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+              Brief Notes on C-Media 8738/8338 Driver
+              =======================================
+
+                   Takashi Iwai <tiwai@suse.de>
+
+
+Front/Rear Multi-channel Playback
+---------------------------------
+
+CM8x38 chip can use ADC as the second DAC so that two different stereo
+channels can be used for front/rear playbacks.  Since there are two
+DACs, both streams are handled independently unlike the 4/6ch multi-
+channel playbacks in the section below.
+
+As default, ALSA driver assigns the first PCM device (i.e. hw:0,0 for
+card#0) for front and 4/6ch playbacks, while the second PCM device
+(hw:0,1) is assigned to the second DAC for rear playback.
+
+There are slight difference between two DACs.
+
+- The first DAC supports U8 and S16LE formats, while the second DAC
+  supports only S16LE.
+- The seconde DAC supports only two channel stereo.
+
+Please note that the CM8x38 DAC doesn't support continuous playback
+rate but only fixed rates: 5512, 8000, 11025, 16000, 22050, 32000,
+44100 and 48000 Hz.
+
+The rear output can be heard only when "Four Channel Mode" switch is
+disabled.  Otherwise no signal will be routed to the rear speakers.
+As default it's turned on.
+
+*** WARNING ***
+When "Four Channel Mode" switch is off, the output from rear speakers
+will be FULL VOLUME regardless of Master and PCM volumes.
+This might damage your audio equipment.  Please disconnect speakers
+before your turn off this switch.
+*** WARNING ***
+
+[ Well.. I once got the output with correct volume (i.e. same with the
+  front one) and was so excited.  It was even with "Four Channel" bit
+  on and "double DAC" mode.  Actually I could hear separate 4 channels
+  from front and rear speakers!  But.. after reboot, all was gone.
+  It's a very pity that I didn't save the register dump at that
+  time..  Maybe there is an unknown register to achieve this... ]
+
+If your card has an extra output jack for the rear output, the rear
+playback should be routed there as default.  If not, there is a
+control switch in the driver "Line-In As Rear", which you can change
+via alsamixer or somewhat else.  When this switch is on, line-in jack
+is used as rear output.
+
+There are two more controls regarding to the rear output.
+The "Exchange DAC" switch is used to exchange front and rear playback
+routes, i.e. the 2nd DAC is output from front output.
+
+
+4/6 Multi-Channel Playback
+--------------------------
+
+The recent CM8738 chips support for the 4/6 multi-channel playback
+function.  This is useful especially for AC3 decoding.
+
+When the multi-channel is supported, the driver name has a suffix
+"-MC" such like "CMI8738-MC6".  You can check this name from
+/proc/asound/cards.
+
+When the 4/6-ch output is enabled, the second DAC accepts up to 6 (or
+4) channels.  While the dual DAC supports two different rates or
+formats, the 4/6-ch playback supports only the same condition for all
+channels.  Since the multi-channel playback mode uses both DACs, you
+cannot operate with full-duplex.
+
+The 4.0 and 5.1 modes are defined as the pcm "surround40" and "surround51"
+in alsa-lib.  For example, you can play a WAV file with 6 channels like
+
+        % aplay -Dsurround51 sixchannels.wav
+
+For programmin the 4/6 channel playback, you need to specify the PCM
+channels as you like and set the format S16LE.  For example, for playback
+with 4 channels,
+
+        snd_pcm_hw_params_set_access(pcm, hw, SND_PCM_ACCESS_RW_INTERLEAVED);
+            // or mmap if you like
+        snd_pcm_hw_params_set_format(pcm, hw, SND_PCM_FORMAT_S16_LE);
+        snd_pcm_hw_params_set_channels(pcm, hw, 4);
+
+and use the interleaved 4 channel data.
+
+There are some control switchs affecting to the speaker connections:
+
+"Line-In As Rear"       - As mentioned above, the line-in jack is used
+        for the rear (3th and 4th channels) output.
+"Line-In As Bass"       - The line-in jack is used for the bass (5th
+        and 6th channels) output.
+"Mic As Center/LFE"     - The mic jack is used for the bass output.
+        If this switch is on, you cannot use a microphone as a capture
+        source, of course.
+
+
+Digital I/O
+-----------
+
+The CM8x38 provides the excellent SPDIF capability with very chip
+price (yes, that's the reason I bought the card :)
+
+The SPDIF playback and capture are done via the third PCM device
+(hw:0,2).  Usually this is assigned to the PCM device "spdif".
+The available rates are 44100 and 48000 Hz.
+For playback with aplay, you can run like below:
+
+        % aplay -Dhw:0,2 foo.wav
+
+or
+
+        % aplay -Dspdif foo.wav
+
+24bit format is also supported experimentally.
