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flash-linux0.11-talk/一些非必要的资料/linux-0.11-quickstart/Bochs-2.3.6/docs/development/sb16-emulation-basics.html

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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><DIV
CLASS="SECTION"
><H1
CLASS="SECTION"
><A
NAME="SB16-EMULATION-BASICS"
>2.8. Sound Blaster 16 Emulation</A
></H1
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> A little more up-to-date version of the user related part of this section is
available in the <A
HREF="../user/sb16-emulation.html"
TARGET="_top"
>user guide</A
>.</P
></BLOCKQUOTE
></DIV
><P
>Sound Blaster 16 (SB16) emulation for Bochs was written and donated by
Josef Drexler, who has a
<A
HREF="http://publish.uwo.ca/~jdrexler/bochs/"
TARGET="_top"
>web page</A
> on the topic.
The entire set of his SB16 patches have been integrated into
Bochs, however, so you can find everything you need here.</P
><P
>SB16 Emulation has been tested with several soundcards and versions of Linux. Please give
Josef <A
HREF="mailto:jdrexler@julian.uwo.ca"
TARGET="_top"
>feedback</A
> on
whether is does or doesn't work on your combination of software and hardware.</P
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN283"
>2.8.1. How well does it work?</A
></H2
><P
>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.</P
><P
>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.</P
><P
>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.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN288"
>2.8.2. Output to a sound card</A
></H2
><P
>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.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN291"
>2.8.3. Installation on Linux</A
></H2
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>Prerequisites:</I
></SPAN
></P
><P
>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. </P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN296"
>2.8.4. Configuring Bochs</A
></H2
><P
>There are a few values in config.h that are relevant to the sound functions.
Edit config.h after running configure, but before compiling.</P
><P
>BX_USE_SB16_SMF should be 1 unless you intend to have several sound cards
running at the same time.</P
><P
>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.</P
><P
>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:</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="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.</PRE
></TD
></TR
></TABLE
><P
>Setup the SB16 emulation in your .bochsrc, according to instructions
in that file.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN304"
>2.8.5. Runtime configuration</A
></H2
><P
>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
<A
HREF="http://publish.uwo.ca/~jdrexler/bochs/"
TARGET="_top"
>executable</A
>.</P
><P
>See the section "Sound Blaster 16 Emulation" in the user documentation for
information about the commands of SB16CTRL.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN309"
>2.8.6. Features planned for the future</A
></H2
><P
></P
><UL
><LI
><P
>Ports to more OS's, but I can't do this myself</P
></LI
><LI
><P
>Finishing the OPL3 FM emulation by translating the music to midi data</P
></LI
></UL
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN316"
>2.8.7. Description of the sound output classes</A
></H2
><P
>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.</P
><P
>You should also have a look at the exisiting files, <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>SOUNDLNX.CC</I
></SPAN
>
for Linux and <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>SOUNDWIN.CC</I
></SPAN
> for Windows and their respective
header files to get an idea about how these things really work.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN322"
>2.8.8. Files</A
></H2
><P
>The main include file is <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>bochs.h</I
></SPAN
>. It has all definitions
for the system-independent functions that the SB16 emulation uses, which
are defined in <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>sb16.h</I
></SPAN
>.</P
><P
>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.</P
><P
>To actually make the emulator use any specific driver,
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>BX_SOUND_OUTPUT_C</I
></SPAN
> has to be set to the name of the respective
output class.</P
><P
>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 <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>#if defined</I
></SPAN
> (OS-define) construct.
Also don't forget to add your file to the object list in
iodev/Makefile and iodev/Makefile.in.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN332"
>2.8.9. Classes</A
></H2
><P
>The following classes are involved with the SB16 emulation:</P
><P
></P
><UL
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>bx_sb16_c</I
></SPAN
> 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.</P
></LI
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>bx_sound_output_c</I
></SPAN
> 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.</P
></LI
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>bx_sound_OS_c</I
></SPAN
> is derived from
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>bx_sound_output_c</I
></SPAN
>. It contains the code to generate
output for the <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>OS</I
></SPAN
> 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 <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>virtual</I
></SPAN
> if and only if <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>BX_USE_SOUND_VIRTUAL</I
></SPAN
>
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.</P
></LI
></UL
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN349"
>2.8.10. Methods</A
></H2
><P
>The following are the methods that the output class has to override.
