[wdmaudiodev] Re: USB2.0 High speed audio device for windows XP
- From: Tim Roberts <timr@xxxxxxxxx>
- To: wdmaudiodev@xxxxxxxxxxxxx
- Date: Wed, 20 Feb 2008 10:39:43 -0800
carsten_30_@xxxxxx wrote:
if you remember my first question, it was: "How can i make avssamp
appear as a system audio device, because I want to develop a kernel
streaming driver (based on avssamp) wich deals with my USB2.0 audio
device. But all trys to access this WDM KS driver as a system audio
device fail. Waht must I do? Change topology, AddInterfaces in the
inf, what is the way?" Your answer was(and sounds like an accusation):
"May I ask why you are not using usbaudio.sys? I cannot imagine
anyone in the last 5 years who would have designed a USB-based audio
device that was not USB Audio Class compliant."
That was not an accusation. When I asked that question, I did not
realize that usbaudio.sys contained a senseless, arbitrary, and
unjustified limitation on the bandwidth of the isochronous pipes. There
is nothing in the USB Audio Class 1.0 spec that calls for such a
limitation, and it is astonishing to me that Microsoft would have
embedded it in the driver.
I have since learned that this limitation exists, which is why I have
now backed out of the conversation.
What should I say? You can not imagine anyone in the last 5 years, who
needs USB2.0 bandwidth with audio!!!
No, that's not the issue. I can certainly imagine your bandwidth
requirements. What I could not imagine was that the Microsoft
developers would intentionally limit a general-purpose driver like
usbaudio.sys without justification.
And for me is usbaudio.sys useless!!!
Yes, now I see this.
But, by the way, I have learned a lot about MS-Audio in the the last
two weeks. But the more I know the more and more confusing became
usbaudio.sys. here are some examples:
If I report more than one sample rate in the Class Specific Audio
Streaming Interface Descriptor,like this
;; class specific Audio Streaming interface Descriptor
db 7 ;; length
db CS_INTERFACE ;; Type
db GENERAL ;; Sub type
db 2 ;; bTerminalLink (ID of Output Terminal)
db 1 ;; bDelay
dwi 1 ;; wFormat (PCM=0001)
;; FormatDescriptor
db 0BH ;; length
db CS_INTERFACE ;; Descriptor type
db FORMAT_TYPE ;; Sub Type (Format_Type)
db FORMAT_TYPE_I ;;
db NumChannels ;; # channels
db 2 ;; byte per subframe
db 16 ;; Bits per Sample
db 2 ;; #frequncies supportred
db 0x80,0xBB,0x00 ;; 48 khz
db 0xF0, 0x55, 0x00 ;; 22 Khz
the device doesn't appear as a system audio device no more.
Do you remember the USB camera descriptor set I posted earlier in the
week? It does this (in fact, it offers 7 options), and it appears as a
system audio device. It includes the frequencies in increasing
numerical order, but I don't think that is required by the spec.
The length in your descriptor is incorrect. The descriptor is 14 bytes
long, but you have the length as 11. That will cause usbaudio.sys to
reject you.
How will usbaudio.sys select one of the repoerted sample rates (i
havn't found a request for this).
Ah, now THAT one I can answer, because I've just been monitoring an
exchange that does this.
The sampling frequency request is in 5.2.3.2.3.1 of the Audio Class
spec. It's a class-specific endpoint request, with bRequest=SET_CUR,
wValue=SAMPLING_FREQ_CONTROL<<8 (which is 0x0100), wIndex set to the
streaming endpoint number, and a 3-byte data value containing the
sampling rate in Hz.
Oddly, we have one camera were this does get sent, and one where it does
not. I'm not yet sure why.
--
Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.
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