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2013-07-13 16:46 <mth> larsc: on the JZ4770, if I power down the DAC, user space gets blocked when playing samples
2013-07-13 16:47 <mth> as in, the application is stuck in place until I enable one of the outputs that thereby indirectly enable the DAC
2013-07-13 16:47 <larsc> so the whole DMA is disabled?
2013-07-13 16:47 <mth> my guess is that the fifos don't get read anymore and therefore don't issue interrupts anymore either
2013-07-13 16:48 <larsc> If the codec is the clock master
2013-07-13 16:48 <larsc> and the clocks are disabled
2013-07-13 16:48 <larsc> as well
2013-07-13 16:48 <larsc> the i2s core won't request any new samples anymore
2013-07-13 16:48 <mth> I was wondering if this is a bug in the pcm or i2s driver or whether I simply shouldn't power down the DAC
2013-07-13 16:49 <mth> originally the codec driver didn't power down the DAC, but I've been cleaning it up and then this problem suddenly appeared
2013-07-13 16:49 <mth> the codec driver enables the clock at codec probe and never disables it
2013-07-13 16:49 <larsc> it probably shuts down more than just the DAC
2013-07-13 16:50 <mth> not ALSA, in any case: if I add a single line that only resets the DAC standby bit, the problem disappears
2013-07-13 16:50 <mth> maybe in the hardware there is also some kind of dependency graph?
2013-07-13 16:50 <mth> although the docs say they leave all that to software
2013-07-13 16:51 <larsc> yea, I'd assume that the codec shutsdown it's I2S clock if the DAC is powered down
2013-07-13 16:51 <larsc> or well the bit controls more than just the DAC
2013-07-13 16:52 <mth> so the I2S clock is sent by the codec to the AIC?
2013-07-13 16:53 <larsc> That's what I'd suspect
2013-07-13 16:54 <larsc> It's not unheard of that a codec tries to be smart and shutsdown the clocks if there is no active path over which audio could be played
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2013-07-13 16:57 <mth> the AIC is configurd to output SYSCLK, is that the same clock used for I2S or a different clock?
2013-07-13 16:57 <larsc> a different one, most likely
2013-07-13 16:57 <larsc> sysclk is usually the master clock
2013-07-13 16:57 <larsc> used by the codec to generate all other clocks
2013-07-13 16:58 <mth> "When use with the internal CODEC, the BIT_CLK and SYNC signals also with O_BIT_CLK and O_SYNC signals are provided by the internal CODEC from the SYSCLK, which is enabled by I2SCR.ESCLK and configured to 12MHz clock using CPM."
2013-07-13 16:58 <mth> so it seems there is a kind of loopback that derives the I2S clock from SYSCLK
2013-07-13 16:58 <mth> and perhaps powering down the DAC shuts down that loopback
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2013-07-13 17:01 <larsc> I wouldn't call it a loopback, but yes that's what is most likely happening
2013-07-13 17:03 <mth> yeah, it's more complex than just a wire, but the signal eventually gets sent back to the component where it came from
2013-07-13 17:04 <larsc> well it's comming from the cpm
2013-07-13 17:24 <mth> the AIC has a bit that controls whether it exports the SYSCLK or not
2013-07-13 17:24 <mth> so it's not coming directly from the CPM, but via the AIC
2013-07-13 17:25 <mth> anyway, do you have an idea on how to fix this?
2013-07-13 17:26 <mth> there doesn't seem to be a way to implicitly control the I2S clock
2013-07-13 17:26 <larsc> keep the DAC powered
2013-07-13 17:26 <mth> so one option would be to have the DAC enabled while playing with no outputs
2013-07-13 17:26 <mth> but it would waste some power
2013-07-13 17:26 <larsc> how often do you think somebody plays audio with all outputs disabled?
2013-07-13 17:27 <larsc> I mean it's not really a valid usecsae
2013-07-13 17:27 <mth> I do it quite often, if I'm playing games in the train
2013-07-13 17:27 <mth> I don't want to bother other people with the sound effects
2013-07-13 17:27 <mth> and often I'd rather disable sound than plug in headphones
2013-07-13 17:28 <larsc> But it would be better if the application would allow you disable sound altogether
2013-07-13 17:28 <mth> some do, but not every application has that option
2013-07-13 17:29 <larsc> Maybe you can somehow redirect audio to the null plugin
2013-07-13 17:29 <larsc> You do have a centeral deamon that handles stuff like volume right?
2013-07-13 17:29 <mth> I guess it's not trivial to have the samples consumed at the right rate if the dma is not running
2013-07-13 17:29 <mth> we have pwswd, which handles global hotkeys
2013-07-13 17:30 <mth> but it's not guaranteed that all volume changes go through that
2013-07-13 17:30 <larsc> but if you change the alsa config to use the null plugin is audio is off you'd save even more power
2013-07-13 17:31 <larsc> if audio is off
2013-07-13 17:32 <larsc> although I'm not sure how well that would work with already active streams
2013-07-13 17:33 <mth> maybe I'm over-optimizing and should just leave the DAC powered
2013-07-13 17:33 <larsc> leave it powered :)
2013-07-13 17:33 <mth> it took me several days to get the microphone support correct...
2013-07-13 17:33 <mth> although that was mostly because I'm not very good with ALSA yet
2013-07-13 17:33 <mth> and there is very little documentation on ALSA
2013-07-13 17:34 <mth> I am quite happy with how it turned out in the end though
2013-07-13 17:34 <mth> the platform data can now specify whether you have 0, 1 or 2 mono mics, or two mic inptus combined into one stereo mic
2013-07-13 17:35 <mth> and the right controls are instantiated for every case
2013-07-13 17:35 <mth> while previously you'd see all controls, even for inputs that don't exist on your board
2013-07-13 17:41 <larsc> sounds about right
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2013-07-13 18:52 <mth> larsc: this is what I came up with for the DAC power problem: http://www.treewalker.org/temp/force-sysclk.diff
2013-07-13 18:56 <larsc> have you checked whether there is a similar problem for capture?
2013-07-13 18:56 <mth> no, I haven't tested capture at all yet
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