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Based on kernel version 3.16. Page generated on 2014-08-06 21:41 EST.

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