1         Brief Notes on C-Media 8338/8738/8768/8770 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 differences between the two DACs:
20
21- The first DAC supports U8 and S16LE formats, while the second DAC
22  supports only S16LE.
23- The second 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 programming 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 switches affecting to the speaker connections:
91
92"Line-In Mode"	- an enum control to change the behavior of line-in
93	jack.  Either "Line-In", "Rear Output" or "Bass Output" can
94	be selected.  The last item is available only with model 039
95	or newer. 
96	When "Rear Output" is chosen, the surround channels 3 and 4
97	are output to line-in jack.
98"Mic-In Mode"	- an enum control to change the behavior of mic-in
99	jack.  Either "Mic-In" or "Center/LFE Output" can be
100	selected. 
101	When "Center/LFE Output" is chosen, the center and bass
102	channels (channels 5 and 6) are output to mic-in jack. 
103
104Digital I/O
105-----------
106
107The CM8x38 provides the excellent SPDIF capability with very cheap
108price (yes, that's the reason I bought the card :)
109
110The SPDIF playback and capture are done via the third PCM device
111(hw:0,2).  Usually this is assigned to the PCM device "spdif".
112The available rates are 44100 and 48000 Hz.
113For playback with aplay, you can run like below:
114
115	% aplay -Dhw:0,2 foo.wav
116
117or
118
119	% aplay -Dspdif foo.wav
120
12124bit format is also supported experimentally.
122
123The playback and capture over SPDIF use normal DAC and ADC,
124respectively, so you cannot playback both analog and digital streams
125simultaneously.
126
127To enable SPDIF output, you need to turn on "IEC958 Output Switch"
128control via mixer or alsactl ("IEC958" is the official name of
129so-called S/PDIF).  Then you'll see the red light on from the card so
130you know that's working obviously :)
131The SPDIF input is always enabled, so you can hear SPDIF input data
132from line-out with "IEC958 In Monitor" switch at any time (see
133below).
134
135You can play via SPDIF even with the first device (hw:0,0),
136but SPDIF is enabled only when the proper format (S16LE), sample rate
137(441100 or 48000) and channels (2) are used.  Otherwise it's turned
138off.  (Also don't forget to turn on "IEC958 Output Switch", too.)
139
140
141Additionally there are relevant control switches:
142
143"IEC958 Mix Analog" - Mix analog PCM playback and FM-OPL/3 streams and
144	output through SPDIF.  This switch appears only on old chip
145	models (CM8738 033 and 037).
146	Note: without this control you can output PCM to SPDIF.
147	This is "mixing" of streams, so e.g. it's not for AC3 output
148	(see the next section).
149
150"IEC958 In Select"  - Select SPDIF input, the internal CD-in (false)
151	and the external input (true).
152
153"IEC958 Loop"       - SPDIF input data is loop back into SPDIF
154	output (aka bypass)
155
156"IEC958 Copyright"  - Set the copyright bit.
157
158"IEC958 5V"         - Select 0.5V (coax) or 5V (optical) interface.
159	On some cards this doesn't work and you need to change the
160	configuration with hardware dip-switch.
161
162"IEC958 In Monitor" - SPDIF input is routed to DAC.
163
164"IEC958 In Phase Inverse" - Set SPDIF input format as inverse.
165	[FIXME: this doesn't work on all chips..]
166
167"IEC958 In Valid"   - Set input validity flag detection.
168
169Note: When "PCM Playback Switch" is on, you'll hear the digital output
170stream through analog line-out.
171
172
173The AC3 (RAW DIGITAL) OUTPUT
174----------------------------
175
176The driver supports raw digital (typically AC3) i/o over SPDIF.  This
177can be toggled via IEC958 playback control, but usually you need to
178access it via alsa-lib.  See alsa-lib documents for more details.
179
180On the raw digital mode, the "PCM Playback Switch" is automatically
181turned off so that non-audio data is heard from the analog line-out.
182Similarly the following switches are off: "IEC958 Mix Analog" and
183"IEC958 Loop".  The switches are resumed after closing the SPDIF PCM
184device automatically to the previous state.
185
186On the model 033, AC3 is implemented by the software conversion in
187the alsa-lib.  If you need to bypass the software conversion of IEC958
188subframes, pass the "soft_ac3=0" module option.  This doesn't matter
189on the newer models.
190
191
192ANALOG MIXER INTERFACE
193----------------------
194
195The mixer interface on CM8x38 is similar to SB16.
196There are Master, PCM, Synth, CD, Line, Mic and PC Speaker playback
197volumes.  Synth, CD, Line and Mic have playback and capture switches,
198too, as well as SB16.
199
200In addition to the standard SB mixer, CM8x38 provides more functions.
201- PCM playback switch
202- PCM capture switch (to capture the data sent to DAC)
203- Mic Boost switch
204- Mic capture volume
205- Aux playback volume/switch and capture switch
206- 3D control switch
207
208
209MIDI CONTROLLER
210---------------
211
212With CMI8338 chips, the MPU401-UART interface is disabled as default.
213You need to set the module option "mpu_port" to a valid I/O port address
214to enable MIDI support.  Valid I/O ports are 0x300, 0x310, 0x320 and
2150x330.  Choose a value that doesn't conflict with other cards.
216
217With CMI8738 and newer chips, the MIDI interface is enabled by default
218and the driver automatically chooses a port address.
219
220There is _no_ hardware wavetable function on this chip (except for
221OPL3 synth below).
222What's said as MIDI synth on Windows is a software synthesizer
223emulation.  On Linux use TiMidity or other softsynth program for
224playing MIDI music.
225
226
227FM OPL/3 Synth
228--------------
229
230The FM OPL/3 is also enabled as default only for the first card.
231Set "fm_port" module option for more cards.
232
233The output quality of FM OPL/3 is, however, very weird.
234I don't know why..
235
236CMI8768 and newer chips do not have the FM synth.
237
238
239Joystick and Modem
240------------------
241
242The legacy joystick is supported.  To enable the joystick support, pass
243joystick_port=1 module option.  The value 1 means the auto-detection.
244If the auto-detection fails, try to pass the exact I/O address.
245
246The modem is enabled dynamically via a card control switch "Modem".
247
248
249Debugging Information
250---------------------
251
252The registers are shown in /proc/asound/cardX/cmipci.  If you have any
253problem (especially unexpected behavior of mixer), please attach the
254output of this proc file together with the bug report.
255