On 1/6/17 10:08 AM, Ricardo Biehl wrote:
2017-01-06 6:09 GMT-02:00, Clemens Ladisch <clemens@xxxxxxxxxx>:
Are you talking about code in your driver (where you are responsible for
asking the hardware), or user space code (where you must not directly
read hw_ptr)? What is the actual problem you're trying to solve?
Hello!
I'm developing a "live microphone system over local network" which are user
space programs (clients => server) transferring audio nearly real-time
(human imperceptible latency).
I need to elaborate a good solution of implementation to have everything working
as expected -- networking, scheduling, IO management etc -- However I need at
first make sure I can get control over audio.
I decided to use ioctl() level of communication with ALSA in kernel, and what I
need is synchronization :-)
I must know which sample the hardware is currently processing to prevent a lot
of losses or latency increasing.
I would hate to sound pedantic but sample-accurate control (10us at
48kHz) is far from trivial. The hw_ptr points to the ring buffer, but
you may have additional samples queued up in DMA transfers, FIFOS,
codecs and last some analog delays. On a network-based solution the
different components typically don't use the same audio clock and you
will have to deal with drifts between source and sink.
Best of luck.
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