/Documentation/sound/alsa/CMIPCI.txt
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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.