Hi,
El 10/07/14 17:39, Maxime Ripard escribió:
Lately, I have also been working on the audio part, now that I have
a working DMA driver. After implementing cyclic DMA transfers and
some clock code, and armed with a Buildroot image with mpg123 and an
OpenBSD release track[5] in mp3 format, I've been trying to get some
sound out of my Cubietruck's headphone jack, but without much
success so far. I have verified my userspace stack and hardware by
running these same binaries on top of the linux-sunxi 3.4 kernel,
and it worked fine. I have since then been dumping relevant
registers with devmem and comparing them, resolving issues as I see
them - hopefully this will yield some audible results.
What have you been working on? A new driver from scratch, tried to
take Allwinner's code and then cleant it up, or used the recently
published driver Jon made?
I've been working on top of Jon's codec patches. Seeing that the last
series Jon published on his github produces some sound, I got a fresh
copy of it today, and with some changes on DMAEngine, it's playing nicely.
As cyclic transactions are special (eg, they don't become empty) I
rewrote the cyclic support Jon had, making it issue subsequent transfers
directly from the interrupt request, and minimizing the number of times
this needs to be done. If we use the half done interrupt, we can get
away with one hardware programming per two periods.
It's rather late now and I still need to clean up the code a bit, but
I'll push a branch with these changes on my repo during the weekend.
Interestingly enough, Allwinner themselves do not seem to be using
cyclic DMA transfers on their driver[6]. I hope this is not a sign
of a hardware bug that's not documented.
So they just implement a cyclic-like behaviour in software?
Yep, they have this code to cycle through the buffer
https://github.com/linux-sunxi/linux-sunxi/blob/sunxi-3.4/sound/soc/sunxi/sunxi-codec.c#L648
Cheers!
Emilio
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