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1da177e4 LT |
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.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 | post-install sb /sbin/modprobe "-k" "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.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.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.conf 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. |