| Brief Notes on C-Media 8338/8738/8768/8770 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 differences between the two DACs: | |
| - The first DAC supports U8 and S16LE formats, while the second DAC | |
| supports only S16LE. | |
| - The second 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 programming 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 switches affecting to the speaker connections: | |
| "Line-In Mode" - an enum control to change the behavior of line-in | |
| jack. Either "Line-In", "Rear Output" or "Bass Output" can | |
| be selected. The last item is available only with model 039 | |
| or newer. | |
| When "Rear Output" is chosen, the surround channels 3 and 4 | |
| are output to line-in jack. | |
| "Mic-In Mode" - an enum control to change the behavior of mic-in | |
| jack. Either "Mic-In" or "Center/LFE Output" can be | |
| selected. | |
| When "Center/LFE Output" is chosen, the center and bass | |
| channels (channels 5 and 6) are output to mic-in jack. | |
| Digital I/O | |
| ----------- | |
| The CM8x38 provides the excellent SPDIF capability with very cheap | |
| 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 ("IEC958" is the official name of | |
| so-called S/PDIF). 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 | |
| --------------- | |
| With CMI8338 chips, the MPU401-UART interface is disabled as default. | |
| You need to set the module option "mpu_port" to a valid I/O port address | |
| to enable MIDI support. Valid I/O ports are 0x300, 0x310, 0x320 and | |
| 0x330. Choose a value that doesn't conflict with other cards. | |
| With CMI8738 and newer chips, the MIDI interface is enabled by default | |
| and the driver automatically chooses a port address. | |
| 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.. | |
| CMI8768 and newer chips do not have the FM synth. | |
| Joystick and Modem | |
| ------------------ | |
| The legacy joystick is supported. To enable the joystick support, pass | |
| joystick_port=1 module option. The value 1 means the auto-detection. | |
| If the auto-detection fails, try to pass the exact I/O address. | |
| The modem is enabled dynamically via a card control switch "Modem". | |
| 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. |