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diff --git a/Documentation/sound/oss/vwsnd b/Documentation/sound/oss/vwsnd new file mode 100644 index 0000000..a6ea0a1 --- /dev/null +++ b/Documentation/sound/oss/vwsnd @@ -0,0 +1,293 @@ +vwsnd - Sound driver for the Silicon Graphics 320 and 540 Visual +Workstations' onboard audio. + +Copyright 1999 Silicon Graphics, Inc. All rights reserved. + + +At the time of this writing, March 1999, there are two models of +Visual Workstation, the 320 and the 540. This document only describes +those models. Future Visual Workstation models may have different +sound capabilities, and this driver will probably not work on those +boxes. + +The Visual Workstation has an Analog Devices AD1843 "SoundComm" audio +codec chip. The AD1843 is accessed through the Cobalt I/O ASIC, also +known as Lithium. This driver programs both both chips. + +============================================================================== +QUICK CONFIGURATION + + # insmod soundcore + # insmod vwsnd + +============================================================================== +I/O CONNECTIONS + +On the Visual Workstation, only three of the AD1843 inputs are hooked +up. The analog line in jacks are connected to the AD1843's AUX1 +input. The CD audio lines are connected to the AD1843's AUX2 input. +The microphone jack is connected to the AD1843's MIC input. The mic +jack is mono, but the signal is delivered to both the left and right +MIC inputs. You can record in stereo from the mic input, but you will +get the same signal on both channels (within the limits of A/D +accuracy). Full scale on the Line input is +/- 2.0 V. Full scale on +the MIC input is 20 dB less, or +/- 0.2 V. + +The AD1843's LOUT1 outputs are connected to the Line Out jacks. The +AD1843's HPOUT outputs are connected to the speaker/headphone jack. +LOUT2 is not connected. Line out's maximum level is +/- 2.0 V peak to +peak. The speaker/headphone out's maximum is +/- 4.0 V peak to peak. + +The AD1843's PCM input channel and one of its output channels (DAC1) +are connected to Lithium. The other output channel (DAC2) is not +connected. + +============================================================================== +CAPABILITIES + +The AD1843 has PCM input and output (Pulse Code Modulation, also known +as wavetable). PCM input and output can be mono or stereo in any of +four formats. The formats are 16 bit signed and 8 bit unsigned, +u-Law, and A-Law format. Any sample rate from 4 KHz to 49 KHz is +available, in 1 Hz increments. + +The AD1843 includes an analog mixer that can mix all three input +signals (line, mic and CD) into the analog outputs. The mixer has a +separate gain control and mute switch for each input. + +There are two outputs, line out and speaker/headphone out. They +always produce the same signal, and the speaker always has 3 dB more +gain than the line out. The speaker/headphone output can be muted, +but this driver does not export that function. + +The hardware can sync audio to the video clock, but this driver does +not have a way to specify syncing to video. + +============================================================================== +PROGRAMMING + +This section explains the API supported by the driver. Also see the +Open Sound Programming Guide at http://www.opensound.com/pguide/ . +This section assumes familiarity with that document. + +The driver has two interfaces, an I/O interface and a mixer interface. +There is no MIDI or sequencer capability. + +============================================================================== +PROGRAMMING PCM I/O + +The I/O interface is usually accessed as /dev/audio or /dev/dsp. +Using the standard Open Sound System (OSS) ioctl calls, the sample +rate, number of channels, and sample format may be set within the +limitations described above. The driver supports triggering. It also +supports