ALSA: emu10k1: add separate documentation for E-MU cards

They are sufficiently different from Sound Blasters.
Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230825222157.170978-3-oswald.buddenhagen@gmx.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

Documentation/sound/cards/emu-mixer.rst

+==================================================
+E-MU Digital Audio System mixer / default DSP code
+==================================================
+
+This document covers the E-MU 0404/1010/1212/1616/1820 PCI/PCI-e/CardBus
+cards.
+
+These cards use regular EMU10K2 (SoundBlaster Audigy) chips, but with an
+alternative front-end geared towards semi-professional studio recording.
+
+This document is based on audigy-mixer.rst.
+
+
+Hardware compatibility
+======================
+
+The EMU10K2 chips have a very short capture FIFO, which makes recording
+unreliable if the card's PCI bus requests are not handled with the
+appropriate priority.
+This is the case on more modern motherboards, where the PCI bus is only a
+secondary peripheral, rather than the actual arbiter of device access.
+In particular, I got recording glitches during simultaneous playback on an
+Intel DP55 board (memory controller in the CPU), but had success with an
+Intel DP45 board (memory controller in the north bridge).
+
+The PCI Express variants of these cards (which have a PCI bridge on board,
+but are otherwise identical) may be less problematic.
+
+
+Driver capabilities
+===================
+
+This driver supports only 16-bit 44.1/48 kHz operation. The multi-channel
+device (see emu10k1-jack.rst) additionally supports 24-bit capture.
+
+A patchset to enhance the driver is available from `a GitHub repository
+<https://github.com/ossilator/linux/tree/ossis-emu10k1>`_.
+Its multi-channel device supports 24-bit for both playback and capture,
+and also supports full 88.2/96/176.4/192 kHz operation.
+It is not going to be upstreamed due to a fundamental disagreement about
+what constitutes a good user experience.
+
+
+Digital mixer controls
+======================
+
+Note that the controls work as attenuators: the maximum value is the neutral
+position leaving the signal unchanged. Note that if the same destination is
+mentioned in multiple controls, the signal is accumulated and can be clipped
+(set to maximal or minimal value without checking for overflow).
+
+Explanation of used abbreviations:
+
+DAC
+	digital to analog converter
+ADC
+	analog to digital converter
+LFE
+	low frequency effects (used as subwoofer signal)
+IEC958
+	S/PDIF
+FX-bus
+	the EMU10K2 chip has an effect bus containing 64 accumulators.
+	Each of the synthesizer voices can feed its output to these accumulators
+	and the DSP microcontroller can operate with the resulting sum.
+
+name='Clock Source',index=0
+---------------------------
+This control allows switching the word clock between interally generated
+44.1 or 48 kHz, or a number of external sources.
+
+Note: the sources for the 1616 CardBus card are unclear. Please report your
+findings.
+
+name='Clock Fallback',index=0
+-----------------------------
+This control determines the internal clock which the card switches to when
+the selected external clock source is/becomes invalid.
+
+name='DAC1 0202 14dB PAD',index=0, etc.
+---------------------------------------
+Output attenuation controls. Not available on 0404 cards.
+
+name='ADC1 14dB PAD 0202',index=0, etc.
+---------------------------------------
+Input attenuation controls. Not available on 0404 cards.
+
+name='Optical Output Mode',index=0
+----------------------------------
+Switches the TOSLINK output port between S/PDIF and ADAT.
+Not available on 0404 cards (fixed to S/PDIF).
+
+name='Optical Input Mode',index=0
+---------------------------------
+Switches the TOSLINK input port between S/PDIF and ADAT.
+Not available on 0404 cards (fixed to S/PDIF).
+
+name='PCM Front Playback Volume',index=0
+----------------------------------------
+This control is used to attenuate samples from left and right front PCM FX-bus
+accumulators. ALSA uses accumulators 8 and 9 for left and right front PCM
+samples for 5.1 playback. The result samples are forwarded to the DSP 0 & 1
+playback channels.
+
+name='PCM Surround Playback Volume',index=0
+-------------------------------------------
+This control is used to attenuate samples from left and right surround PCM FX-bus
+accumulators. ALSA uses accumulators 2 and 3 for left and right surround PCM
+samples for 5.1 playback. The result samples are forwarded to the DSP 2 & 3
+playback channels.
+
+name='PCM Side Playback Volume',index=0
+---------------------------------------
+This control is used to attenuate samples from left and right side PCM FX-bus
+accumulators. ALSA uses accumulators 14 and 15 for left and right side PCM
