7.2. 設定音效卡
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## 7.2. 設定音效卡

Contributed by Moses Moore.
加強 FreeBSD 5.X 的內容：Marc Fonvieille.

### 7.2.1. 設定系統

開始設定之前，必須先知道你的音效卡型號、晶片為何，以及是 PCI 或 ISA 規格。 FreeBSD 有支援許多種的 PCI、ISA 音效卡，請檢查支援的音效硬體表 Hardware Notes，以確認你的音效卡是否支援。 本文也會提到相對應該卡的驅動程式。

要使用音效卡，必須要載入正確的驅動程式才行。有兩種方式都可以完成這動作， 最簡單方式就是以 kldload(8) 來輕鬆載入 kernel 動態模組(module)， 像是下列指令：

`#` `kldload snd_emu10k1`

或者把相關驅動程式加到 `/boot/loader.conf` 檔，像是：

snd_emu10k1_load="YES"

上面例子是給 Creative SoundBlaster® Live! 音效卡使用的。 其他可用的音效卡驅動程式模組，可參考 `/boot/defaults/loader.conf` 範例。 若不確定到底該用哪一種驅動程式，那麼可以試試載入 `snd_driver` 模組看看：

`#` `kldload snd_driver`

This is a metadriver loading the most common device drivers at once. This speeds up the search for the correct driver. It is also possible to load all sound drivers via the `/boot/loader.conf` facility.

If you wish to find out the driver selected for your soundcard after loading the `snd_driver` metadriver, you may check the `/dev/sndstat` file with the `cat /dev/sndstat` command.

### 注意:

Under FreeBSD 4.X, to load all sound drivers, you have to load the `snd` module instead of `snd_driver`.

A second method is to statically compile in support for your sound card in your kernel. The section below provides the information you need to add support for your hardware in this manner. For more information about recompiling your kernel, please see 章 8, 設定 FreeBSD Kernel.

#### 7.2.1.1. Configuring a Custom Kernel with Sound Support

The first thing to do is adding the generic audio driver sound(4) to the kernel, for that you will need to add the following line to the kernel configuration file:

device sound

Under FreeBSD 4.X, you would use the following line:

device pcm

Then we have to add the support for our sound card. Therefore, we need to know which driver supports the card. Check the supported audio devices list of the Hardware Notes, to determine the correct driver for your sound card. For example, a Creative SoundBlaster® Live! sound card is supported by the snd_emu10k1(4) driver. To add the support for this card, use the following:

device snd_emu10k1

Be sure to read the manual page of the driver for the syntax to use. Information regarding the syntax of sound drivers in the kernel configuration can also be found in the `/usr/src/sys/conf/NOTES` file (`/usr/src/sys/i386/conf/LINT` for FreeBSD 4.X).

Non-PnP ISA cards may require you to provide the kernel with information on the sound card settings (IRQ, I/O port, etc). This is done via the `/boot/device.hints` file. At system boot, the loader(8) will read this file and pass the settings to the kernel. For example, an old Creative SoundBlaster® 16 ISA non-PnP card will use the snd_sbc(4) driver in conjunction with snd_sb16(4). For this card the following lines have to be added to the kernel configuration file:

device snd_sbc device snd_sb16

as well as the following in `/boot/device.hints`:

hint.sbc.0.at="isa" hint.sbc.0.port="0x220" hint.sbc.0.irq="5" hint.sbc.0.drq="1" hint.sbc.0.flags="0x15"

In this case, the card uses the `0x220` I/O port and the IRQ `5`.

The syntax used in the `/boot/device.hints` file is covered in the sound driver manual page. On FreeBSD 4.X, these settings are directly written in the kernel configuration file. In the case of our ISA card, we would only use this line:

device sbc0 at isa? port 0x220 irq 5 drq 1 flags 0x15

The settings shown above are the defaults. In some cases, you may need to change the IRQ or the other settings to match your card. See the snd_sbc(4) manual page for more information.

