Linux Unleashed, Third Edition:Multimedia Linux





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Configuring a Sound Card
Some versions of Linux come with a routine that can link in support for your sound card. Usually you choose the type of sound card from a menu during the installation procedure, and the install routine takes care of the rest for you. If that’s the case, then the sound card should be properly working and you can skip this section. If your version of Linux didn’t ask about sound cards when it installed or your sound card is not working properly, you will have to go through the installation and configuration routine described here.


Note:  Some CD-ROMs of Linux software include sound card configuration routines that can’t be accessed until the operating system installation has been completed. Red Hat 5.0, for example, includes the utility sndconfig which can configure most SoundBlaster and compatible cards for you. Check your CD-ROM documentation to see which (if any) utilities have been provided for you.

The first step to setting up a sound card for Linux is to install the card itself. This is done by following the instructions that come with the sound card. There are no special steps that you must follow to configure a sound card for Linux, other than making sure the IRQ (interrupt), DMA (direct memory address), and I/O address are unique (which is necessary under DOS and Windows). If you installed the sound card already, you can obtain these settings from your Control Panel or other utilities. Some older sound cards use jumpers or DIP switches to establish these parameters. Whichever way they are set, you need to note them for your configuration under Linux.


Tip:  If you are using a sound card that supports Plug and Play, you should install it under Windows or DOS first because Linux doesn’t have the ability to set the parameters for these cards in most cases. After installing the card under Windows or DOS, use the Control Panel or similar utility to display the settings chosen for the sound card and note them. You’ll need to enter these values when setting up the card under Linux.If you are going to configure Linux sound cards, disable the PNP option in your system’s BIOS because it can cause configuration information on the Plug and Play cards to be reset to default values or to be changed entirely. Usually the BIOS has an option something like “PNP OS?” with the setting of Yes by default. Set this option to No for best results with Linux.


After installing the sound card, you need to link the proper sound card device driver into the kernel. If you haven’t worked with the kernel before, it’s not a scary process. You most likely didn’t have to link your kernel when you installed Linux, as most distributions come with prebuilt kernels which lack the sound card support. You need to recompile all the drivers (including the sound card driver) into a brand new kernel.
If you downloaded a device driver for your sound card from a Web or FTP site, chances are good that there is a README file of some sort with the driver itself. Make sure you read this file for any requirements the driver has (such as specific DMA or I/O addresses) and any special steps required during the recompilation of the kernel.
Every version of Linux has slightly different kernel recompile routines, but in general the steps are simple:

1.  Log in as root
2.  cd to /usr/src/linux
3.  Enter the command make config

Alternatively, some versions of Linux have an X-based utility to rebuild the kernel. For those systems, open a window and cd to the proper directory, then use the command make xconfig.
You must always be root when rebuilding the kernel; otherwise you won’t have access to the directories and utilities necessary to compile the kernel. Most versions of Linux keep the makefile for the recompile in /usr/src/linux, but if your version is different you should check the documentation or README files that came with your software.
When you run the config routine, it asks you a series of questions about whether you want to include certain components, as shown in Figure 21.1. In most cases, you will want to accept the defaults unless you know otherwise. One good example is when config asks whether you want to include a sound card (which is usually toward the end of a long list of questions). You should select yes. The config routine then asks a whole bunch of questions about which sound card to include, as shown in Figure 21.2.

Figure 21.1.  The config routine asks if you want to include components in your recompilation of the Linux kernel.

Figure 21.2.  The config routine asks a lot of questions about which sound card you want to support.
When you are asked for each type of sound card, answer N to the ones you know you are not using and Y to the one you want. Don’t let Linux guess your card, as it invariably guesses wrong.


Note:  If you had a sound card preconfigured in the kernel, config will ask you if you want to use it with a question like this:Old configuration exists in /etc/soundconf. Use it [Y/n]?
If you had a working sound card before, then answer Y. If your card did not work, then answer N.


After going through what may seem like a very long list of sound cards, you are asked some more generic questions that apply to many cards, such as


/dev/dsp and /dev/audio support [N/y]?


You should answer Y for this as the two devices mentioned are commonly used by sound card utilities. You are also asked if you want to use MIDI interface device support and FM synthesizer support:



MIDI interface support [N/y]
FM synthesis (YM2813/OPL-3) support [N/y]


If your card has a MIDI interface you should answer Y to the first. Many cards use a Yamaha FM synthesis chip to generate sound, in which case you should answer Y to the second (some cards support both MIDI and FM synthesis).

The last part of the sound card questions deal with the IRQ, DMA, and I/O address of the card. You should enter the values that you noted earlier for your sound card:


I/O base for SB
The default value is 220
Enter the value: 200

SoundBlaster IRQ
The default value is 7
Enter the value: 5

SoundBlaster DMA
The default value is 1
Enter the value: 1


You may be asked even more questions, depending on the sound card and the driver. Enter the values carefully since an error means you have to start the whole config process again.

To wrap up the sound card configuration routine, you’ll be asked whether you want to save the details:


The sound card has been configured.
Save copy of this configuration in /etc/soundconf [Y/n]






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