with a 
random suffix, unless set in the constructor.
Returns 0 for OK or -1 if a problem occured.
</para>

<para>
<emphasis>
void close ();
</emphasis>
closes the flat image and its redolog.
The redolog is deleted/lost after close is called.
</para>

<para>
<emphasis>
off_t lseek (off_t offset, int whence);
</emphasis>
seeks at logical data position <emphasis>offset</emphasis> in
the volatile disk image. 
Only SEEK_SET is supported for <emphasis>whence</emphasis>.
Returns -1 if a problem occured, or the current logical offset in
the volatile disk image.
</para>

<para>
<emphasis>
ssize_t read (void* buf, size_t count);
</emphasis>
reads <emphasis>count</emphasis> bytes of data 
from the volatile disk image, from current logical offset,
and copies it into <emphasis>buf</emphasis>.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes read.
Data will be read from the redolog if it has
been previously written or from the flat image
otherwise.
</para>

<para>
<emphasis>
ssize_t write (const void* buf, size_t count);
</emphasis>
writes <emphasis>count</emphasis> bytes of data from <emphasis>buf</emphasis> 
to the volatile disk image, at current logical offset.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes written.
Data will always be written to the redolog.
</para>
</section>

<section>
<title>
        growing_image_t methods
</title>
<para>
<emphasis>
growing_image_t(Bit64u size);
</emphasis>
instanciates a new <emphasis>growing_image_t</emphasis>
object. This disk image logical length is <emphasis>size</emphasis> bytes.
</para>

<para>
<emphasis>
int open (const char* pathname);
</emphasis>
opens the growing disk image <emphasis>pathname</emphasis>,
Returns 0 for OK or -1 if a problem occured.
</para>

<para>
<emphasis>
void close ();
</emphasis>
closes the growing disk image.
</para>

<para>
<emphasis>
off_t lseek (off_t offset, int whence);
</emphasis>
seeks at logical data position <emphasis>offset</emphasis> in
the growable disk image. 
Only SEEK_SET is supported for <emphasis>whence</emphasis>.
Returns -1 if a problem occured, or the current logical offset in
the grwoing image.
</para>

<para>
<emphasis>
ssize_t read (void* buf, size_t count);
</emphasis>
reads <emphasis>count</emphasis> bytes of data 
from the growing disk image, from current logical offset,
and copies it into <emphasis>buf</emphasis>.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes read.
The buffer will be filled with null bytes if data
has not been previously written to the growing image.
</para>

<para>
<emphasis>
ssize_t write (const void* buf, size_t count);
</emphasis>
writes <emphasis>count</emphasis> bytes of data from <emphasis>buf</emphasis> 
to the growing disk image, at current logical offset.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes written.
</para>
</section>

</section>

</section>

</chapter>

<chapter id="debugger"><title>Debugger</title>
      <section><title>compile with debugger support</title>
      <para>
      &FIXME;
      </para>
      </section>
      <section id="debugger-get-started"><title>get started in debugger</title>
      <para>
      &FIXME;
      </para>
      </section>
      <section id="debugger-commands"><title>command reference</title>
      <para>
      &FIXME;
      </para>
      </section>
      <section id="debugger-techniques"><title>techniques</title>
      <para>
      &FIXME;
      </para>
      </section>
</chapter>

<chapter id="coding"><title>Coding</title>
      <section><title>coding conventions</title>
      <para>
      &FIXME;
      </para>
      </section>
      <section id="patches"><title>patches:</title>
      <para>
      &FIXME;
      how to make, where to submit, what happens then?
      </para>
      </section>

      <section id="cvs-release"><title>life cycle of a CVS release</title>
      <para>
      &FIXME;
      </para>
      </section>

</chapter>
</book>
