Running Linux, 5th Edition - Matthias Kalle Dalheimer [162]
Configuring the kernel (optional)
In the most common situation, where you are running a kernel that was provided during installation of your Linux system, all sound drivers should be included as loadable modules and it should not be neccessary to build a new kernel.
You may want to compile a new kernel if the kernel sound driver modules you need are not provided by the kernel you are currently running. If you prefer to compile the drivers directly into the kernel rather than use loadable kernel modules , a new kernel will be required as well.
See Chapter 18 for detailed information on rebuilding your kernel.
Configuring kernel modules
In most cases the kernel sound drivers are loadable modules, which the kernel can dynamically load and unload. You need to ensure that the correct drivers are loaded. You do this using a configuration file, such as /etc/conf.modules. A typical entry for a sound card might look like this:
alias sound sb
alias midi opl3
options opl3 io=0x388
options sb io=0x220 irq=5 dma=1 dma16=5 mpu_io=0x330
You need to enter the sound driver to use and the appropriate values for I/O address, IRQ, and DMA channels that you recorded earlier. The latter settings are needed only for ISA and ISA PnP cards because PCI cards can detect them automatically. In the preceding example, which is for a 16-bit Sound Blaster card, we had to specify the driver as sb in the first line, and specify the options for the driver in the last line.
Some systems use /etc/modules.conf and/or multiple files under the /etc/modutils directory, so you should consult the documentation for your Linux distribution for the details on configuring modules. On Debian systems, you can use the modconf utility for this task.
In practice, usually the only tricky part is determining which driver to use. The output of pnpdump for ISA PnP cards and lspci for PCI cards can help you identify the type of card you have. You can then compare this to documentation available either in the Sound HOWTO or in the kernel source, usually found on Linux systems in the /usr/src/linux/Documentation/sound directory.
For example, a certain laptop system reports this sound hardware in the output of lspci:
00:05.0 Multimedia audio controller: Cirrus Logic CS 4614/22/24 [CrystalClear
SoundFusion Audio Accelerator] (rev 01)
For this system the appropriate sound driver is cs46xx. Some experimentation may be required, and it is safe to try loading various kernel modules and see if they detect the sound card.
Testing the installation
The first step to verify the installation is to confirm that the kernel module is loaded. You can use the command lsmod; it should show that the appropriate module, among others, is loaded:
$ /sbin/lsmod
Module Size Used by
parport_pc 21256 1 (autoclean)
lp 6080 0 (autoclean)
parport 24512 1 (autoclean) [parport_pc lp]
3c574_cs 8324 1
serial 43520 0 (autoclean)
cs46xx 54472 4
soundcore 3492 3 [cs46xx]
ac97_codec 9568 0 [cs46xx]
rtc 5528 0 (autoclean)
Here the drivers of interest are cs46xx, soundcore, and ac97_codec. When the driver detected the card, the kernel should have also logged a message that you can retrieve with the dmesg command. The output is likely to be long, so you can pipe it to a pager command, such as less:
PCI: Found IRQ 11 for device 00:05.0
PCI: Sharing IRQ 11 with 00:02.0
PCI: Sharing IRQ 11 with 01:00.0
Crystal 4280/46xx + AC97 Audio, version 1.28.32, 19:55:54 Dec 29 2001
cs46xx: Card found at 0xf4100000 and 0xf4000000, IRQ 11
cs46xx: Thinkpad 600X/A20/T20 (1014:0153) at 0xf4100000/0xf4000000, IRQ 11
ac97_codec: AC97 Audio codec, id: 0x4352:0x5914 (Cirrus Logic CS4297A rev B)
For ISA cards, the device file /dev/sndstat shows information about the card. This won't work for PCI cards, however. Typical output should look something like this:
$ cat /dev/sndstat
OSS/Free:3.8s2++-971130
Load type: Driver loaded as a module