[wdmaudiodev] Re: Multi-channel audio USB driver development
- From: "Daire O'Neill" <oneill.daire@xxxxxxxxx>
- To: wdmaudiodev@xxxxxxxxxxxxx
- Date: Wed, 7 Jul 2010 23:45:55 +0900
Tim, Robert, and Jerry
Many thanks for your replies, and sorry for my slow response. I will
do some more research and see if I can get away
with not having to write a driver, otherwise I may be back with some
more questions.
Regards,
Daire
On Fri, Jul 2, 2010 at 2:56 AM, Jerry Evans <jerry@xxxxxxxxxxx> wrote:
> Hello Daire
>
> I think you've got a classic need for compromise here :)
>
> Assuming your USB device is playback only ....
>
> Streaming using KS from user mode on XP will give you ~10ms latency (best
> case) with the XP driver. However I don't think you'll get anything more
> than stereo working. Not sure the XP class driver groks multi-channel
> hardware. Certainly did not work back in '05 with custom 6 channel board
> here. H/W worked with OSX ...
>
> USB performance is, I believe, much better on W7. Recent postings in this
> group indicated you can reduce USB bus latency to 4ms. Favourite would have
> to be KS as well for compatibility.
>
> As Tim has pointed out, ASIO4ALL provides an industry standard (and simpler)
> API for any Windows compatible hardware. Performance is good and Michael may
> still be amenable to bundling if modestly rewarded. Not sure if XP
> multi-channel limitations apply as faults we encountered may have been
> problems with my KS interface.
>
> All of that said, there are a couple of other options. If your hardware uses
> Cypress parts (for example) you can use their own driver with which you
> could implement your own device communication. On XP and W2K (why?) you
> might get better performance than the in-box driver, esp. with multi-channel
> audio, but probably not on W7. There are also 3rd party USB drivers from
> outfits like this: http://www.thesycon.de/eng
>
> I'd strongly recommend *not* writing anything from scratch unless you want
> to turn the project into a career.
>
> Clearly YMMV considerably. It's unclear whether your project is
> research/commercial/consumer? with your own hardware or third party? level
> of price sensitivity? All will clearly impact the decision making process.
>
> Finally 20 ms is *not* low latency. It is easily heard when monitoring a
> recording or playing software instruments.
>
> HTH
>
> Jerry
>
> On 01/07/2010 13:42, Daire O'Neill wrote:
>
> Hi Tim, many thanks for your reply.
>
>
>
>
> ASIO also operates like this for low-latency, does this mean that ASIO
> is essentially an audio driver that follows the WDM-KS format?
>
>
> Well, not really. ASIO is mostly a user-mode framework. It allows
> applications to bypass the intermediate layers and talk directly to the
> manufacturer's audio driver, much like DirectKS. An ASIO "driver" is a
> (thin) user-mode wrapper around an existing kernel-mode driver. It
> would be possible, I suppose, to create a separate kernel-mode driver
> that pairs directly with an ASIO driver, but to my knowledge no one does
> that.
>
>
>
> DirectKS is an API that can be used to write kernel streaming drivers,
> with similarly low latency to ASIO.
>
>
> No. DirectKS is a user-mode API that allows applications to access
> kernel streaming drivers. It is not used to WRITE kernel streaming drivers.
>
>
> So, I need to write a "wrapper" around the existing kernel-mode driver
> (eg usbaudio.sys), possibly
> using the DirectKS API? How does DirectKS relate to the AVStream class?
>
> The DDK docs mention that WDMAud.sys performs I/O for the WaveIn / Out
> APIs, so I can use
> those APIs to send audio directly to the driver kernel?
>
>
>
>
> Nothing. If your device meets USB Audio Class, you don't write
> anything. Microsoft provides usbaudio.sys, and ASIO4ALL provides the
> ASIO layer for ASIO applications.
>
>
> However, doesn't this assume that the end user will have ASIO4ALL installed?
> What if I want my hardware to operate independently of ASIO4ALL, then
> I need to write a
> "wrapper" driver similar to ASIO4ALL, as mentioned above?
>
>
>
>
> USB audio device manufacturers don't write drivers.
>
>
> Really? Even in the absence of an ASIO4ALL driver on the users PC?
> What about for pro-audio products, which is what I am developing for?
> For example this company provides their own USB drivers:
> http://www.esi-audio.com/
>
> I have read the same as what you are saying from the DDK docs:
> "When an audio device identifies itself as USB Audio-compliant
> during Plug and Play device enumeration,
> the system automatically loads the USBAudio driver to drive the
> device. USBAudio drives the device directly,
> without the aid of a proprietary adapter driver. This means that a
> device that complies with the USB audio specifications
> requires no proprietary adapter driver."
>
> But, if thats the case, why do companies such as above provide
> drivers? This confuses me, so if you could explain it would be great.
>
>
>
>
> Up to this point, you have not defined what "low latency" means to you.
>
>
> I'm estimating about 20ms.
>
> Could you recommend the most sensible way to approach writing for multiple
> OS,
> namely Win2K, XP, Vista, 7? I would like to re-use as much code as possible.
> Do you think 6 months is a reasonable estimate for development time?
>
> Many thanks, its really appreciated.
>
> Daire
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