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/modprobe.d/oss.conf something like:
 30
 31alias char-major-14-* sb
 32install sb /sbin/modprobe -i sb && /sbin/modprobe 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
 39softdep sb post: 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
 63look at function referred to by module_init() for the card to see what
 64args are expected.
 65
 66 Note that at present there is no way to configure the io, irq and other
 67parameters for the modular drivers as one does for the wired drivers.. One
 68needs to pass the modules the necessary parameters as arguments, either
 69with /etc/modprobe.d/*.conf or with command-line args to modprobe, e.g.
 70
 71modprobe sb io=0x220 irq=7 dma=1 dma16=5 mpu_io=0x330
 72modprobe adlib_card io=0x388
 73
 74 recommend using /etc/modprobe.d/*.conf.
 75
 76Persistent DMA Buffers:
 77
 78The sound modules normally allocate DMA buffers during open() and
 79deallocate them during close(). Linux can often have problems allocating
 80DMA buffers for ISA cards on machines with more than 16MB RAM. This is
 81because ISA DMA buffers must exist below the 16MB boundary and it is quite
 82possible that we can't find a large enough free block in this region after
 83the machine has been running for any amount of time. The way to avoid this
 84problem is to allocate the DMA buffers during module load and deallocate
 85them when the module is unloaded. For this to be effective we need to load
 86the sound modules right after the kernel boots, either manually or by an
 87init script, and keep them around until we shut down. This is a little
 88wasteful of RAM, but it guarantees that sound always works.
 89
 90To make the sound driver use persistent DMA buffers we need to pass the
 91sound.o module a "dmabuf=1" command-line argument. This is normally done
 92in /etc/modprobe.d/*.conf files like so:
 93
 94options sound		dmabuf=1
 95
 96If you have 16MB or less RAM or a PCI sound card, this is wasteful and
 97unnecessary. It is possible that machine with 16MB or less RAM will find
 98this option useful, but if your machine is so memory-starved that it
 99cannot find a 64K block free, you will be wasting even more RAM by keeping
100the sound modules loaded and the DMA buffers allocated when they are not
101needed. The proper solution is to upgrade your RAM. But you do also have
102this improper solution as well. Use it wisely.
103
104  I'm afraid I know nothing about anything but my setup, being more of a
105text-mode guy anyway. If you have options for other cards or other helpful
106hints, send them to me, Jim Bray, jb@as220.org, http://as220.org/jb.