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SND_HDA(4) Device Drivers Manual SND_HDA(4)


snd_hdaIntel High Definition Audio bridge device driver


To compile this driver into the kernel, place the following lines in your kernel configuration file:
device sound
device snd_hda
Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):


The High Definition (HD) Audio specification was developed by Intel as the logical successor of the old AC'97 specification and has several advantages, such as higher bandwidth which allows more channels and more detailed formats, support for several logical audio devices, and general purpose DMA channels.
The snd_hda driver is a HDA bus controller driver and HDA codecs audio functions bridge driver that allows the generic audio driver, sound(4), to be used with this hardware. Only audio functions are supported by snd_hda. Modem and other possible functions are not implemented.
The snd_hda driver supports hardware that conforms with revision 1.0 of the Intel High Definition Audio specification and tries to behave much like the Microsoft Universal Audio Architecture (UAA) draft (revision 0.7b) for handling audio devices.
According to HDA and UAA specifications, depending on the number of HDA buses and codecs present in system, their audio capabilities and BIOS provided configuration, the snd_hda driver often provides several PCM audio devices. For example, one device for main rear 7.1 output and inputs, one device for independent headset connectors at front and one device for SPDIF or HDMI audio input/output. The assignment of audio inputs and outputs may be tuned with device.hints(5). The driver's verbose boot messages provide a lot of information about the operation of the driver and present audio setup.
The default audio device may be tuned by setting the hw.snd.default_unit sysctl, as described in sound(4), or explicitly specified in application settings.

Boot-time Configuration

The following variables are available at boot-time through the device.hints(5) file:
Configures a range of possible options. Possible values are: “dmapos”, “eapdinv”, “gpio0”, “gpio1”, “gpio2”, “gpio3”, “gpio4”, “gpio5”, “gpio6”, “gpio7”, “gpioflush”, “ivref”, “ivref50”, “ivref80”, “ivref100”, “fixedrate”, “forcestereo”, “ovref”, “ovref50”, “ovref80”, “ovref100”, “senseinv”, “softpcmvol”, and “vref”. An option prefixed with “no”, such as “nofixedrate”, will do the opposite and takes precedence. Options can be separated by whitespace and commas.
GPIOs” are a codec's General Purpose I/O pins which system integrators sometimes use to control external muters, amplifiers and so on. If you have no sound, or sound volume is not adequate, you may have to experiment a bit with the GPIO setup to find the optimal setup for your system.
The “ivrefX” and “ovrefX” options control the voltage used to power external microphones.
Controls MSI (Message Signaled Interrupts) support.
Overrides codec pin configuration set by BIOS. May be specified as a 32-bit hexadecimal value with a leading “0x”, or as a set of space-separated “option=value” pairs.
Pin configuration is the UAA driver's main source of information about codec usage. This information is usually provided by the codec manufacturer and tuned by system integrators for specific system requirements. The snd_hda driver allows users to override it to fix integrator mistakes or to use the available codec in alternative ways (for example to get stereo output and 2 inputs instead of a single 5.1 output).
The following options are supported:
Association number. Associations are used to group individual pins to form a complex multi-pin device. For example, to group 4 connectors for 7.1 output, or to treat several input connectors as sources for the same input device. Association numbers can be specified as numeric values from 0 to 15. A value of 0 means disabled pin. A value of 15 is a set of independent unassociated pins. Each association includes only pins of the same direction (in/out) and is detected atomically (all pins or none). A separate PCM audio device is created for every pair of input and output associations.
Sequence number. A unique, per-association number used to order pins inside the particular association. Sequence numbers can be specified as numeric values from 0 to 15.
For output assotiations sequence numbers encode speaker pairs positions: 0 - Front, 1 - Center/LFE, 2 - Back, 3 - Front Wide Center, 4 - Side. Standard combinations are: (0) - Stereo; (0, 2), (0, 4) - Quadro; (0, 1, 2), (0, 1, 4) - 5.1; (0, 1, 2, 4) - 7.1.
The sequence number 15 has a special meaning for output associations. Output pins with this number and device type “Headphones” will duplicate (with automatic mute if jack detection is supported) the first pin in that association.
Device type. Can be specified as a number from 0 to 15 or as a name: “Line-out”, “Speaker”, “Headphones,” “CD”, “SPDIF-out”, “Digital-out”, “Modem-line”, “Modem-handset”, “Line-in”, “AUX”, “Mic”, “Telephony”, “SPDIF-in”, “Digital-in”, “Res.E”, or “Other”. The device type also describes the pin direction (in/out). For example, “CD” always means an input pin, while “Headphones” always means an output.
Connection type. Can be specified as a number from 0 to 3. The connection type can also be specified as one of the special names “Jack”, “None”, “Fixed”, or “Both”. Pins with a connection type of “None” are disabled.
Connector physical type. Can be specified as a number from 0 to 15. This is a reference only value. It is ignored by the snd_hda driver.
Connector color. Can be specified as a number from 0 to 15 or as one of the names “Unknown”, “Black”, “Grey”, “Blue”, “Green”, “Red”, “Orange”, “Yellow”, “Purple”, “Pink”, “Res.A”, “Res.B”, “Res.C”, “Res.D”, “White”, or “Other”. This is a reference only value. It is ignored by the snd_hda driver.
Connector physical location. Can be specified as a number from 0 to 63. This is a reference only value. It is ignored by the snd_hda driver.
Misc bits. Can be specified as a number from 0 to 15. Bit 0 has a special meaning. When set it means that jack detection is not implemented in hardware.

