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249 lines
8.9 KiB
249 lines
8.9 KiB
Brief Notes on C-Media 8738/8338 Driver
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=======================================
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Takashi Iwai <tiwai@suse.de>
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Front/Rear Multi-channel Playback
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---------------------------------
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CM8x38 chip can use ADC as the second DAC so that two different stereo
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channels can be used for front/rear playbacks. Since there are two
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DACs, both streams are handled independently unlike the 4/6ch multi-
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channel playbacks in the section below.
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As default, ALSA driver assigns the first PCM device (i.e. hw:0,0 for
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card#0) for front and 4/6ch playbacks, while the second PCM device
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(hw:0,1) is assigned to the second DAC for rear playback.
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There are slight difference between two DACs.
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- The first DAC supports U8 and S16LE formats, while the second DAC
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supports only S16LE.
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- The seconde DAC supports only two channel stereo.
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Please note that the CM8x38 DAC doesn't support continuous playback
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rate but only fixed rates: 5512, 8000, 11025, 16000, 22050, 32000,
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44100 and 48000 Hz.
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The rear output can be heard only when "Four Channel Mode" switch is
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disabled. Otherwise no signal will be routed to the rear speakers.
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As default it's turned on.
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*** WARNING ***
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When "Four Channel Mode" switch is off, the output from rear speakers
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will be FULL VOLUME regardless of Master and PCM volumes.
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This might damage your audio equipment. Please disconnect speakers
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before your turn off this switch.
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*** WARNING ***
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[ Well.. I once got the output with correct volume (i.e. same with the
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front one) and was so excited. It was even with "Four Channel" bit
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on and "double DAC" mode. Actually I could hear separate 4 channels
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from front and rear speakers! But.. after reboot, all was gone.
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It's a very pity that I didn't save the register dump at that
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time.. Maybe there is an unknown register to achieve this... ]
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If your card has an extra output jack for the rear output, the rear
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playback should be routed there as default. If not, there is a
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control switch in the driver "Line-In As Rear", which you can change
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via alsamixer or somewhat else. When this switch is on, line-in jack
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is used as rear output.
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There are two more controls regarding to the rear output.
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The "Exchange DAC" switch is used to exchange front and rear playback
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routes, i.e. the 2nd DAC is output from front output.
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4/6 Multi-Channel Playback
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--------------------------
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The recent CM8738 chips support for the 4/6 multi-channel playback
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function. This is useful especially for AC3 decoding.
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When the multi-channel is supported, the driver name has a suffix
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"-MC" such like "CMI8738-MC6". You can check this name from
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/proc/asound/cards.
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When the 4/6-ch output is enabled, the second DAC accepts up to 6 (or
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4) channels. While the dual DAC supports two different rates or
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formats, the 4/6-ch playback supports only the same condition for all
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channels. Since the multi-channel playback mode uses both DACs, you
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cannot operate with full-duplex.
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The 4.0 and 5.1 modes are defined as the pcm "surround40" and "surround51"
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in alsa-lib. For example, you can play a WAV file with 6 channels like
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% aplay -Dsurround51 sixchannels.wav
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For programmin the 4/6 channel playback, you need to specify the PCM
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channels as you like and set the format S16LE. For example, for playback
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with 4 channels,
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snd_pcm_hw_params_set_access(pcm, hw, SND_PCM_ACCESS_RW_INTERLEAVED);
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// or mmap if you like
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snd_pcm_hw_params_set_format(pcm, hw, SND_PCM_FORMAT_S16_LE);
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snd_pcm_hw_params_set_channels(pcm, hw, 4);
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and use the interleaved 4 channel data.
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There are some control switchs affecting to the speaker connections:
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"Line-In Mode" - an enum control to change the behavior of line-in
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jack. Either "Line-In", "Rear Output" or "Bass Output" can
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be selected. The last item is available only with model 039
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or newer.
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When "Rear Output" is chosen, the surround channels 3 and 4
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are output to line-in jack.
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"Mic-In Mode" - an enum control to change the behavior of mic-in
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jack. Either "Mic-In" or "Center/LFE Output" can be
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selected.
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When "Center/LFE Output" is chosen, the center and bass
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channels (channels 5 and 6) are output to mic-in jack.
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Digital I/O
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-----------
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The CM8x38 provides the excellent SPDIF capability with very cheap
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price (yes, that's the reason I bought the card :)
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The SPDIF playback and capture are done via the third PCM device
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(hw:0,2). Usually this is assigned to the PCM device "spdif".
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The available rates are 44100 and 48000 Hz.
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For playback with aplay, you can run like below:
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% aplay -Dhw:0,2 foo.wav
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or
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% aplay -Dspdif foo.wav
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24bit format is also supported experimentally.
