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Associate II
August 8, 2017
Solved

How to feed both i2s channel with DMA

  • August 8, 2017
  • 5 replies
  • 1387 views
Posted on August 08, 2017 at 16:55

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    Best answer by ad ho
    Posted on August 14, 2017 at 14:30

    Okay, I found the mistake, I was expecting my DMA to be 16bits as I programmed i2s so, and did not see that data bit was actually in word. I have been confused as this parameter is not in the main and forgot about it.

    5 replies

    waclawek.jan
    waclawek.jan
    Super User
    August 8, 2017
    Posted on August 08, 2017 at 17:58

    I2S naturally contains both channels so there's something wrong in your setup.

    Observe WS versus CK directly on the codec's pins.

    JW

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    ad hoAuthor
    Associate II
    August 9, 2017
    Posted on August 09, 2017 at 09:22

    Hi Jan,

    Yes you are right, the fact that make me think that it is a software issue is that I checked the I2S bus with a logic analyser. WS is correctly balancing left right, CK is much faster as expected and the data is corresponding to the analog value -> right a nice sinus, left wierd semi periodical signal.

    But what I don't understand, if we take the problem reversly, if I had to send two different signal on the two channels, how would I proceed? 

    In 

    HAL_I2S_Transmit_DMA(&hi2s2, (uint16_t*) sine_table, 512); I don't see any reference about the second channel, is it suposed to be in the sine_table? I tried to put [sin0, 0, sin1, 0, sin2, 0] as if the data where [L0, R0, L1, R1, ...] but then the right channel was not clean anymore.

    I think I have not totally understood the concept...

    waclawek.jan
    waclawek.jan
    Super User
    August 9, 2017
    Posted on August 09, 2017 at 11:12

    I tried to put [sin0, 0, sin1, 0, sin2, 0] as if the data where [L0, R0, L1, R1, ...]

    Yes that's exactly how are they supposed to be.

    but then the right channel was not clean anymore.

    This is why I say something is wrong in your setup. Is the CODEC set properly for I2S/Philips? FMT pin?

    CK is much faster

    Is it exactly 16 x WS?

    JW

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    ad hoAuthorBest answer
    Associate II
    August 14, 2017
    Posted on August 14, 2017 at 14:30

    Okay, I found the mistake, I was expecting my DMA to be 16bits as I programmed i2s so, and did not see that data bit was actually in word. I have been confused as this parameter is not in the main and forgot about it.

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