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/Documentation/sound/alsa/CMIPCI.txt

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  1              Brief Notes on C-Media 8738/8338 Driver
  2              =======================================
  3
  4                   Takashi Iwai <tiwai@suse.de>
  5
  6
  7Front/Rear Multi-channel Playback
  8---------------------------------
  9
 10CM8x38 chip can use ADC as the second DAC so that two different stereo
 11channels can be used for front/rear playbacks.  Since there are two
 12DACs, both streams are handled independently unlike the 4/6ch multi-
 13channel playbacks in the section below.
 14
 15As default, ALSA driver assigns the first PCM device (i.e. hw:0,0 for
 16card#0) for front and 4/6ch playbacks, while the second PCM device
 17(hw:0,1) is assigned to the second DAC for rear playback.
 18
 19There are slight difference between two DACs.
 20
 21- The first DAC supports U8 and S16LE formats, while the second DAC
 22  supports only S16LE.
 23- The seconde DAC supports only two channel stereo.
 24
 25Please note that the CM8x38 DAC doesn't support continuous playback
 26rate but only fixed rates: 5512, 8000, 11025, 16000, 22050, 32000,
 2744100 and 48000 Hz.
 28
 29The rear output can be heard only when "Four Channel Mode" switch is
 30disabled.  Otherwise no signal will be routed to the rear speakers.
 31As default it's turned on.
 32
 33*** WARNING ***
 34When "Four Channel Mode" switch is off, the output from rear speakers
 35will be FULL VOLUME regardless of Master and PCM volumes.
 36This might damage your audio equipment.  Please disconnect speakers
 37before your turn off this switch.
 38*** WARNING ***
 39
 40[ Well.. I once got the output with correct volume (i.e. same with the
 41  front one) and was so excited.  It was even with "Four Channel" bit
 42  on and "double DAC" mode.  Actually I could hear separate 4 channels
 43  from front and rear speakers!  But.. after reboot, all was gone.
 44  It's a very pity that I didn't save the register dump at that
 45  time..  Maybe there is an unknown register to achieve this... ]
 46
 47If your card has an extra output jack for the rear output, the rear
 48playback should be routed there as default.  If not, there is a
 49control switch in the driver "Line-In As Rear", which you can change
 50via alsamixer or somewhat else.  When this switch is on, line-in jack
 51is used as rear output.
 52
 53There are two more controls regarding to the rear output.
 54The "Exchange DAC" switch is used to exchange front and rear playback
 55routes, i.e. the 2nd DAC is output from front output.
 56
 57
 584/6 Multi-Channel Playback
 59--------------------------
 60
 61The recent CM8738 chips support for the 4/6 multi-channel playback
 62function.  This is useful especially for AC3 decoding.
 63
 64When the multi-channel is supported, the driver name has a suffix
 65"-MC" such like "CMI8738-MC6".  You can check this name from
 66/proc/asound/cards.
 67
 68When the 4/6-ch output is enabled, the second DAC accepts up to 6 (or
 694) channels.  While the dual DAC supports two different rates or
 70formats, the 4/6-ch playback supports only the same condition for all
 71channels.  Since the multi-channel playback mode uses both DACs, you
 72cannot operate with full-duplex.
 73
 74The 4.0 and 5.1 modes are defined as the pcm "surround40" and "surround51"
 75in alsa-lib.  For example, you can play a WAV file with 6 channels like
 76
 77	% aplay -Dsurround51 sixchannels.wav
 78
 79For programmin the 4/6 channel playback, you need to specify the PCM
 80channels as you like and set the format S16LE.  For example, for playback
 81with 4 channels,
 82
 83	snd_pcm_hw_params_set_access(pcm, hw, SND_PCM_ACCESS_RW_INTERLEAVED);
 84	    // or mmap if you like
 85	snd_pcm_hw_params_set_format(pcm, hw, SND_PCM_FORMAT_S16_LE);
 86	snd_pcm_hw_params_set_channels(pcm, hw, 4);
 87
 88and use the interleaved 4 channel data.
 89
 90There are some control switchs affecting to the speaker connections:
 91
 92"Line-In As Rear"	- As mentioned above, the line-in jack is used
 93	for the rear (3th and 4th channels) output.
 94"Line-In As Bass"	- The line-in jack is used for the bass (5th
 95	and 6th channels) output.
 96"Mic As Center/LFE"	- The mic jack is used for the bass output.
 97	If this switch is on, you cannot use a microphone as a capture
 98	source, of course.
 99
100
101Digital I/O
102-----------
103
104The CM8x38 provides the excellent SPDIF capability with very chip
105price (yes, that's the reason I bought the card :)
106
107The SPDIF playback and capture are done via the third PCM device
108(hw:0,2).  Usually this is assigned to the PCM device "spdif".
