[alsa-devel] Channel swapping problem on Atmel SSC audio
Hi all,
I'm working on a custom board using the AT91SAM9G45 processor and a TLV320AIC26 SPI attached audio codec using I2S format audio. When doing audio playback on the board the left and right channels are occasionally flipped.
I have verified this by generating a custom wav file which has constant data on one channel and an incrementing counter on the other channel. The digitial out from the CPU shows that no data is being lost, but around 1/5 times the audio channels will be flipped. The problem appears to be that the DMA is starting on the wrong edge of the LRCLK.
I have using both SND_SOC_DAIFMT_CBM_CFM (Codec provides clocks) and SND_SOC_DAIFMT_CBS_CFS (CPU provides clocks) but the problem occurs in both situations. I have also tried changing TCMR:CKO to SSC_CKO_TRANSFER and TCMR:START to SSC_START_LOW_RF, but the problem still occurs. I have looked through the PCM/SSC DMA code and cannot find any obvious bugs.
I have checked the errata for the At91SAM9G45 processor (our chip marking is CU-1004-A), but can't find anything which relates directly to the problem we are seeing.
Has anybody else had this problem, or does anybody have any AT91/Atmel hardware that they could test to see if it occurs on other hardware also?
Thanks, ~Ryan
On Wednesday 10 November 2010 22:49, Ryan Mallon wrote:
I'm working on a custom board using the AT91SAM9G45 processor and a TLV320AIC26 SPI attached audio codec using I2S format audio. When doing audio playback on the board the left and right channels are occasionally flipped.
<snip>
Has anybody else had this problem, or does anybody have any AT91/Atmel hardware that they could test to see if it occurs on other hardware also?
I have worked with the AT91SAM9260 on a project which is currently suspended (other priorities), where we had a simiar problem, with a codec on SPI. Every time audio was started (capture or playback) the channels could be swapped. Solving that issue remains TODO when we restart.
There was a thread on alsa-devel last month 'Soc Atmel SSC stereo problem' with some suggestions.
HTH,
Alan
Am 11.11.2010 13:27, schrieb Alan Horstmann:
On Wednesday 10 November 2010 22:49, Ryan Mallon wrote:
I'm working on a custom board using the AT91SAM9G45 processor and a TLV320AIC26 SPI attached audio codec using I2S format audio. When doing audio playback on the board the left and right channels are occasionally flipped.
<snip>
Has anybody else had this problem, or does anybody have any AT91/Atmel hardware that they could test to see if it occurs on other hardware also?
I have worked with the AT91SAM9260 on a project which is currently suspended (other priorities), where we had a simiar problem, with a codec on SPI. Every time audio was started (capture or playback) the channels could be swapped. Solving that issue remains TODO when we restart.
There was a thread on alsa-devel last month 'Soc Atmel SSC stereo problem' with some suggestions.
In the thread mentioned, Alan proposed me amongst other things to test the LRCK level before starting the SSC. This works well for me. Maybe it should be implemented in a more generic way but the following modification does the trick for me.
in function atmel_pcm_trigger inside file sound/soc/atmel/atmel-pcm.c :
case SNDRV_PCM_TRIGGER_START: +while(!at91_get_gpio_value(AT91_PIN_PB12)); +while(at91_get_gpio_value(AT91_PIN_PB12));
case SNDRV_PCM_TRIGGER_RESUME: +while(!at91_get_gpio_value(AT91_PIN_PB12)); +while(at91_get_gpio_value(AT91_PIN_PB12));
Patrick
I had faced the similar issue on IMx31. The cause there was reversal of LRCK clock {180 degree phase shift}. probing the LRCK clock may help you to find the problem
________________________________________ From: alsa-devel-bounces@alsa-project.org [alsa-devel-bounces@alsa-project.org] On Behalf Of Patrick Ziegler [patrick.ziegler@fh-kl.de] Sent: Friday, November 12, 2010 1:36 PM To: alsa-devel@alsa-project.org Cc: Ryan Mallon Subject: Re: [alsa-devel] Channel swapping problem on Atmel SSC audio
Am 11.11.2010 13:27, schrieb Alan Horstmann:
On Wednesday 10 November 2010 22:49, Ryan Mallon wrote:
I'm working on a custom board using the AT91SAM9G45 processor and a TLV320AIC26 SPI attached audio codec using I2S format audio. When doing audio playback on the board the left and right channels are occasionally flipped.
