Hi,
Thanks for taking the time to answer about this detail.
On 20/03/12 13:10, Clemens Ladisch wrote:
Stefano Panella wrote:
I have been reading the documentation on "Writing an ALSA Driver" and I am still not completely clear on the meaning of the "pointer" callback in the pcm operations.
- In case of a playback stream, is the pointer referring to wich sample
is currently playing on the DAC or to which is it the last frame read by the HW from the alsa memory buffer?
It's the position of the first frame not yet read from the memory buffer.
The delay between the DMA and the DAC output would be reported by adjusting runtime->delay, but drivers usually do not bother to do this, except when this delay becomes rather large because of additional queueing, e.g., in the USB driver.
ok, I was wondering about applications like skype, trying to do some background noise cancellation, or to eliminate echo when using speakers. I was thinking in this case the delay should be accurate for Playback and Capture as well, or am I wrong?
- is there any test I could run to check I have implemented correctly
the "pointer" callback? Or any application which would need very high "pointer" precision like frame precision?
PulseAudio. Or run mplayer and look at the A-V value in the status line.
I will try these as well.
Regards, Clemens
In case this pv XEN alsa driver will start to work properly, where should I post the patches? Who is currently the linux kernel alsa driver mantainer?
Thanks again,
Stefano.