### 注意:

Under FreeBSD 4.X, some systems with built-in motherboard sound devices may require the following option in the kernel configuration:

options PNPBIOS

### 7.2.2. Testing the Sound Card

After rebooting with the modified kernel, or after loading the required module, the sound card should appear in your system message buffer (dmesg(8)) as something like:

pcm0: <Intel ICH3 (82801CA)> port 0xdc80-0xdcbf,0xd800-0xd8ff irq 5 at device 31.5 on pci0 pcm0: [GIANT-LOCKED] pcm0: <Cirrus Logic CS4205 AC97 Codec>

The status of the sound card may be checked via the `/dev/sndstat` file:

`#` `cat /dev/sndstat` FreeBSD Audio Driver (newpcm) Installed devices: pcm0: <Intel ICH3 (82801CA)> at io 0xd800, 0xdc80 irq 5 bufsz 16384 kld snd_ich (1p/2r/0v channels duplex default)

The output from your system may vary. If no `pcm` devices show up, go back and review what was done earlier. Go through your kernel configuration file again and make sure the correct device is chosen. Common problems are listed in 節 7.2.2.1, “Common Problems”.

If all goes well, you should now have a functioning sound card. If your CD-ROM or DVD-ROM drive is properly coupled to your sound card, you can put a CD in the drive and play it with cdcontrol(1):

`%` `cdcontrol -f /dev/acd0 play 1`

Various applications, such as `audio/workman` can provide a friendlier interface. You may want to install an application such as `audio/mpg123` to listen to MP3 audio files. A quick way to test the card is sending data to the `/dev/dsp`, like this:

`%` `cat `filename` > /dev/dsp`

where `filename` can be any file. This command line should produce some noise, confirming the sound card is actually working.

### 注意:

FreeBSD 4.X users need to create the sound card device nodes before being able to use it. If the card showed up in message buffer as `pcm0`, you will have to run the following as `root`:

`#` `cd /dev` `#` `sh MAKEDEV snd0`

If the card detection returned `pcm1`, follow the same steps as shown above, replacing `snd0` with `snd1`.

`MAKEDEV` will create a group of device nodes that will be used by the different sound related applications.

Sound card mixer levels can be changed via the mixer(8) command. More details can be found in the mixer(8) manual page.

#### 7.2.2.1. Common Problems

Error | Solution
--- | ---
unsupported subdevice XX | One or more of the device nodes was not created correctly. Repeat the steps above.
sb_dspwr(XX) timed out | The I/O port is not set correctly.
bad irq XX | The IRQ is set incorrectly. Make sure that the set IRQ and the sound IRQ are the same.
xxx: gus pcm not attached, out of memory | There is not enough available memory to use the device.
xxx: can't open /dev/dsp! | Check with `fstat | grep dsp` if another application is holding the device open. Noteworthy troublemakers are esound and KDE's sound support.

### 7.2.3. Utilizing Multiple Sound Sources

Contributed by Munish Chopra.

It is often desirable to have multiple sources of sound that are able to play simultaneously, such as when esound or artsd do not support sharing of the sound device with a certain application.

FreeBSD lets you do this through Virtual Sound Channels, which can be set with the sysctl(8) facility. Virtual channels allow you to multiplex your sound card's playback channels by mixing sound in the kernel.

To set the number of virtual channels, there are two sysctl knobs which, if you are the `root` user, can be set like this:

`#` `sysctl hw.snd.pcm0.vchans=4` `#` `sysctl hw.snd.maxautovchans=4`

The above example allocates four virtual channels, which is a practical number for everyday use. `hw.snd.pcm0.vchans` is the number of virtual channels `pcm0` has, and is configurable once a device has been attached. `hw.snd.maxautovchans` is the number of virtual channels a new audio device is given when it is attached using kldload(8). Since the `pcm` module can be loaded independently of the hardware drivers, `hw.snd.maxautovchans` can store how many virtual channels any devices which are attached later will be given.

### 注意:

You cannot change the number of virtual channels for a device while it is in use. First close any programs using the device, such as music players or sound daemons.

If you are not using devfs(5), you will have to point your applications at `/dev/dsp0`.`x`, where `x` is 0 to 3 if `hw.snd.pcm.0.vchans` is set to 4 as in the above example. On a system using devfs(5), the above will automatically be allocated transparently to the user.

### 7.2.4. 設定預設(Mixer Channel)的音量大小

Contributed by Josef El-Rayes.

### 注意:

本功能只有在 FreeBSD 5.3-RELEASE 及之後版本才有支援。

The default values for the different mixer channels are hardcoded in the sourcecode of the pcm(4) driver. There are a lot of different applications and daemons that allow you to set values for the mixer they remember and set each time they are started, but this is not a clean solution, we want to have default values at the driver level. This is accomplished by defining the appropriate values in `/boot/device.hints`. E.g.:

hint.pcm.0.vol="100"

This will set the volume channel to a default value of 100, when the pcm(4) module is loaded.

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