All but constructor and destructor have to return either
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>BX_SOUND_OUTPUT_OK</I
></SPAN
> <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>(0)</I
></SPAN
> if the function was successful,
or <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>BX_SOUND_OUTPUT_ERR</I
></SPAN
> <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>(1)</I
></SPAN
> if not. If any of the initialization
functions fail, output to that device is disabled until the emulator is restarted.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN356"
>2.8.11. bx_sound_OS_c(bx_sb16_c*sb16)</A
></H2
><P
>The emulator instantiates the class at the initialization of Bochs.</P
><P
>Description of the parameter:</P
><P
></P
><UL
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>sb16</I
></SPAN
> is a pointer to the emulator class.
This pointer can then be used to access for example the <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>writelog</I
></SPAN
> function to generate
sound-related log messages. Apart from that, no access to the emulator
should be necessary.</P
></LI
><LI
><P
>The constructor should <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> allocate the output devices.
This shouldn't be done until the actual output occurs; in either
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>initmidioutput()</I
></SPAN
> or <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>initwaveoutput()</I
></SPAN
>.
Otherwise it would be impossible to have two copies of Bochs running
concurrently (if anybody ever wants to do this).</P
></LI
></UL
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN370"
>2.8.12. ~bx_sound_OS_c()</A
></H2
><P
>The instance is destroyed just before Bochs ends.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN373"
>2.8.13. int openmidioutput(char *device)</A
></H2
><P
></P
><UL
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>openmidioutput()</I
></SPAN
> 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.</P
></LI
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>openmidioutput()</I
></SPAN
> will always be called before <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>openwaveoutput()</I
></SPAN
>,
and <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>closemidioutput()</I
></SPAN
>will always be called before <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>closewaveoutput()</I
></SPAN
>, but not in all cases will both functions be called.</P
></LI
></UL
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN385"
>2.8.14. Description of the parameters:</A
></H2
><P
></P
><UL
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>device</I
></SPAN
> is a system-dependent variable.
It contains the value of the <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>MIDI=device</I
></SPAN
> configuration option.</P
></LI
><LI
><P
>Note that only one midi output device will be used at any one time.
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>device</I
></SPAN
>
may not have the same value throughout one session, but it will be closed
before it is changed.</P
></LI
></UL
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN395"
>2.8.15. int midiready()</A
></H2
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>midiready()</I
></SPAN
> is called whenever the applications asks if the
midi queue can accept more data. </P
><P
>Return values:</P
><P
></P
><UL
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>BX_SOUND_OUTPUT_OK</I
></SPAN
> if the midi output device is ready. </P
></LI
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>BX_SOUND_OUTPUT_ERR</I
></SPAN
> if it isn't ready. </P
></LI
></UL
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>Note: </I
></SPAN
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>midiready()</I
></SPAN
> will be called a few times
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>before</I
></SPAN
> the device is opened. If this is the case, it should
always report that it is ready, otherwise the application (not Bochs)
will hang.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN411"
>2.8.16. int sendmidicommand(int delta, int command, int length, Bit8u data[])</A
></H2
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>sendmidicommand()</I
></SPAN
>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.</P
><P
>Description of the parameters:</P
><P
></P
><UL
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>delta</I
></SPAN
> 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.</P
></LI
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>command</I
></SPAN
> 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.</P
></LI
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>length</I
></SPAN
> is the number of data bytes that
are contained in the data structure. This does <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> include the status
byte which is not replicated in the data array. It can only be greater
than 3 for SysEx messages (commands <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>0xF0</I
></SPAN
> and <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>0xF7</I
></SPAN
>)</P
></LI
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>data[]</I
></SPAN
> is the array of these data bytes,
in the order they have in the standard MIDI specification.
Note, it might be <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>NULL</I
></SPAN
> if length==0.</P
></LI
></UL
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN433"
>2.8.17. int closemidioutput()</A
></H2
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>closemidioutput()</I
></SPAN
> is called before shutting down Bochs or
when the
emulator gets the <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>stop_output</I
></SPAN
> command through the emulator port.
