[linux-audio-dev] Re: How does ASIO work?

I am preparing some slides about Linux audio, and while comparing Linux with Windows, I have been wondering how the ASIO drivers manage to obtain low latency on MS Windows, an operating system that does not seem capable of low latency in any other way. So what tricks did Steinberg come up with to get around that? I'd like to be able to say why the Linux approach is better/cleaner. <<< ASIO provides an interface directly to the kernel mode driver, typically through a private device I/O control between the user mode ASIO DLL and the kernel mode driver. By talking right to the driver, they bypass the system component known as KMIXER, which adds 30 msec of latency to all audio in Windows. But ASIO isn't the only way around KMIXER. With the advent of Win32 Driver Model (WDM) Kernel Streaming (KS), the Windows O/S is indeed capable of very low latency. WDM KS has a standardized device I/O control set that's part of the Windows audio stack. KS makes it possible to stream audio at sub 5-msec latency -- approaching 1 msec latency -- using a direct interface to the "miniport" driver in the Windows driver stack. I wrote a white paper about all this a few years back: http://www.cakewalk.com/DevXchange/audio_i.asp There's a diagram of the audio stack in Windows which might be helpful. Note that we never needed to create custom IOCTLs for Windows. Microsoft followed up after this meeting by disclosing the Windows kernel IO controls for everyone to use, known as DirectKS: http://www.microsoft.com/whdc/device/audio/DirectKS.mspx As far as I know the ASIO4All driver is built using DirectKS. ---------- Ron Kuper VP / Engineering Cakewalk http://www.cakewalk.com