Runtime Configuration

The following sysctl(8) variables are available in addition to those available to all sound(4) devices:
Enables polling mode. In this mode the driver operates by querying the device state on timer ticks using callout(9) instead of interrupts. Polling is disabled by default. Do not enable it unless you are facing weird interrupt problems or if the device cannot generate interrupts at all.
Controller/Jack Sense polling interval (1-1000 ms)
Setting this to a non-zero value dumps the current pin configuration, main capabilities and jack sense status to console and syslog.


Taking HP Compaq DX2300 with Realtek ALC888 HDA codec for example. This system has two audio connectors on a front side, three audio connectors on a rear side and one internal speaker. According to verbose driver output and the codec datasheet, this codec has five stereo DACs and two stereo ADCs, all of them are routable to any codec pin (external connector). All codec pins are reversible (could be configured either as input or output).
So high codec uniformity and flexibility allow driver to configure it in many different ways, depending on requested pins usage decribed by pins configuration. The driver reports such default pin configuration when verbose messages enabled:
hdac0: nid 20 0x01014020 as  2 seq  0   Line-out  Jack jack 1 loc  1 color   Green misc 0 
hdac0: nid 21 0x99130110 as  1 seq  0    Speaker Fixed jack 3 loc 25 color Unknown misc 1 
hdac0: nid 22 0x411111f0 as 15 seq  0    Speaker  None jack 1 loc  1 color   Black misc 1 
hdac0: nid 23 0x411111f0 as 15 seq  0    Speaker  None jack 1 loc  1 color   Black misc 1 
hdac0: nid 24 0x01a19830 as  3 seq  0        Mic  Jack jack 1 loc  1 color    Pink misc 8 
hdac0: nid 25 0x02a1983f as  3 seq 15        Mic  Jack jack 1 loc  2 color    Pink misc 8 
hdac0: nid 26 0x01813031 as  3 seq  1    Line-in  Jack jack 1 loc  1 color    Blue misc 0 
hdac0: nid 27 0x0221401f as  1 seq 15 Headphones  Jack jack 1 loc  2 color   Green misc 0 
hdac0: nid 28 0x411111f0 as 15 seq  0    Speaker  None jack 1 loc  1 color   Black misc 1 
hdac0: nid 30 0x411111f0 as 15 seq  0    Speaker  None jack 1 loc  1 color   Black misc 1 
hdac0: nid 31 0x411111f0 as 15 seq  0    Speaker  None jack 1 loc  1 color   Black misc 1
Here we can see, that the nodes with ID (nid) 25 and 27 are front panel connectors (Jack, loc 2), nids 20, 24 and 26 are rear panel connectors (Jack, loc 1) and nid 21 is a built-in speaker (Fixed, loc 25). Pins with nids 22, 23, 28, 30 and 31 will be disabled by driver due to "None" connectivity. So the pin count and description matches to connectors that we have.
Using association (as) and sequence (seq) fields values pins are grouped into 3 associations:
hdac0: Association 0 (1) out: 
hdac0:   Pin nid=21 seq=0 
hdac0:   Pin nid=27 seq=15 
hdac0: Association 1 (2) out: 
hdac0:   Pin nid=20 seq=0 
hdac0: Association 2 (3) in: 
hdac0:   Pin nid=24 seq=0 
hdac0:   Pin nid=26 seq=1 
hdac0:   Pin nid=25 seq=15
Each pcm(4) device uses two associations: one for playback and one for recording. Associations processed and assigned to pcm(4) devices in increasing numerical order. In this case association #0 (1) will become pcm0 device playback, using the internal speakers and Headphones jack with speaker automute on the headphones jack connection. Association #1 (2) will become pcm1 playback, using the Line-out jack. Association #2 (3) will become pcm0 recording, using the external microphones and the Line-in jack.
The snd_hda driver provides extensive verbose messages to diagnose its operation logic and describe its current codec configuration.
Using device.hints(5) it is possible to modify the configuration of the existing pins, allowing a broad range of different audio setups. Here are a few examples of some setups possible for this particular hardware:

