1Building a modular sound driver 2================================ 3 4 The following information is current as of linux-2.1.85. Check the other 5readme files, especially README.OSS, for information not specific to 6making sound modular. 7 8 First, configure your kernel. This is an idea of what you should be 9setting in the sound section: 10 11<M> Sound card support 12 13<M> 100% Sound Blaster compatibles (SB16/32/64, ESS, Jazz16) support 14 15 I have SoundBlaster. Select your card from the list. 16 17<M> Generic OPL2/OPL3 FM synthesizer support 18<M> FM synthesizer (YM3812/OPL-3) support 19 20 If you don't set these, you will probably find you can play .wav files 21but not .midi. As the help for them says, set them unless you know your 22card does not use one of these chips for FM support. 23 24 Once you are configured, make zlilo, modules, modules_install; reboot. 25Note that it is no longer necessary or possible to configure sound in the 26drivers/sound dir. Now one simply configures and makes one's kernel and 27modules in the usual way. 28 29 Then, add to your /etc/modules.conf something like: 30 31alias char-major-14 sb 32post-install sb /sbin/modprobe "-k" "adlib_card" 33options sb io=0x220 irq=7 dma=1 dma16=5 mpu_io=0x330 34options adlib_card io=0x388 # FM synthesizer 35 36 Alternatively, if you have compiled in kernel level ISAPnP support: 37 38alias char-major-14 sb 39post-install sb /sbin/modprobe "-k" "adlib_card" 40options adlib_card io=0x388 41 42 The effect of this is that the sound driver and all necessary bits and 43pieces autoload on demand, assuming you use kerneld (a sound choice) and 44autoclean when not in use. Also, options for the device drivers are 45set. They will not work without them. Change as appropriate for your card. 46If you are not yet using the very cool kerneld, you will have to "modprobe 47-k sb" yourself to get things going. Eventually things may be fixed so 48that this kludgery is not necessary; for the time being, it seems to work 49well. 50 51 Replace 'sb' with the driver for your card, and give it the right 52options. To find the filename of the driver, look in 53/lib/modules/<kernel-version>/misc. Mine looks like: 54 55adlib_card.o # This is the generic OPLx driver 56opl3.o # The OPL3 driver 57sb.o # <<The SoundBlaster driver. Yours may differ.>> 58sound.o # The sound driver 59uart401.o # Used by sb, maybe other cards 60 61 Whichever card you have, try feeding it the options that would be the 62default if you were making the driver wired, not as modules. You can look 63at the init_module() code for the card to see what args are expected. 64 65 Note that at present there is no way to configure the io, irq and other 66parameters for the modular drivers as one does for the wired drivers.. One 67needs to pass the modules the necessary parameters as arguments, either 68with /etc/modules.conf or with command-line args to modprobe, e.g. 69 70modprobe -k sb io=0x220 irq=7 dma=1 dma16=5 mpu_io=0x330 71modprobe -k adlib_card io=0x388 72 73 recommend using /etc/modules.conf. 74 75Persistent DMA Buffers: 76 77The sound modules normally allocate DMA buffers during open() and 78deallocate them during close(). Linux can often have problems allocating 79DMA buffers for ISA cards on machines with more than 16MB RAM. This is 80because ISA DMA buffers must exist below the 16MB boundary and it is quite 81possible that we can't find a large enough free block in this region after 82the machine has been running for any amount of time. The way to avoid this 83problem is to allocate the DMA buffers during module load and deallocate 84them when the module is unloaded. For this to be effective we need to load 85the sound modules right after the kernel boots, either manually or by an 86init script, and keep them around until we shut down. This is a little 87wasteful of RAM, but it guarantees that sound always works. 88 89To make the sound driver use persistent DMA buffers we need to pass the 90sound.o module a "dmabuf=1" command-line argument. This is normally done 91in /etc/modules.conf like so: 92 93options sound dmabuf=1 94 95If you have 16MB or less RAM or a PCI sound card, this is wasteful and 96unnecessary. It is possible that machine with 16MB or less RAM will find 97this option useful, but if your machine is so memory-starved that it 98cannot find a 64K block free, you will be wasting even more RAM by keeping 99the sound modules loaded and the DMA buffers allocated when they are not 100needed. The proper solution is to upgrade your RAM. But you do also have 101this improper solution as well. Use it wisely. 102 103 I'm afraid I know nothing about anything but my setup, being more of a 104text-mode guy anyway. If you have options for other cards or other helpful 105hints, send them to me, Jim Bray, jb@as220.org, http://as220.org/jb. 106