SOUND ON THE SEGA DREAMCAST

The Sega Dreamcast includes a ARM7 processor that seperately handles sound
playback. The ARM7 processor has its own address space which is only partially
accessible to the main SH4 processor.

The ALSA driver loads data to the ARM7 address space using DMA (which will
run at a good speed). The old OSS driver did not use DMA and so showed
very poor performance at high bit rates.

The driver also loads some simple firmware (seperately licenced under a 
modified BSD licence) which controls the ARM7 processor. Without the 
firmware the driver would merely fill the ARM7's address space and would 
not playback any sound.

The firmware, by default, should be loaded to /lib/firmware/ and should
be named aica_firmware.bin.