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The playback and capture over SPDIF use normal DAC and ADC,
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respectively, so you cannot playback both analog and digital streams
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simultaneously.
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To enable SPDIF output, you need to turn on "IEC958 Output Switch"
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control via mixer or alsactl ("IEC958" is the official name of
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so-called S/PDIF). Then you'll see the red light on from the card so
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you know that's working obviously :)
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The SPDIF input is always enabled, so you can hear SPDIF input data
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from line-out with "IEC958 In Monitor" switch at any time (see
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below).
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You can play via SPDIF even with the first device (hw:0,0),
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but SPDIF is enabled only when the proper format (S16LE), sample rate
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(441100 or 48000) and channels (2) are used. Otherwise it's turned
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off. (Also don't forget to turn on "IEC958 Output Switch", too.)
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Additionally there are relevant control switches:
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"IEC958 Mix Analog" - Mix analog PCM playback and FM-OPL/3 streams and
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output through SPDIF. This switch appears only on old chip
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models (CM8738 033 and 037).
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Note: without this control you can output PCM to SPDIF.
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This is "mixing" of streams, so e.g. it's not for AC3 output
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(see the next section).
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"IEC958 In Select" - Select SPDIF input, the internal CD-in (false)
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and the external input (true).
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"IEC958 Loop" - SPDIF input data is loop back into SPDIF
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output (aka bypass)
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"IEC958 Copyright" - Set the copyright bit.
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"IEC958 5V" - Select 0.5V (coax) or 5V (optical) interface.
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On some cards this doesn't work and you need to change the
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configuration with hardware dip-switch.
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"IEC958 In Monitor" - SPDIF input is routed to DAC.
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"IEC958 In Phase Inverse" - Set SPDIF input format as inverse.
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[FIXME: this doesn't work on all chips..]
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"IEC958 In Valid" - Set input validity flag detection.
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Note: When "PCM Playback Switch" is on, you'll hear the digital output
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stream through analog line-out.
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The AC3 (RAW DIGITAL) OUTPUT
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----------------------------
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The driver supports raw digital (typically AC3) i/o over SPDIF. This
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can be toggled via IEC958 playback control, but usually you need to
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access it via alsa-lib. See alsa-lib documents for more details.
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On the raw digital mode, the "PCM Playback Switch" is automatically
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turned off so that non-audio data is heard from the analog line-out.
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Similarly the following switches are off: "IEC958 Mix Analog" and
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"IEC958 Loop". The switches are resumed after closing the SPDIF PCM
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device automatically to the previous state.
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On the model 033, AC3 is implemented by the software conversion in
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the alsa-lib. If you need to bypass the software conversion of IEC958
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subframes, pass the "soft_ac3=0" module option. This doesn't matter
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on the newer models.
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ANALOG MIXER INTERFACE
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----------------------
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The mixer interface on CM8x38 is similar to SB16.
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There are Master, PCM, Synth, CD, Line, Mic and PC Speaker playback
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volumes. Synth, CD, Line and Mic have playback and capture switches,
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too, as well as SB16.
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In addition to the standard SB mixer, CM8x38 provides more functions.
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- PCM playback switch
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- PCM capture switch (to capture the data sent to DAC)
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- Mic Boost switch
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- Mic capture volume
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- Aux playback volume/switch and capture switch
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- 3D control switch
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MIDI CONTROLLER
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---------------
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The MPU401-UART interface is disabled as default. You need to set
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module option "mpu_port" with a valid I/O port address to enable the
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MIDI support. The valid I/O ports are 0x300, 0x310, 0x320 and 0x330.
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Choose the value which doesn't conflict with other cards.
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There is _no_ hardware wavetable function on this chip (except for
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OPL3 synth below).
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What's said as MIDI synth on Windows is a software synthesizer
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emulation. On Linux use TiMidity or other softsynth program for
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playing MIDI music.
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FM OPL/3 Synth
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--------------
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The FM OPL/3 is also enabled as default only for the first card.
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Set "fm_port" module option for more cards.
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The output quality of FM OPL/3 is, however, very weird.
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I don't know why..
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Joystick and Modem
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------------------
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The legacy joystick is supported. To enable the joystick support, pass
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joystick_port=1 module option. The value 1 means the auto-detection.
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If the auto-detection fails, try to pass the exact I/O address.
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The modem is enabled dynamically via a card control switch "Modem".
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Debugging Information
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---------------------
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The registers are shown in /proc/asound/cardX/cmipci. If you have any
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problem (especially unexpected behavior of mixer), please attach the
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output of this proc file together with the bug report.
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