After this, no more output will be necessary until <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>openmidioutput()</I
></SPAN
>
is called again, but <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>midiready()</I
></SPAN
> might still be called. It should do the following:</P
><P
></P
><UL
><LI
><P
>Wait for all remaining messages to be completed</P
></LI
><LI
><P
>Reset and close the midi output device</P
></LI
></UL
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN445"
>2.8.18. int openwaveoutput(char *device)</A
></H2
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>openwaveoutput()</I
></SPAN
> is called when the first wave output occurs,
and only if the selected wavemode is 1. It should do the following:</P
><P
></P
><UL
><LI
><P
>Open the given device, and prepare it for wave output</P
></LI
></UL
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>or</I
></SPAN
></P
><P
></P
><UL
><LI
><P
>Store the device name so that the device can be opened in <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>startplayback()</I
></SPAN
>.</P
></LI
></UL
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>openmidioutput()</I
></SPAN
> will always be called before <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>openwaveoutput()</I
></SPAN
>,
and <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>closemidioutput()</I
></SPAN
>will always be called before <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>closewaveoutput()</I
></SPAN
>, but not in all cases will both functions be called.</P
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>openwaveoutput()</I
></SPAN
> will typically be called once, whereas
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>startplayback()</I
></SPAN
> 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
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>startplayback()</I
></SPAN
> as opposed to <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>openwaveoutput()</I
></SPAN
>
to ensure that it can be used by other applications while Bochs doesn't
need it.</P
><P
>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
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>startwaveplayback</I
></SPAN
> function will be called very often, and it
isn't a good idea to have it reopen the device every time.</P
><P
>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.</P
><P
>The parameters are the following: </P
><P
></P
><UL
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>device</I
></SPAN
> is the wave device selected by
the user. It is strictly system-dependent. The value is that of the
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>WAVE=device</I
></SPAN
>
configuration option.</P
></LI
></UL
><P
>Note that only one wave output device will be used at any one time.
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>device</I
></SPAN
> may not have the same value throughout one session, but it will be closed
before it is changed.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN479"
>2.8.19. int startwaveplayback(int frequency, int bits, int stereo, int format)</A
></H2
><P
>This function is called whenever the application starts a new DMA transfer. It should do the following:</P
><P
></P
><UL
><LI
><P
>Open the wave output device, unless <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>openwaveoutput()</I
></SPAN
> did that
already</P
></LI
><LI
><P
>Prepare the device for data and set the device parameters to those given
in the function call</P
></LI
></UL
><P
>The parameters are the following:</P
><P
></P
><UL
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>frequency</I
></SPAN
> is the desired frequency of the
output. Because of the capabities of the SB16, it can have any value between
5000 and 44,100.</P
></LI
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>bits</I
></SPAN
> is either 8 or 16, denoting the resolution
of one sample.</P
></LI
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>stereo</I
></SPAN
> is either 1 for stereo output, or 0 for mono output.</P
></LI
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>format</I
></SPAN
> is a bit-coded value (see below).</P
></LI
></UL
><P
><DIV
CLASS="TABLE"
><A
NAME="AEN503"
></A
><P
><B
>Table 2-4. format bits</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><THEAD
><TR
><TH
>Bit number</TH
><TH
>Meaning</TH
></TR
></THEAD
><TBODY
><TR
><TD
> 0 (LSB) </TD
><TD
><P
> 0: unsigned data </P
><P
> 1: signed data </P
></TD
></TR
><TR
><TD
> 1..6 </TD
><TD
> Type of codec (see below) </TD
></TR
><TR
><TD
> 7 </TD
><TD
><P
> 0: no reference byte </P
><P
> 1: with reference byte </P
></TD
></TR
><TR
><TD
> 8..x </TD
><TD
> reserved (0) </TD
></TR
></TBODY
></TABLE
></DIV
>
<DIV
CLASS="TABLE"
><A
NAME="AEN527"
></A
><P
><B
>Table 2-5. codecs</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><THEAD
><TR
><TH
>Value</TH
><TH
>Meaning</TH
></TR
></THEAD
><TBODY
><TR
><TD
> 0 </TD
><TD
> PCM (raw data) </TD
></TR
><TR
><TD
> 1 </TD
><TD
> reserved </TD
></TR
><TR
><TD
> 2 </TD
><TD
> 2-bit ADPCM (Creative Labs format) </TD
></TR
><TR
><TD
> 3 </TD
><TD
> 2.4-bit (3-bit) ADPCM (Creative Labs format) </TD
></TR
><TR
><TD
> 4 </TD
><TD
> 4-bit ADPCM (Creative Labs format) </TD
></TR
></TBODY
></TABLE
></DIV
></P
><P
>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.</P
><P
>The number of bytes per sample can be calculated from this as (bits / 8) * (stereo + 1).</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN552"
>2.8.20. int waveready()</A
></H2
><P
>This is called whenever the emulator has another output buffer ready
and would like to pass it to the output class. This happens every
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>BX_SOUND_OUTPUT_WAVEPACKETSIZE</I
></SPAN
> bytes, or whenever a DMA transfer
is done or aborted.</P
><P
>It should return whether the output device is ready for another buffer
of <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>BX_SOUND_OUTPUT_WAVEPACKETSIZE</I
></SPAN
> bytes.
