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PCM(4) BSD Kernel Interfaces Manual PCM(4) NAME pcm, snd -- FreeBSD PCM audio device infrastructure SYNOPSIS For a card with bridge driver support, and a PnP card: device pcm For a card without bridge driver support, and a non-PnP card, the follow- ing lines may be required in /boot/device.hints: hint.pcm.0.at="isa" hint.pcm.0.irq="5" hint.pcm.0.drq="1" hint.pcm.0.flags="0x0" DESCRIPTION The pcm driver provides support for PCM audio play and capture. This driver also supports various PCI, WSS/MSS compatible, ISA sound cards, and AC97 mixer. Once the pcm driver attaches, supported devices provide audio record and playback channels. The FreeBSD sound system provides dynamic mixing "VCHAN" and rate conversion "soft formats". True full du- plex operation is available on most cards. If the sound card is supported by a bridge driver, the pcm driver works in conjunction with the bridge driver. Apart from the usual parameters, the flags field is used to specify the secondary DMA channel (generally used for capture in full duplex cards). Flags are set to 0 for cards not using a secondary DMA channel, or to 0x10 + C to specify channel C. The driver works best with WSS/MSS cards, which have a very clean archi- tecture and an orthogonal set of features. They also happen to be among the cheapest audio cards on the market. The driver does its best to recognize the installed hardware and drive it correctly so the user is not required to add several lines in /boot/device.hints. For PCI and ISA PnP cards this is actually easy since they identify themselves. For legacy ISA cards, the driver looks for MSS cards at addresses 0x530 and 0x604 (unless overridden in /boot/device.hints). Boot Variables In general, the module snd_foo corresponds to device foo and can be loaded by the boot loader via boot/loader.conf or from the command line using the kldload(8) utility. Options which can be specified in /boot/loader.conf include: snd_driver_load ("NO") If set to "YES", this option loads all available drivers. snd_emu10k1_load ("NO") If set to "YES", Only the SoundBlaster 5.1 driver and dependent modules will be loaded. snd_foo_load ("NO") If set to "YES", load driver for card/chipset foo. VCHANS Each device can optionally support more playback channels that physical hardware provides by using "virtual channels" or VCHANs. VCHAN options can be configured via the sysctl(8) interface but can only be manipulated while the device is inactive. Runtime Configuration The following sysctl(8) tunables are available: hw.snd.pcm%d.buffersize Configure the amount of DMA bufferspace available for a device. hw.snd.targetirqrate Set the default block size such that continuous playback will achieve this IRQ rate. This value can be tuned to improve application performance. In- crease this value when the sound lags and decrease it if sound stutters or breaks up. hw.snd.unit When using devfs(5), the default device for /dev/dsp. Equivalent to a symlink from /dev/dsp to /dev/dsp${hw.snd.unit}. hw.snd.report_soft_formats Controls the internal format conversion if it is available transparently to the application software. When disabled or not available, the application will only be able to select formats the de- vice natively supports. hw.snd.verbose Level of verbosity for the /dev/sndstat device. Higher values include more output and the highest level, three, should be used when reported problems. Other options include: 0 - Installed devices and their allocated bus re- sources. 1 - The number of playback, record, virtual channels, and flags per device. 2 - Channel information per device including the channel's current format, speed, and pseudo device sta- tistics such as buffer overruns and buffer underruns. 3 - File names and versions of the currently sound loaded modules. hw.snd.maxautovchans Global VCHAN setting that only affects devices that have only one playback channel. The sound system will dynami- cally create up this many VCHANs. Set to "0" if no VCHANS are desired. hw.snd.pcm%d.vchans The current number of VCHANs allocated per device. This can be set to preal- locate a certain number of VCHANs. Setting this value to "0" will disable VCHANs for this device. Recording Channels On devices that have more than one recording source (ie: mic and line), there is a corresponding /dev/dspr%d.%d device. Statistics Channel statistics are only kept while the device is open. So with situ- ations involving overruns and underruns, consider the output while the errant application is open and running. IOCTL Support The driver supports most of the OSS ioctl() functions, and most applica- tions work unmodified. A few differences exist, while memory mapped playback is supported natively and in Linux emulation, memory mapped recording is not due to VM system design. As a consequence, some appli- cations may need to be recompiled with a slightly modified audio module. See <sys/soundcard.h> for a complete list of the supported ioctl() func- tions. SUPPORTED CARDS Below we include a list of supported codecs/cards. If your sound card is not listed here, it may be supported by a bridge driver. CS4237, CS4236, CS4232, CS4231 (ISA) All these cards work perfectly in full duplex using the MSS mode. This chipset is used, among others, on the A/Open AW35 and AW32, on some Intel motherboards, and (the CS4231) on some non-PnP cards. The CS4232 is reported as buggy in the Voxware documentation but I am not sure if this is true. On one of my Intel motherboards, capture does not work simply because the capture DMA channel is not wired to the ISA DMA controller. Yamaha OPL-SAx (ISA) Works perfectly in all modes. This chip is used in several PnP cards, but also (in non-PnP mode) on motherboards and laptops (e.g. the Toshiba Libretto). OPTi931 (ISA) The chip is buggy, but the driver has many workarounds to make it work in full duplex because for some time these were the only full duplex cards I could find. u-law formats uses U8 format internally because of a bug in the chip. Trident 4DWave DX/NX (PCI) ENSONIQ AudioPCI ES1370/1371 (PCI) Creative Labs SoundBlaster PCI is supported as well. ESS Solo-1/1E (PCI) NeoMagic 256AV/ZX (PCI) FILES The pcm drivers may create the following device nodes: /dev/audio%d.%d Sparc-compatible audio device. /dev/dsp%d.%d Digitized voice device. /dev/dspW%d.%d Like /dev/dsp, but 16 bits per sample. /dev/dspr%d.%d Should be connected to a record codec. /dev/sndstat Current pcm status, including all channels and driv- ers. The first number in the device node represents the unit number of the PCM device. All pcm PCM devices are listed in /dev/sndstat. Additional mes- sages are sometimes recorded when the device is probed and attached, these messages can be viewed with the dmesg(8) utility. DIAGNOSTICS ac97: dac not ready AC97 codec is not likely to be accompanied with the sound card. unsupported subdevice XX A device node is not created properly. BUGS Some features of your cards (e.g. global volume control) might not be supported on all devices. HISTORY The pcm device driver first appeared in FreeBSD 2.2.6 written by Luigi Rizzo. It was later rewritten in FreeBSD 4.0 by Cameron Grant. The API evolved from the VOXWARE standard which later became OSS standard. SEE ALSO csa(4), gusc(4), sbc(4), devfs(5), loader.conf(5), dmesg(8), kldload(8), sysctl(8) The OSS API, http://www.opensound.com/pguide/oss.pdf. AUTHORS Luigi Rizzo <luigi@iet.unipi.it> initially wrote the pcm device driver and this manual page. Cameron Grant <gandalf@vilnya.demon.co.uk> later revised the device driver for FreeBSD 4.0. Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp> revised this manual page. It was then rewritten for FreeBSD 5.2. BSD November 14, 2003 BSD
NAME | SYNOPSIS | DESCRIPTION | FILES | DIAGNOSTICS | BUGS | HISTORY | SEE ALSO | AUTHORS
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