ASC/EASC audio device

Greetings,

Please see the diff at: ftp://ftp.netbsd.org/pub/NetBSD/misc/nat/asc-audio.diff

it sould be applied via patch within the sys/arch directory.

It allows the Enhanced Apple Sound Chip (easc) to be used as an audio device.

The asc0 bell driver would not attach to the easc as it does not support wave 
table mode.

With this driver a wsbell is provided for WSFB* kernels

Currently recording does not work.

This should also work for the asc as well but I don't have the hardware to 
test so community feedback would be helpful.

There are currently to compile time options (for which one will be chosen 
pending your feedback) in ascaud.c USE_INTRS.

If USE_INTRS is set to 1 the default is to use interrupts to keep the devices 
sound buffers full.

If USE_INTRS is set to 0 the sound buffers are kept full via scheduling a 
callout.

Please let me know (I'm not subscrbed to the list) if this works on machines 
with the asc as well and what setting of USE_INTRS yields the best result.

Best regards,

Nat