It's hard to do the low-level hardware stuff outside the kernel. It's possible, but it's a lot easier inside. Just keep the inside simple.
I've done audio on a handful of operating systems and all I ever want to do with the card is set it up to play X kHz 16-bit little-endian PCM stereo and then control the volume. The rest can be done from user space. This is exactly what Plan 9's audio driver already does, and I wish the others were so simple. The original post commented that only supporting PCM was too simplistic, but I argue it's exactly right. PCM is the native hardware sample format and is basically the "uncompress bitmap" of the audio world. Defining a fixed byte order avoids one level of misconfiguration and complexity; it doesn't matter which is chosen except that the existing driver is little endian. Being able to change the sample rate is necessary for quality; it is too hard to resample other speeds nicely on the fly, and the hardware will take care of it for you. The fixed 16-bit and stereo parts are perhaps debatable, but basically no one has 8-bit audio they care about, it is trival to convert 8-bit to 16-bit, and it is also trivial to turn mono into stereo. If you want a different device file into which you can write mp3 and other sound file formats, great: do it in user space, translating into the native hardware format. By analogy, Plan 9's kernel gives user space access to the raw disk bytes. It doesn't implement the interpretation of those bytes as 9660, fat, ext2, kfs, venti, or other disk "file formats". That can be done better and more easily in user space. The same is true of audio. There's already a good native hardware format and a well-established and capable (if simple) kernel interface. Leave those alone and put the extra complexity in user space for those who want to use it. Russ P.S. My guess is that Inferno's implementation of mp3 in the kernel device file was a quick way to make an mp3 decoder available without writing one in Limbo. It may have had something to do with making a snazzy low-bandwidth import-across-the-network demo too. But neither of those applies to Plan 9, since the same can be accomplished with a C program running in user space.