<snip>
Has anybody else had this problem, or does anybody have any AT91/Atmel hardware that they could test to see if it occurs on other hardware also?
I have worked with the AT91SAM9260 on a project which is currently suspended (other priorities), where we had a simiar problem, with a codec on SPI. Every time audio was started (capture or playback) the channels could be swapped. Solving that issue remains TODO when we restart.
There was a thread on alsa-devel last month 'Soc Atmel SSC stereo problem' with some suggestions.
In the thread mentioned, Alan proposed me amongst other things to test the LRCK level before starting the SSC. This works well for me. Maybe it should be implemented in a more generic way but the following modification does the trick for me.
in function atmel_pcm_trigger inside file sound/soc/atmel/atmel-pcm.c :
case SNDRV_PCM_TRIGGER_START: +while(!at91_get_gpio_value(AT91_PIN_PB12)); +while(at91_get_gpio_value(AT91_PIN_PB12));
case SNDRV_PCM_TRIGGER_RESUME: +while(!at91_get_gpio_value(AT91_PIN_PB12)); +while(at91_get_gpio_value(AT91_PIN_PB12));
Patrick
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On 11/12/2010 10:52 PM, Irfan Shaikh wrote:
I had faced the similar issue on IMx31. The cause there was reversal of LRCK clock {180 degree phase shift}. probing the LRCK clock may help you to find the problem
From: alsa-devel-bounces@alsa-project.org [alsa-devel-bounces@alsa-project.org] On Behalf Of Patrick Ziegler [patrick.ziegler@fh-kl.de] Sent: Friday, November 12, 2010 1:36 PM To: alsa-devel@alsa-project.org Cc: Ryan Mallon Subject: Re: [alsa-devel] Channel swapping problem on Atmel SSC audio
Am 11.11.2010 13:27, schrieb Alan Horstmann:
On Wednesday 10 November 2010 22:49, Ryan Mallon wrote:
I'm working on a custom board using the AT91SAM9G45 processor and a TLV320AIC26 SPI attached audio codec using I2S format audio. When doing audio playback on the board the left and right channels are occasionally flipped.
<snip>
Has anybody else had this problem, or does anybody have any AT91/Atmel hardware that they could test to see if it occurs on other hardware also?
I have worked with the AT91SAM9260 on a project which is currently suspended (other priorities), where we had a simiar problem, with a codec on SPI. Every time audio was started (capture or playback) the channels could be swapped. Solving that issue remains TODO when we restart.
There was a thread on alsa-devel last month 'Soc Atmel SSC stereo problem' with some suggestions.
Okay, so it's not just me.
In the thread mentioned, Alan proposed me amongst other things to test the LRCK level before starting the SSC. This works well for me. Maybe it should be implemented in a more generic way but the following modification does the trick for me.
in function atmel_pcm_trigger inside file sound/soc/atmel/atmel-pcm.c :
case SNDRV_PCM_TRIGGER_START: +while(!at91_get_gpio_value(AT91_PIN_PB12)); +while(at91_get_gpio_value(AT91_PIN_PB12));
case SNDRV_PCM_TRIGGER_RESUME: +while(!at91_get_gpio_value(AT91_PIN_PB12)); +while(at91_get_gpio_value(AT91_PIN_PB12));
This appears to work, or at least makes the problem much more rare. I'm trying to understand if the problem is a silicon bug in the AT91 hardware, or if the DMA start code in the Atmel SoC driver is buggy.
I'm running with the CPU as the master (generating LRCLK and BCLK) and testing with playback (so CPU is clocking the data out). The TCMR register has the CKS field set to 0x4 (start on falling edge of LRCLK), so the above loops should not be necessary. I suspect that the above fix only makes the problem occur much less frequently, rather than fixing it correctly?
~Ryan
Hi Everyone,
This seems to be very similar to a problem I wrote about this morning and i am wondering if a solution was found?