getting the input and output pointers with one-sample +accuracy. + +The SNDCTL_DSP_GETCAP ioctl returns these capabilities. + + DSP_CAP_DUPLEX - driver supports full duplex. + + DSP_CAP_TRIGGER - driver supports triggering. + + DSP_CAP_REALTIME - values returned by SNDCTL_DSP_GETIPTR + and SNDCTL_DSP_GETOPTR are accurate to a few samples. + +Memory mapping (mmap) is not implemented. + +The driver permits subdivided fragment sizes from 64 to 4096 bytes. +The number of fragments can be anything from 3 fragments to however +many fragments fit into 124 kilobytes. It is up to the user to +determine how few/small fragments can be used without introducing +glitches with a given workload. Linux is not realtime, so we can't +promise anything. (sigh...) + +When this driver is switched into or out of mu-Law or A-Law mode on +output, it may produce an audible click. This is unavoidable. To +prevent clicking, use signed 16-bit mode instead, and convert from +mu-Law or A-Law format in software. + +============================================================================== +PROGRAMMING THE MIXER INTERFACE + +The mixer interface is usually accessed as /dev/mixer. It is accessed +through ioctls. The mixer allows the application to control gain or +mute several audio signal paths, and also allows selection of the +recording source. + +Each of the constants described here can be read using the +MIXER_READ(SOUND_MIXER_xxx) ioctl. Those that are not read-only can +also be written using the MIXER_WRITE(SOUND_MIXER_xxx) ioctl. In most +cases, <sys/soundcard.h> defines constants SOUND_MIXER_READ_xxx and +SOUND_MIXER_WRITE_xxx which work just as well. + +SOUND_MIXER_CAPS Read-only + +This is a mask of optional driver capabilities that are implemented. +This driver's only capability is SOUND_CAP_EXCL_INPUT, which means +that only one recording source can be active at a time. + +SOUND_MIXER_DEVMASK Read-only + +This is a mask of the sound channels. This driver's channels are PCM, +LINE, MIC, CD, and RECLEV. + +SOUND_MIXER_STEREODEVS Read-only + +This is a mask of which sound channels are capable of stereo. All +channels are capable of stereo. (But see caveat on MIC input in I/O +CONNECTIONS section above). + +SOUND_MIXER_OUTMASK Read-only + +This is a mask of channels that route inputs through to outputs. +Those are LINE, MIC, and CD. + +SOUND_MIXER_RECMASK Read-only + +This is a mask of channels that can be recording sources. Those are +PCM, LINE, MIC, CD. + +SOUND_MIXER_PCM Default: 0x5757 (0 dB) + +This is the gain control for PCM output. The left and right channel +gain are controlled independently. This gain control has 64 levels, +which range from -82.5 dB to +12.0 dB in 1.5 dB steps. Those 64 +levels are mapped onto 100 levels at the ioctl, see below. + +SOUND_MIXER_LINE Default: 0x4a4a (0 dB) + +This is the gain control for mixing the Line In source into the +outputs. The left and right channel gain are controlled +independently. This gain control has 32 levels, which range from +-34.5 dB to +12.0 dB in 1.5 dB steps. Those 32 levels are mapped onto +100 levels at the ioctl, see below. + +SOUND_MIXER_MIC Default: 0x4a4a (0 dB) + +This is the gain control for mixing the MIC source into the outputs. +The left and right channel gain are controlled independently. This +gain control has 32 levels, which range from -34.5 dB to +12.0 dB in +1.5 dB steps. Those 32 levels are mapped onto 100 levels at the +ioctl, see below. + +SOUND_MIXER_CD Default: 0x4a4a (0 dB) + +This is the gain control for mixing the CD audio source into the +outputs. The left and right channel gain are controlled +independently. This gain control has 32 levels, which range from +-34.5 dB to +12.0 dB in 1.5 dB steps. Those 32 levels are mapped onto +100 levels at the ioctl, see below. + +SOUND_MIXER_RECLEV Default: 0 (0 dB) + +This is the gain control for PCM input (RECording LEVel). The