i.MX8MM EVK MICFIL<==> PDM MiC issues

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i.MX8MM EVK MICFIL<==> PDM MiC issues

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sreedhar_appala
Contributor III

Hi,

We are working with i.MX8MM EVK + i.MX 8MIC-RPI-MX8 Board.

i.MX 8MIC-RPI-MX8 Board is interfaced to i.MX8MM EVK through MICFIL (PDM) interface.

when we try do recording for samplerate 48kHz. we are observing overruns.

But when we do recording for samplerate 16kHz , no overruns observed.

Could you please clarify me below questions:

1. SAI and MICFIL are different interfaces in i.MX8MM or MICFIL (PDM) interface is part of SAI

2. MICFIL (PDM Microphone interface) Can support upto what sample rates?

Thank you, Sreedhar

@Igor 

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igorpadykov
NXP TechSupport
NXP TechSupport

Hi Sreedhar

 

1. they are different

2.  sample rate is programmable and described in Reference Manual, as for

hardware capability per sect.3.9.8 PDM timing parameters

i.MX 8M Mini Applications Processor Datasheet for Consumer Products

"PDM clock operative range is from 500 kHz to 6 MHz."

Linux PDM driver is described in sect.7.6.4 Software Overview  i.MX Linux Reference Manual​

"The captured audio format is 8-channels 32-bit wide linear PCM audio data @ 48kHz or 44.1kHz rate."

It can be tested with unit test:

https://source.codeaurora.org/external/imx/imx-test/tree/test/mxc_pdm_test?h=imx_5.4.47_2.2.0

 

Best regards
igor

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igorpadykov
NXP TechSupport
NXP TechSupport

Hi Sreedhar

 

1. they are different

2.  sample rate is programmable and described in Reference Manual, as for

hardware capability per sect.3.9.8 PDM timing parameters

i.MX 8M Mini Applications Processor Datasheet for Consumer Products

"PDM clock operative range is from 500 kHz to 6 MHz."

Linux PDM driver is described in sect.7.6.4 Software Overview  i.MX Linux Reference Manual​

"The captured audio format is 8-channels 32-bit wide linear PCM audio data @ 48kHz or 44.1kHz rate."

It can be tested with unit test:

https://source.codeaurora.org/external/imx/imx-test/tree/test/mxc_pdm_test?h=imx_5.4.47_2.2.0

 

Best regards
igor

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sreedhar_appala
Contributor III

Thank you Igor!!

From :

https://source.codeaurora.org/external/imx/imx-test/tree/test/mxc_pdm_test/README?h=imx_5.4.47_2.2.0

From the README document: 

"Alsa tool to capture raw PDM data from input mic over SAI interface"

MICFIL uses SAI interface?

Could you please clarify, this is confusing to me.

Thank you, Sreedhar

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igorpadykov
NXP TechSupport
NXP TechSupport

Hi Sreedhar

 

>"Alsa tool to capture raw PDM data from input mic over SAI interface"

>MICFIL uses SAI interface?

 

MICFIL captures audio data and sends to SAI module, they are different modules.

 

Best regards
igor

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sreedhar_appala
Contributor III
 
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