[Openal] buffer size

[Peter Clare]

openal-bounces at opensource.creative.com wrote on 09/11/2006 11:07:33:
> It is not undocumented. It is documented under information about
> timers, "Win32 and COM development->System Services->SDK
> Documentation->Windows System Information->Time->About Time->Windows
> Time."

OK, documented but not well documented.  As you point out, the Windows Time
section says that the system timer runs at approx 10 ms (or 55 ms on Win
9x, 16 ms on Win NT 3.1).  But a relationship with the system timer isn't
mentioned in the documentation for the Win32 Sleep() function.  So someone
using Sleep() could easily be unaware of this.  Also, I've found no
documention that says that threads are scheduled using the Windows timer.
[The SDK section on thread scheduling talks mostly of priorities not time
intervals.]  It would be a reasonable guess that the Windows timer is used
for scheduling, but this is by no means a given (since there are higher
resolution timing mechanisms available).

Windows Vista has a new thing called MMCSS - MultiMedia Class Scheduler
Service - an improved scheduler designed specifically for multimedia apps.
A future Vista-specific version of the Generic Software OpenAL could make
good use of MMCSS.  And if it also used the new low-latency WASAPI API in
place of DirectSound for streaming the final output mix then that would
reduce the latency inside the OpenAL component.


> No kernel has a granularity of 1ms.

Agreed.  And certainly not a desktop O/S like Windows that was never
designed as an RTOS.


----
Peter Clare
Technical Director, Sensaura
Creative Labs
Meadlake Place, Thorpe Lea Road, Egham, Surrey, TW20 8HE, United Kingdom
Tel: +44 1784 476755
Email: pclare at sensaura.creative.com
Web: http://www.creative.com/ & http://www.sensaura.com/

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