left +and right channel gain are controlled independently. This gain +control has 16 levels, which range from 0 dB to +22.5 dB in 1.5 dB +steps. Those 16 levels are mapped onto 100 levels at the ioctl, see +below. + +SOUND_MIXER_RECSRC Default: SOUND_MASK_LINE + +This is a mask of currently selected PCM input sources (RECording +SouRCes). Because the AD1843 can only have a single recording source +at a time, only one bit at a time can be set in this mask. The +allowable values are SOUND_MASK_PCM, SOUND_MASK_LINE, SOUND_MASK_MIC, +or SOUND_MASK_CD. Selecting SOUND_MASK_PCM sets up internal +resampling which is useful for loopback testing and for hardware +sample rate conversion. But software sample rate conversion is +probably faster, so I don't know how useful that is. + +SOUND_MIXER_OUTSRC DEFAULT: SOUND_MASK_LINE|SOUND_MASK_MIC|SOUND_MASK_CD + +This is a mask of sources that are currently passed through to the +outputs. Those sources whose bits are not set are muted. + +============================================================================== +GAIN CONTROL + +There are five gain controls listed above. Each has 16, 32, or 64 +steps. Each control has 1.5 dB of gain per step. Each control is +stereo. + +The OSS defines the argument to a channel gain ioctl as having two +components, left and right, each of which ranges from 0 to 100. The +two components are packed into the same word, with the left side gain +in the least significant byte, and the right side gain in the second +least significant byte. In C, we would say this. + + #include <assert.h> + + ... + + assert(leftgain >= 0 && leftgain <= 100); + assert(rightgain >= 0 && rightgain <= 100); + arg = leftgain | rightgain << 8; + +So each OSS gain control has 101 steps. But the hardware has 16, 32, +or 64 steps. The hardware steps are spread across the 101 OSS steps +nearly evenly. The conversion formulas are like this, given N equals +16, 32, or 64. + + int round = N/2 - 1; + OSS_gain_steps = (hw_gain_steps * 100 + round) / (N - 1); + hw_gain_steps = (OSS_gain_steps * (N - 1) + round) / 100; + +Here is a snippet of C code that will return the left and right gain +of any channel in dB. Pass it one of the predefined gain_desc_t +structures to access any of the five channels' gains. + + typedef struct gain_desc { + float min_gain; + float gain_step; + int nbits; + int chan; + } gain_desc_t; + + const gain_desc_t gain_pcm = { -82.5, 1.5, 6, SOUND_MIXER_PCM }; + const gain_desc_t gain_line = { -34.5, 1.5, 5, SOUND_MIXER_LINE }; + const gain_desc_t gain_mic = { -34.5, 1.5, 5, SOUND_MIXER_MIC }; + const gain_desc_t gain_cd = { -34.5, 1.5, 5, SOUND_MIXER_CD }; + const gain_desc_t gain_reclev = { 0.0, 1.5, 4, SOUND_MIXER_RECLEV }; + + int get_gain_dB(int fd, const gain_desc_t *gp, + float *left, float *right) + { + int word; + int lg, rg; + int mask = (1 << gp->nbits) - 1; + + if (ioctl(fd, MIXER_READ(gp->chan), &word) != 0) + return -1; /* fail */ + lg = word & 0xFF; + rg = word >> 8 & 0xFF; + lg = (lg * mask + mask / 2) / 100; + rg = (rg * mask + mask / 2) / 100; + *left = gp->min_gain + gp->gain_step * lg; + *right = gp->min_gain + gp->gain_step * rg; + return 0; + } + +And here is the corresponding routine to set a channel's gain in dB. + + int set_gain_dB(int fd, const gain_desc_t *gp, float left, float right) + { + float max_gain = + gp->min_gain + (1 << gp->nbits) * gp->gain_step; + float round = gp->gain_step / 2; + int mask = (1 << gp->nbits) - 1; + int word; + int lg, rg; + + if (left < gp->min_gain || right < gp->min_gain) + return EINVAL; + lg = (left - gp->min_gain + round) / gp->gain_step; + rg = (right - gp->min_gain + round) / gp->gain_step; + if (lg >= (1 << gp->nbits) || rg >= (1 << gp->nbits)) + return EINVAL; + lg = (100 * lg + mask / 2) / mask; + rg = (100 * rg + mask / 2) / mask; + word = lg | rg << 8; + + return ioctl(fd, MIXER_WRITE(gp->chan), &word); + } + |