Example 1

Setting the device.hints(5) options
will swap line-out and speaker functions. So the pcm0 device will play to the line-out and headphones jacks. Line-out will be muted on the headphones jack connection. Recording on pcm0 will go from two external microphones and line-in jacks. pcm1 playback will go to the internal speaker.

Example 2

Setting the device.hints(5) options
hint.hdac.0.cad0.nid20.config="as=1 seq=15 device=Headphones" 
hint.hdac.0.cad0.nid27.config="as=2 seq=0" 
hint.hdac.0.cad0.nid25.config="as=4 seq=0"
will split the headphones and one of the microphones to a separate device. The pcm0 device will play to the internal speaker and to the line-out jack, with speaker automute on the line-out jack connection. Recording on pcm0 will use input from one external microphone and the line-in jacks. The pcm1 device will be completely dedicated to a headset (headphones and mic) connected to the front connectors.

Example 3

Setting the device.hints(5) options
hint.hdac.0.cad0.nid20.config="as=1 seq=0" 
hint.hdac.0.cad0.nid26.config="as=2 seq=0" 
hint.hdac.0.cad0.nid27.config="as=3 seq=0" 
hint.hdac.0.cad0.nid25.config="as=4 seq=0" 
hint.hdac.0.cad0.nid24.config="as=5 seq=0 device=Line-out" 
hint.hdac.0.cad0.nid21.config="as=6 seq=0"
will give 4 independent devices: pcm0 (line-out and line-in), pcm1 (headphones and mic), pcm2 (additional line-out via retasked rear mic jack), and pcm3 (internal speaker).

Example 4

Setting the device.hints(5) options
hint.hdac.0.cad0.nid20.config="as=1 seq=0" 
hint.hdac.0.cad0.nid24.config="as=1 seq=1 device=Line-out" 
hint.hdac.0.cad0.nid26.config="as=1 seq=2 device=Line-out" 
hint.hdac.0.cad0.nid21.config="as=2 seq=0"
will give 2 devices: pcm0 for 5.1 playback via 3 rear connectors (line-out and retasked mic and line-in) and headset (headphones and mic) at front connectors. pcm1 for internal speaker playback. On headphones connection rear connectors will be muted.


