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AM335x mapping PCM channels to TDM slots in McASP

Shahram Shabpareh
Prodigy 130 points


Hi

We have a specific configuration for McASP0. We have 32 tdm slots and 32 PCM channels and each slot is 8 bit. we want that channel 1 to be mapped to slot 1, channel 2 be mapped to slot 2, .... channel 32 mapped to slot 32. but when i run aplay to send to only channel 1, data will be send to all slots! i want that all slots be 0 except slot 1. How can i do that?

I'm using linux kernel 3.2.0 and searched in source tree and found snd_soc_dai_set_channel_map function, but there is no code for it in davinci-mcasp.c file.

I will be really thankful if anyone can help me.

  • 0
    TI__Guru**** 393215 points
    I will forward this to the software team.
  • 0
    TI__Guru**** 161600 points
    Hi,

    You need to define the unsigned int channel_map[8] = {0, 1, 2,........}; in the hw_params function.
    Then you need to call the set_channel_map function, something like:
    ret = snd_soc_dai_set_channel_map(cpu_dai, X, channel_map, X channel_map) //X denotes the number of channels slots.

    You could take a reference from the following mailthread as a reference: mailman.alsa-project.org/.../021159.html
    NOTE that the above link is for a different device, but you could use the logic to modify your code to use snd_soc_dai_set_channel_map().

    Best Regards,
    Yordan
  • 0 in reply to Yordan Kovachev
    Prodigy 130 points

    Yordan Kovachev said:
    Hi,

    You need to define the unsigned int channel_map[8] = {0, 1, 2,........}; in the hw_params function.
    Then you need to call the set_channel_map function, something like:
    ret = snd_soc_dai_set_channel_map(cpu_dai, X, channel_map, X channel_map) //X denotes the number of channels slots.

    You could take a reference from the following mailthread as a reference: mailman.alsa-project.org/.../021159.html
    NOTE that the above link is for a different device, but you could use the logic to modify your code to use snd_soc_dai_set_channel_map().

    Best Regards,
    Yordan

    Hi

    I found that set_channel_map function is not required in my case, because i don't want to change mapping of pcm channels and tdm slots. the function that i need is copy that is defined in snd_pcm_ops structure. I defined a function called davinci_pcm_copy in davinci-pcm.c file and added a line like below:

    static struct snd_pcm_ops davinci_pcm_ops = {

    ....

    .copy = davinci_pcm_copy,

    };

    the problem is, copy function not called at all because the format of my file is mu_law.

    when i use aplay command this format is handled by pcm_plugin and pcm_mulaw functions in alsa-lib that have different way in alsa-lib and kernel and if i want to copy function in kernel being called i should use standard wav format that uses pcm_hw in alsa-lib.

    How can i resolve this issue?