109The available rates are 44100 and 48000 Hz.
110For playback with aplay, you can run like below:
111
112	% aplay -Dhw:0,2 foo.wav
113
114or
115
116	% aplay -Dspdif foo.wav
117
11824bit format is also supported experimentally.
119
120The playback and capture over SPDIF use normal DAC and ADC,
121respectively, so you cannot playback both analog and digital streams
122simultaneously.
123
124To enable SPDIF output, you need to turn on "IEC958 Output Switch"
125control via mixer or alsactl.  Then you'll see the red light on from
126the card so you know that's working obviously :)
127The SPDIF input is always enabled, so you can hear SPDIF input data
128from line-out with "IEC958 In Monitor" switch at any time (see
129below).
130
131You can play via SPDIF even with the first device (hw:0,0),
132but SPDIF is enabled only when the proper format (S16LE), sample rate
133(441100 or 48000) and channels (2) are used.  Otherwise it's turned
134off.  (Also don't forget to turn on "IEC958 Output Switch", too.)
135
136
137Additionally there are relevant control switches:
138
139"IEC958 Mix Analog" - Mix analog PCM playback and FM-OPL/3 streams and
140	output through SPDIF.  This switch appears only on old chip
141	models (CM8738 033 and 037).
142	Note: without this control you can output PCM to SPDIF.
143	This is "mixing" of streams, so e.g. it's not for AC3 output
144	(see the next section).
145
146"IEC958 In Select"  - Select SPDIF input, the internal CD-in (false)
147	and the external input (true).
148
149"IEC958 Loop"       - SPDIF input data is loop back into SPDIF
150	output (aka bypass)
151
152"IEC958 Copyright"  - Set the copyright bit.
153
154"IEC958 5V"         - Select 0.5V (coax) or 5V (optical) interface.
155	On some cards this doesn't work and you need to change the
156	configuration with hardware dip-switch.
157
158"IEC958 In Monitor" - SPDIF input is routed to DAC.
159
160"IEC958 In Phase Inverse" - Set SPDIF input format as inverse.
161	[FIXME: this doesn't work on all chips..]
162
163"IEC958 In Valid"   - Set input validity flag detection.
164
165Note: When "PCM Playback Switch" is on, you'll hear the digital output
166stream through analog line-out.
167
168
169The AC3 (RAW DIGITAL) OUTPUT
170----------------------------
171
172The driver supports raw digital (typically AC3) i/o over SPDIF.  This
173can be toggled via IEC958 playback control, but usually you need to
174access it via alsa-lib.  See alsa-lib documents for more details.
175
176On the raw digital mode, the "PCM Playback Switch" is automatically
177turned off so that non-audio data is heard from the analog line-out.
178Similarly the following switches are off: "IEC958 Mix Analog" and
179"IEC958 Loop".  The switches are resumed after closing the SPDIF PCM
180device automatically to the previous state.
181
182On the model 033, AC3 is implemented by the software conversion in
183the alsa-lib.  If you need to bypass the software conversion of IEC958
184subframes, pass the "soft_ac3=0" module option.  This doesn't matter
185on the newer models.
186
187
188ANALOG MIXER INTERFACE
189----------------------
190
191The mixer interface on CM8x38 is similar to SB16.
192There are Master, PCM, Synth, CD, Line, Mic and PC Speaker playback
193volumes.  Synth, CD, Line and Mic have playback and capture switches,
194too, as well as SB16.
195
196In addition to the standard SB mixer, CM8x38 provides more functions.
197- PCM playback switch
198- PCM capture switch (to capture the data sent to DAC)
199- Mic Boost switch
200- Mic capture volume
201- Aux playback volume/switch and capture switch
202- 3D control switch
203
204
205MIDI CONTROLLER
206---------------
207
208The MPU401-UART interface is enabled as default only for the first
209(CMIPCI) card.  You need to set module option "midi_port" properly
210for the 2nd (CMIPCI) card.
211
212There is _no_ hardware wavetable function on this chip (except for
213OPL3 synth below).
214What's said as MIDI synth on Windows is a software synthesizer
215emulation.  On Linux use TiMidity or other softsynth program for
216playing MIDI music.
217
218
219FM OPL/3 Synth
220--------------
221
222The FM OPL/3 is also enabled as default only for the first card.
223Set "fm_port" module option for more cards.
224
225The output quality of FM OPL/3 is, however, very weird.
226I don't know why..
227
228
229Joystick and Modem
230------------------
231
232The joystick and modem should be available by enabling the control
233switch "Joystick" and "Modem" respectively.  But I myself have never
234tested them yet.
235
236
237Debugging Information
238---------------------
239
240The registers are shown in /proc/asound/cardX/cmipci.  If you have any
241problem (especially unexpected behavior of mixer), please attach the
242output of this proc file together with the bug report.