I dumped appl_ptr and slave_appl_ptr being sent to mix_areas - and the numbers flow around the ring buffer in a steady circle. Here are graphs of the data:
http://www.caustik.com/alsa/scat-appl_ptr.gif http://www.caustik.com/alsa/scat-slave_appl_ptr.gif
So it looks like those values are moving like they should. However, I do not know where to print the hardware pointer value. Where is that variable?
Btw - I noticed that the kernel in core audio will manipulate some buffer pointers based on when the buffer is almost drained - is that relevant?
caustik
On 7/24/07, Takashi Iwai tiwai@suse.de wrote:
At Thu, 19 Jul 2007 12:59:32 -0700, Aaron "Caustik" Robinson wrote:
We have found that the problem exists because, at certain points in
time,
the hardware pointer and application pointer overlap. Basically the
hardware
is reading from the period buffer which is currently being written to.
How
might this be platform specific? Is there any debugging technique you
think
may help find the root cause?
It sounds unlikely a platform-specific problem but rather a problem of the driver implementation.
Note that the hw_ptr and appl_ptr tracked in pcm struct are within 0 and (runtime->boundary_size - 1). It's not within 0 and (buffer_size-1). So, basically it shouldn't overlap unless it goes across the boundary close to long (32bit or more).
Takashi
On 7/10/07, Jaroslav Kysela perex@suse.cz wrote:
On Tue, 10 Jul 2007, Aaron "Caustik" Robinson wrote:
This is on an embedded ARM device, with a custom driver. That's interesting. I never thought about the cache angle. Is there any
sort of
hack I can put to check if that is the problem?
The cache flush method is quite CPU specific, you have to check
datasheet.
But it's only guess and the problem might be somewhere else. I would compare samples DMA ring buffer in the user space and kernel space
again.
Also, put a debug lines to dmix plugin to detect where are samples
written
(to which pointer/area in the DMA ring buffer). dmix assumes that
playback
is running forever and tries to mix data in actual ring buffer
position.
Jaroslav
Jaroslav Kysela perex@suse.cz Linux Kernel Sound Maintainer ALSA Project, SUSE Labs
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