Jeff,
Each port pin in WavePci has an instance of an IrpStream object
associated with it. The IrpStream object facilitates all of the streaming
IRP helper functionality for the pin, including queue management, mapping
and unmapping. The IrpStream object contains an internal member variable
that keeps track of the starvation state of the pin. For discussion
purposes, call this variable WasExhausted. This variable is initialized
to TRUE when the object is created (pin/stream create time). As IRPs
arrive the IrpStream object performs some management tasks (creates and
initializes a mapping context and sticks the IRP into a cancellable
mapping queue) and then looks at the WasExhausted variable. If the value
of WasExhausted is TRUE, it sets the value of WasExhausted to FALSE and
calls IrpSubmitted on the port pin, which in turn calls MappingAvailable
on the miniport stream.
When GetMapping is called it attempts to get the next previously
mapped mapping. If there are no previously mapped mappings available it
grabs the next available IRP off of the mapping queue. If there is an IRP
available it attempts to map the IRP to obtain a mapping. The bottom line
here is that if a mapping cannot be obtained when you call GetMapping the
variable WasExhausted is set to TRUE (and MappingAvailable is called when
the next IRP arrives). It should be fine to call GetMapping without
waiting for a MappingAvailable call.
Note that in the description above there is no mention of pin/stream
state dependencies. MappingAvailable is called in response to IRP
arrival, not state transitions. Unfortunately I don't have easy access to
more than a couple years of change history for the portcls code and,
frankly, I simply don't remember every detail from the Win98/Win2K days so
I can't give you a reliable answer about the behavior differences between
Win2K and XP/Vista.
Ken
-----Original Message-----
From: wdmaudiodev-bounce@xxxxxxxxxxxxx
[mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Jeff Pages
Sent: Tuesday, March 27, 2007 4:15 PM
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] Re: WavePCI issue with multiple processors
Hi Ken,
Thanks for that information. Is there anything more you can tell me about
calls to MappingAvailable? The current documentation says it should only
be
called when a previous call to GetMapping has failed. The call when the
stream is new doesn't happen in Windows 2000, only in XP and later it
seems.
It looks like it happens when the stream state changes from KSSTATE_PAUSE
to
KSSTATE_ACQUIRE - is this correct?
Also, is it really safe in a multiprocessor environment to keep calling
GetMapping after it has failed, or should I wait until I get a call to
MappingAvailable?
Jeff
----- Original Message -----
From: "Ken Cooper" <Ken.Cooper@xxxxxxxxxxxxx>
To: <wdmaudiodev@xxxxxxxxxxxxx>
Sent: Tuesday, March 27, 2007 3:14 PM
Subject: [wdmaudiodev] Re: WavePCI issue with multiple processors
MappingAvailable is called in two circumstances. The first case is when
a
new streaming irp arrives. After the IRP is added to the mapping queue
MappingAvailable is called if the driver is currently starved (the stream
is new or the previous call to GetMapping failed). The second case is in
response to setting the pin position via position property.
The lock issue across GetMapping and ReleaseMapping has been complicated
since the WavePci port was written back in the Win98 days.
Unfortunately,
if you attempt to hold a spinlock for your mapping list when you call
these routines you'll likely deadlock with the spinlock that portcls uses
to protect access to it's mapping and unmapping queues.
I don't have the code in front of me at the moment but I'll take a closer
look tomorrow at the portcls and WDK sample code and respond with a
little
more detail.
Incidentally, portcls doesn't care at all about your tag values other
than
that the outstanding tags at any given moment be unique. They can be
monotonically increasing if you like, or they could be addresses into
list
of mappings. It's up to you.
Ken
________________________________________
From: wdmaudiodev-bounce@xxxxxxxxxxxxx [wdmaudiodev-bounce@xxxxxxxxxxxxx]
On Behalf Of Jeff Pages [jeff@xxxxxxxxxxxxxxxx]
Sent: Monday, March 26, 2007 6:58 PM
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] Re: WavePCI issue with multiple processors
Hi Eugene,
A probability of that a new mapping becomes available exactly within
this window, is almost zero.
You're right, of course. I was thinking I had to reacquire my spin lock
after the unsuccessful call to GetMapping, but looking at it now, that's
not
necessary, and I can just call InterlockedDecrement on my
InAcquisitionLoop
variable and exit.
And a well-optimized driver itself cannot guarantee that all Windows
audio subsystems will function quickly and reliably. Even DirectSound
with hardware buffers introduces a significant overhead and software
buffers and/or MME introduce much more overhead. So you can achieve a
reproducible high performance only if your well-optimized application
uses your well-optimized audio driver directly via its wave/topology
interfaces.
For this particular application, I'm using the Vista Core Audio API in
exclusive mode, and this was when some of the wrinkles in my WavePCI
drivers
started showing up. I'm now using your suggestion with the interlocked
InAcquisitionLoop variable and so far it's all hanging in there!
Thanks for your help.
Jeff
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