Newbie - USB Audio Driver Questions
Newbie - USB Audio Driver Questions
- Subject: Newbie - USB Audio Driver Questions
- From: Ron Wilson <email@hidden>
- Date: Wed, 18 Jun 2003 10:58:45 -0700
Hi All,
I'm an experienced Mac Developer, but a complete newbie to CoreAudio.
I've taken on the task of developing USB Audio and MIDI drivers for a 2
channel device that provides analog and digital input/output, and some
hardware processing (compressor, parametric equalizer, etc.).
I've been reading all I can find of Apple's audio developer
documentation and I've got a few questions. Any help/advice is greatly
appreciated.
In "Writing Audio Device Drivers", page 17 "Apple Audio Drivers", I
found this: "These drivers are suitable for much of the audio hardware
commonly found on Power PC computers. The "onboard driver" kernel
extension AppleOnboardAudio.kext contains almost a half dozen audio
drivers packaged as plug-ins" ... "For USB audio hardware, Apple
includes the driver defined in the AppleUSBAudio.kext kernel extension."
On the Apple web site, at
"
http://developer.apple.com/audio/coreaudio.html";, I find this:
"Although it is possible to create custom plug-ins for the Audio HAL
that allow you to fully access your hardware, you actually shouldn't
need to do this. Apple provides you with a set of drivers for
different transport layers: these are for built-in hardware of course,
but also included is a USB class driver compliant with the USB audio
specification ."
OK, so my questions:
1) Looking at the USB audio specification "USB Device Class Definition
for Audio Devices", it seems to me that our device will have
capabilities and requirements (controlling the parametric equalizer
parameters at the least) that are beyond what is covered in this spec.
Am I reading that correctly?
2) I'm concerned about additional overhead and/or latency that would
result if I did not provide a device specific driver. Does anyone know
whether the Apple supplied drivers will provide for tweaking buffer
sizes, timing, latency etc.?
At this point I'm pretty much convinced that I'll be writing a device
specific driver.
Thanks,
--Ron
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