Thank you, Jason Fox GAI-Tronics Reading PA
On 11/12/2010 10:52 PM, Irfan Shaikh wrote:
I had faced the similar issue on IMx31. The cause there was reversal of LRCK clock {180 degree phase shift}. probing the LRCK clock may help you to find the problem
From: alsa-devel-bounces at alsa-project.org [alsa-devel-bounces at alsa-project.org] On Behalf Of Patrick Ziegler [patrick.ziegler at fh-kl.de] Sent: Friday, November 12, 2010 1:36 PM To: alsa-devel at alsa-project.org Cc: Ryan Mallon Subject: Re: [alsa-devel] Channel swapping problem on Atmel SSC audio
Am 11.11.2010 13:27, schrieb Alan Horstmann:
On Wednesday 10 November 2010 22:49, Ryan Mallon wrote:
I'm working on a custom board using the AT91SAM9G45 processor and a TLV320AIC26 SPI attached audio codec using I2S format audio. When doing audio playback on the board the left and right channels are occasionally flipped.
<snip>
Has anybody else had this problem, or does anybody have any AT91/Atmel hardware that they could test to see if it occurs on other hardware also?
I have worked with the AT91SAM9260 on a project which is currently suspended (other priorities), where we had a simiar problem, with a codec on SPI. Every time audio was started (capture or playback) the channels could be swapped. Solving that issue remains TODO when we restart.
There was a thread on alsa-devel last month 'Soc Atmel SSC stereo problem' with some suggestions.
Okay, so it's not just me.
In the thread mentioned, Alan proposed me amongst other things to test the LRCK level before starting the SSC. This works well for me. Maybe it should be implemented in a more generic way but the following modification does the trick for me.
in function atmel_pcm_trigger inside file sound/soc/atmel/atmel-pcm.c :
case SNDRV_PCM_TRIGGER_START: +while(!at91_get_gpio_value(AT91_PIN_PB12)); +while(at91_get_gpio_value(AT91_PIN_PB12));
case SNDRV_PCM_TRIGGER_RESUME: +while(!at91_get_gpio_value(AT91_PIN_PB12)); +while(at91_get_gpio_value(AT91_PIN_PB12));
This appears to work, or at least makes the problem much more rare. I'm trying to understand if the problem is a silicon bug in the AT91 hardware, or if the DMA start code in the Atmel SoC driver is buggy.
I'm running with the CPU as the master (generating LRCLK and BCLK) and testing with playback (so CPU is clocking the data out). The TCMR register has the CKS field set to 0x4 (start on falling edge of LRCLK), so the above loops should not be necessary. I suspect that the above fix only makes the problem occur much less frequently, rather than fixing it correctly?
~Ryan
Hi,
On 02/17/11 15:45, ext Jason Fox wrote:
This appears to work, or at least makes the problem much more rare. I'm trying to understand if the problem is a silicon bug in the AT91 hardware, or if the DMA start code in the Atmel SoC driver is buggy.
I'm not familiar with the Atmel platform, but we have had similar channel swap/shift problems (random channel swap at stream start) in OMAP3 McBSP. In our case it was due to the fact, that OMAP3 McBSP has two bits to actually enable the digital interface. The early code enabled this two bit at the same time, and that was the root of the problem. This is what happened: - DMA has been configured, and started (HW synchronized DMA, McBSP requests the DMA to push data) - McBSP got enabled, and got released at the same time McBSP immediately signaled the DMA to push data. Depending on the timing, there were cases, when McBSP started to send out the data, while the DMA has not pushed anything to McBSP FIFO. So the first word was 0, and the second was the first word from the sample -> channels swapped. This has happened in McBSP slave configuration as well: depending on the timing of the McBSP start we have seen random channel swap. If the McBSP was enabled just right before the start condition on the I2S bus, it sent out 0 for the first word, and than the audio data -> channel swapped. We have fixed this by first enabling the McBSP, but keeping it unreleased state. When McBSP is enabled, it will trigger DMA to start pushing data, so we have valid audio data in the FIFO. We wait for 500us. We release the McBSP. At this point it will either start listening for the start condition on I2S bus (slave), or start the clocks on the bus. Since we already had the valid audio data in the FIFO, the channel swap has gone.
I suppose you also have similar issue. Other solution which we considered could have been used only in case of 16bit/stereo audio: Configure McBSP for 32bit word length (and single slot) in case of 16bit/streo audio. When the race happens McBSP would have sent 0 for both channels, so we would not have the channels swapped. But this will only work with 16bit/stereo mode - and mono as well ;)
So we sticked with the former solution.
I hope this helps for you to figure out something similar for your problem.
participants (6)
-
Alan Horstmann -
Irfan Shaikh -
Jason Fox -
Patrick Ziegler -
Peter Ujfalusi -
Ryan Mallon