If <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>BX_SOUND_OUTPUT_ERR</I
></SPAN
>
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.</P
><P
>As opposed to <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>midiready(), waveready()</I
></SPAN
> will <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> be
called unless the device is open.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN562"
>2.8.21. int sendwavepacket(int length, Bit8u data[])</A
></H2
><P
>This function is called whenever a data packet of at most <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>BX_SB16_WAVEPACKETSIZE</I
></SPAN
>
is ready at the SB16 emulator. It should then do the following:</P
><P
></P
><UL
><LI
><P
>Send this wave packet to the wave hardware</P
></LI
></UL
><P
>This function <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>has</I
></SPAN
> to be synchronous, meaning that it <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>has</I
></SPAN
>
to return immediately, and <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> 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, <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>waveready()</I
></SPAN
> should return <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>BX_SOUND_OUTPUT_ERR</I
></SPAN
>
until the device accepts another block of data.</P
><P
>Parameters:</P
><P
></P
><UL
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>length</I
></SPAN
> is the number of data bytes in
the data stream. It will never be larger than <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>BX_SB16_WAVEPACKETSIZE</I
></SPAN
>.</P
></LI
><LI
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>data</I
></SPAN
> is the array of data bytes.</P
></LI
></UL
><P
>The order of bytes in the data stream is the same as that in the Wave file format:
<DIV
CLASS="TABLE"
><A
NAME="AEN585"
></A
><P
><B
>Table 2-6. wave output types</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><THEAD
><TR
><TH
>Output type</TH
><TH
>Sequence of data bytes</TH
></TR
></THEAD
><TBODY
><TR
><TD
> 8 bit mono </TD
><TD
> Sample 1; Sample 2; Sample 3; etc. </TD
></TR
><TR
><TD
> 8 bit stereo </TD
><TD
> Sample 1, Channel 0; Sample 1, Channel 1; Sample 2, Channel 0; Sample 2, Channel 1; etc. </TD
></TR
><TR
><TD
> 16 bit mono </TD
><TD
> Sample 1, LSB; Sample 1, MSB; Sample 2, LSB; Sample 2, MSB; etc. </TD
></TR
><TR
><TD
> 16 bit stereo </TD
><TD
> Sample 1, LSB, Channel 0; Sample 1, MSB, Channel 0; Sample 1, LSB, Channel 1; Sample 1, MSB, Channel 1; etc. </TD
></TR
></TBODY
></TABLE
></DIV
></P
><P
>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.</P
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN606"
>2.8.22. int stopwaveplayback()</A
></H2
><P
>This function is called at the end of a DMA transfer. It should do the following:</P
><P
></P
><UL
><LI
><P
>Close the output device if it was opened by <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>startwaveplayback()</I
></SPAN
>.
and it's not going to be opened soon. Which is almost impossible to tell.</P
></LI
></UL
></DIV
><DIV
CLASS="SECTION"
><H2
CLASS="SECTION"
><A
NAME="AEN613"
>2.8.23. int closewaveoutput()</A
></H2
><P
>This function is called just before Bochs exits. It should do the following:</P
><P
></P
><UL
><LI
><P
> Close the output device, if this hasn't been done by <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>stopwaveplayback()</I
></SPAN
>.</P
></LI
></UL
><P
>Typically, <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>stopwaveplayback()</I
></SPAN
> will be called several times, whenever
a DMA transfer is done, where <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>closewaveoutput()</I
></SPAN
> will only be called
once. However, in the future it might be possible that <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>openwaveoutput()</I
></SPAN
>
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.</P
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