+samples for 7.1 playback. The result samples are forwarded to the DSP 6 & 7
+playback channels.
+
+name='PCM Center Playback Volume',index=0
+-----------------------------------------
+This control is used to attenuate samples from the center PCM FX-bus accumulator.
+ALSA uses accumulator 6 for center PCM samples for 5.1 playback. The result samples
+are forwarded to the DSP 4 playback channel.
+
+name='PCM LFE Playback Volume',index=0
+--------------------------------------
+This control is used to attenuate samples from the LFE PCM FX-bus accumulator.
+ALSA uses accumulator 7 for LFE PCM samples for 5.1 playback. The result samples
+are forwarded to the DSP 5 playback channel.
+
+name='PCM Playback Volume',index=0
+----------------------------------
+This control is used to attenuate samples from left and right PCM FX-bus
+accumulators. ALSA uses accumulators 0 and 1 for left and right PCM samples for
+stereo playback. The result samples are forwarded to the virtual stereo mixer.
+
+name='PCM Capture Volume',index=0
+---------------------------------
+This control is used to attenuate samples from left and right PCM FX-bus
+accumulators. ALSA uses accumulators 0 and 1 for left and right PCM.
+The result is forwarded to the standard capture PCM device.
+
+name='Music Playback Volume',index=0
+------------------------------------
+This control is used to attenuate samples from left and right MIDI FX-bus
+accumulators. ALSA uses accumulators 4 and 5 for left and right MIDI samples.
+The result samples are forwarded to the virtual stereo mixer.
+
+name='Music Capture Volume',index=0
+-----------------------------------
+These controls are used to attenuate samples from left and right MIDI FX-bus
+accumulator. ALSA uses accumulators 4 and 5 for left and right MIDI samples.
+The result is forwarded to the standard capture PCM device.
+
+name='Front Playback Volume',index=0
+------------------------------------
+This control is used to attenuate samples from the virtual stereo mixer.
+The result samples are forwarded to the DSP 0 & 1 playback channels.
+
+name='Surround Playback Volume',index=0
+---------------------------------------
+This control is used to attenuate samples from the virtual stereo mixer.
+The result samples are forwarded to the DSP 2 & 3 playback channels.
+
+name='Side Playback Volume',index=0
+-----------------------------------
+This control is used to attenuate samples from the virtual stereo mixer.
+The result samples are forwarded to the DSP 6 & 7 playback channels.
+
+name='Center Playback Volume',index=0
+-------------------------------------
+This control is used to attenuate samples from the virtual stereo mixer.
+The result samples are forwarded to the DSP 4 playback channel.
+
+name='LFE Playback Volume',index=0
+----------------------------------
+This control is used to attenuate samples from the virtual stereo mixer.
+The result samples are forwarded to the DSP 5 playback channel.
+
+name='Tone Control - Switch',index=0
+------------------------------------
+This control turns the tone control on or off. The samples forwarded to
+the DSP playback channels are affected.
+
+name='Tone Control - Bass',index=0
+----------------------------------
+This control sets the bass intensity. There is no neutral value!!
+When the tone control code is activated, the samples are always modified.
+The closest value to pure signal is 20.
+
+name='Tone Control - Treble',index=0
+------------------------------------
+This control sets the treble intensity. There is no neutral value!!
+When the tone control code is activated, the samples are always modified.
+The closest value to pure signal is 20.
+
+name='Master Playback Volume',index=0
+-------------------------------------
+This control is used to attenuate samples for all DSP playback channels.
+
+name='EMU Capture Volume',index=0
+----------------------------------
+This control is used to attenuate samples from the DSP 0 & 1 capture channels.
+The result is forwarded to the standard capture PCM device.
+
+name='DAC Left',index=0, etc.
+-----------------------------
+Select the source for the given physical audio output. These may be physical
+inputs, playback channels (DSP xx, specified as a decimal number), or silence.
+
+name='DSP x',index=0
+--------------------
+Select the source for the given capture channel (specified as a hexadecimal
+digit). Same options as for the physical audio outputs.
+
+
+PCM stream related controls
+===========================
+
+These controls are described in audigy-mixer.rst.
+
+
+MANUALS/PATENTS
+===============
+
+See sb-live-mixer.rst.

Documentation/sound/cards/index.rst

@@ -8,6 +8,7 @@ Card-Specific Information
    cmipci
    sb-live-mixer
    audigy-mixer
+   emu-mixer
    emu10k1-jack
    via82xx-mixer
    audiophile-usb