[alsa-devel] am335x: mcasp in DIT mode

Daniel Mack zonque at gmail.com
Mon Mar 4 09:03:54 CET 2013

On 04.03.2013 08:55, Daniel Mack wrote:
> Hi Vaibhav,
> Hi Yegor,
> On 04.03.2013 07:22, Bedia, Vaibhav wrote:
>> On Fri, Mar 01, 2013 at 16:23:53, Yegor Yefremov wrote:
>>> I've solved the problem with DIT/SPDIF mode (see the issue description
>>> here: http://e2e.ti.com/support/arm/sitara_arm/f/791/p/247447/870030.aspx).
>>> In davinci_mcasp_hw_params() the DIT or I2S params will be set in the
>>> beginning. DIT mode configures the DAVINCI_MCASP_TXMASK_REG and
>>> And here comes the problem:
>>> at the end of davinci_mcasp_hw_params() the
>>> davinci_config_channel_size() will touch the same registers again and
>>> thus overwrite the settings necessary for DIT. After I commented this
>>> routine I got the sound over S/PDIF and sii9022a HDMI transmitter and
>>> I could see the proper bits appearing on my oscilloscope.
>>> What were the best way to solve this problem?
>>> 1. execute  davinci_config_channel_size() only if not in DIT mode?
>>> 2. for DIT only change the DAVINCI_MCASP_TXMASK_REG according to channel width?
>>> 3. execute
>>> if (dev->op_mode == DAVINCI_MCASP_DIT_MODE)
>>>                 davinci_hw_dit_param(dev);
>>> else
>>>                 davinci_hw_param(dev, substream->stream);
>>> after davinci_config_channel_size()
>> AFAIK DIT mode was working on Davinci platforms some time back. Since AM335x
>> has the same hardware block I was surprised to see this bug report. Not having
>> a setup handy to test out DIT related changes, I looked at the commits on the
>> mcasp file to figure out what happened. I suspect one of the recent patches which
>> added 24bit support inadvertently broke the DIT support. Would it be possible
>> for you to do a git-bisect to find out what change it was? It would be good
>> to reference that change in the final patch.
> I agree, but I also believe it's not easy to do, given the number of
> different trees you need for AM33xx support in general.

Just to be clear: I was referring to the number of commits in different
areas that you needed by the time these mcasp patches were merged. I
think they make it tricky to bisect back from the current state now. But
maybe Yegor's setup looks differently, who knows.


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