9 Aug
2015
9 Aug
'15
3:06 p.m.
Hi Andrew,
that's very nice to hear from you and we all are pretty much excited
here at the ReactOS Hackfest in Aachen that you are interested in audio
development again!
If you have a possibility - grab a ticket from London and come straight
away here, as the Hackfest lasts till 13th.
I hope Johannes could give you an overview of that area.
Regards,
Aleksey Bragin
On 09.08.2015 16:40, Andrew Greenwood wrote:
Hi everyone,
Some of you probably remember me. I was involved with trying to get
audio/sound implemented in ReactOS a few years ago.
To be honest, my progress was rather poor, I managed to write a few
bits of code but never really had a proper understanding of kernel/OS
development or CPU/system architectures. Additionally, whilst I could
grasp how the multimedia APIs (MME) in NT4 worked, and how they
interacted with the drivers (audio device X opens device Y and writes
buffered data to it) for Windows 2000 and later, Kernel Streaming was
used which partly built on top of the older implementation but added a
load of new stuff.
This complicated matters as firstly, KS uses COM (which I still
struggle to wrap my head around) in kernel-mode, secondly there were
multiple components involved between the application and the hardware
(wdmaud.drv -> wdmaud.sys -> ks.sys -> portcls.sys -> driver as far as
I remember), and finally I really struggled to find example code and
thorough documentation describing how it all worked.
Ultimately I gave up with that and intended to move to another
platform to develop multimedia applications. Not much happened with that.
I remember there were complaints from application developers over
Kernel Streaming offering poor latency – instead developers would turn
to other technologies such as ASIO or DirectSound. So for recent
versions of Windows (Vista onwards?) Microsoft implemented a new,
user-mode sound system (WASAPI) which again uses COM but is pretty
nicely documented, with code samples.
Having done a little reading about this, it renewed my interest. It
still uses COM, and KS.SYS is still present (I assume for
compatibility?) but as a lot of this is implemented in user-space I
suspect it’d be easier to develop/test.
Aside from this, over the past few years I’ve also gained a better
understanding of topics I didn’t know much about previously and I feel
more confident at being able to write lower-level stuff that works
properly. I’ve also developed more of a keen interest in how Windows
works.
So basically I’m considering implementing the current Windows audio
system in ReactOS. I’d imagine we don’t need to be too concerned about
audio drivers themselves (at least, initially) as vendors tend to
offer these and it’s not like we need sound immediately post-install!
The only thing I really lack now is knowledge of how to implement COM
classes – at least, outside of using Visual Studio… Anyone got
recommended reading or example code for this?
Andrew