/Documentation/sound/alsa/CMIPCI.txt

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