* I have a timer function that monitors this
Please don’t do this.
Sent: Friday, October 30, 2020 6:31 AM
Subject: [EXTERNAL] [wdmaudiodev] Understanding
I was a bit confused by the function of the
IMiniportWaveRtInputStream::SetReadPacket methods, and the KEVENT passed into
If I understand it correctly, AllocateBufferWithNotification gets called with
notificationCount=2, and a buffer large enough for two 'packets'. Packets seem
to be sized to contain about 1/100 sec worth of audio frames.
RegisterNotificationEvent gets called with a single (in my case) event.
In the RENDER case, SetWritePacket(n, ...) is called when the OS has finished
copying packet <n> into whichever half of the buffer. I have a timer function
that monitors this, and transfers the packet to hardware (let's say). To let
the OS know that packet <n> has been processed (i.e., that packet in the buffer
is available), I call KeSetEvent(pNotificationEvent, 0, FALSE).
So this part isn't clear to me:
...kernel event that must be notified as DMA progresses. Depending on the
notification count parameter used with
the registered event is signaled __one or two times__ for every time that the
DMA passes through the audio buffer.
I expected there to be two calls to RegisterNotificationEvent, and thus two
KEVENT objects at any given time (one for each packet in the buffer). Instead,
I only see one getting added. The doc quote above seems to suggest that a
single event has to be set TWICE (or maybe set once, then the OS clears, then
set again)? I've looked at the KEVENT struct and related APIs, but I'm still
confused. Is this event supposed to signify "Buffer Complete" or "Packet
In the CAPTURE case, it looks like things are reversed. The OS calls
SetReadPacket to query the driver about which packet is available for reading
(transferring to client). RegisterNotificationEvent is getting called, so I
think the same (single) event is SET/CLEARED? by the OS to signal ME that it
has finished transferring data out of a packet, and that packet is available
for DMA again.
Thanks in advance for any and all help. :-)