Depending on codec configuration, these controls and signal sources could be reported to sound(4):
overall output level (volume)
overall recording level
input-to-output monitoring loopback level
external amplifier control
PCM playback
input mix
first external or second internal microphone input
first internal or second external microphone input
line, line1, line2, line3
analog (line) inputs
dig1, dig2, dig3
digital (S/PDIF, HDMI or DisplayPort) inputs
CD input
PC speaker input
phin, phout, radio. video
other random inputs
Controls have different precision. Some could be just an on/off triggers. Most of controls use logarithmic scale.


The snd_hda driver supports many Intel HDA compatible audio chipsets including the following:
  • ATI SB450
  • ATI SB600
  • Intel 631x/632xESB
  • Intel 82801F (ICH6)
  • Intel 82801G (ICH7)
  • Intel 82801H (ICH8)
  • Intel 82801I (ICH9)
  • Intel 82801J (ICH10)
  • Intel US15W (SCH)
  • nVidia MCP51
  • nVidia MCP55
  • nVidia MCP61A
  • nVidia MCP61B
  • nVidia MCP63
  • nVidia MCP65A
  • nVidia MCP65B
  • nVidia MCP67A
  • nVidia MCP67B
  • nVidia MCP68
  • nVidia MCP69
  • nVidia MCP73
  • nVidia MCP78
  • nVidia MCP79
  • nVidia MCP89
  • SiS 966
  • VIA VT8251/8237A
The following and many other codecs have been verified to work:
  • Analog Devices AD1981HD
  • Analog Devices AD1983
  • Analog Devices AD1984
  • Analog Devices AD1986A
  • Analog Devices AD1988
  • Analog Devices AD1988B
  • CMedia CMI9880
  • Conexant CX20549 (Venice)
  • Conexant CX20551 (Waikiki)
  • Conexant CX20561 (Hermosa)
  • Realtek ALC260
  • Realtek ALC262
  • Realtek ALC268
  • Realtek ALC660
  • Realtek ALC861
  • Realtek ALC861VD
  • Realtek ALC880
  • Realtek ALC882
  • Realtek ALC883
  • Realtek ALC885
  • Realtek ALC888
  • Realtek ALC889
  • Sigmatel STAC9205
  • Sigmatel STAC9220
  • Sigmatel STAC9220D / 9223D
  • Sigmatel STAC9221
  • Sigmatel STAC9221D
  • Sigmatel STAC9227D
  • Sigmatel STAC9227X
  • Sigmatel STAC9228D
  • Sigmatel STAC9228X
  • Sigmatel STAC9229D
  • Sigmatel STAC9229X
  • Sigmatel STAC9230D
  • Sigmatel STAC9230X
  • Sigmatel STAC9271D
  • Sigmatel STAC9872AK
  • VIA VT1708
  • VIA VT1708B
  • VIA VT1709


sound(4), snd_ich(4), device.hints(5), loader.conf(5), sysctl(8)


The snd_hda device driver first appeared in FreeBSD 6.3.


The snd_hda driver was written by Stephane E. Potvin ⟨⟩, Ariff Abdullah ⟨⟩ and Alexander Motin ⟨⟩. This manual page was written by Joel Dahl ⟨⟩, Alexander Motin ⟨⟩ and Giorgos Keramidas ⟨⟩.


A few Hardware/OEM vendors tend to screw up BIOS settings, thus rendering the snd_hda driver useless, which usually results in a state where the snd_hda driver seems to attach and work, but without any sound. Some of that cases can be solved by tuning loader.conf variables. But before trying to fix problem that way, make sure that problem is really exists and the PCM audio device you are using really corresponds to expected audio connector.
Some vendors use non-standardized General Purpose I/O (GPIO) pins of codec to control external amplifiers. In some cases setting proper combination of GPIO bits may be needed to make sound work on specific device.
HDMI and DisplayPort audio may also require support from video driver.
January 22, 2010 Debian