+
+The playback and capture over SPDIF use normal DAC and ADC,
+respectively, so you cannot playback both analog and digital streams
+simultaneously.
+
+To enable SPDIF output, you need to turn on "IEC958 Output Switch"
+control via mixer or alsactl.  Then you'll see the red light on from
+the card so you know that's working obviously :)
+The SPDIF input is always enabled, so you can hear SPDIF input data
+from line-out with "IEC958 In Monitor" switch at any time (see
+below).
+
+You can play via SPDIF even with the first device (hw:0,0),
+but SPDIF is enabled only when the proper format (S16LE), sample rate
+(441100 or 48000) and channels (2) are used.  Otherwise it's turned
+off.  (Also don't forget to turn on "IEC958 Output Switch", too.)
+
+
+Additionally there are relevant control switches:
+
+"IEC958 Mix Analog" - Mix analog PCM playback and FM-OPL/3 streams and
+        output through SPDIF.  This switch appears only on old chip
+        models (CM8738 033 and 037).
+        Note: without this control you can output PCM to SPDIF.
+        This is "mixing" of streams, so e.g. it's not for AC3 output
+        (see the next section).
+
+"IEC958 In Select"  - Select SPDIF input, the internal CD-in (false)
+        and the external input (true).
+
+"IEC958 Loop"       - SPDIF input data is loop back into SPDIF
+        output (aka bypass)
+
+"IEC958 Copyright"  - Set the copyright bit.
+
+"IEC958 5V"         - Select 0.5V (coax) or 5V (optical) interface.
+        On some cards this doesn't work and you need to change the
+        configuration with hardware dip-switch.
+
+"IEC958 In Monitor" - SPDIF input is routed to DAC.
+
+"IEC958 In Phase Inverse" - Set SPDIF input format as inverse.
+        [FIXME: this doesn't work on all chips..]
+
+"IEC958 In Valid"   - Set input validity flag detection.
+
+Note: When "PCM Playback Switch" is on, you'll hear the digital output
+stream through analog line-out.
+
+
+The AC3 (RAW DIGITAL) OUTPUT
+----------------------------
+
+The driver supports raw digital (typically AC3) i/o over SPDIF.  This
+can be toggled via IEC958 playback control, but usually you need to
+access it via alsa-lib.  See alsa-lib documents for more details.
+
+On the raw digital mode, the "PCM Playback Switch" is automatically
+turned off so that non-audio data is heard from the analog line-out.
+Similarly the following switches are off: "IEC958 Mix Analog" and
+"IEC958 Loop".  The switches are resumed after closing the SPDIF PCM
+device automatically to the previous state.
+
+On the model 033, AC3 is implemented by the software conversion in
+the alsa-lib.  If you need to bypass the software conversion of IEC958
+subframes, pass the "soft_ac3=0" module option.  This doesn't matter
+on the newer models.
+
+
+ANALOG MIXER INTERFACE
+----------------------
+
+The mixer interface on CM8x38 is similar to SB16.
+There are Master, PCM, Synth, CD, Line, Mic and PC Speaker playback
+volumes.  Synth, CD, Line and Mic have playback and capture switches,
+too, as well as SB16.
+
+In addition to the standard SB mixer, CM8x38 provides more functions.
+- PCM playback switch
+- PCM capture switch (to capture the data sent to DAC)
+- Mic Boost switch
+- Mic capture volume
+- Aux playback volume/switch and capture switch
+- 3D control switch
+
+
+MIDI CONTROLLER
+---------------
+
+The MPU401-UART interface is enabled as default only for the first
+(CMIPCI) card.  You need to set module option "midi_port" properly
+for the 2nd (CMIPCI) card.
+
+There is _no_ hardware wavetable function on this chip (except for
+OPL3 synth below).
+What's said as MIDI synth on Windows is a software synthesizer
+emulation.  On Linux use TiMidity or other softsynth program for
+playing MIDI music.
+
+
+FM OPL/3 Synth
+--------------
+
+The FM OPL/3 is also enabled as default only for the first card.
+Set "fm_port" module option for more cards.
+
+The output quality of FM OPL/3 is, however, very weird.
+I don't know why..
+
+
+Joystick and Modem
+------------------
+
+The joystick and modem should be available by enabling the control
+switch "Joystick" and "Modem" respectively.  But I myself have never
+tested them yet.
+
+
+Debugging Information
+---------------------
+
+The registers are shown in /proc/asound/cardX/cmipci.  If you have any
+problem (especially unexpected behavior of mixer), please attach the
+output of this proc file together with the bug report.