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AM620-Q1: McASP loopback

one and zero
Mastermind 18256 points

Part Number: AM620-Q1

Tool/software:

Dear Champs,

As far I know, the PCM audio stream from the external SXM tuner is connected to some MCASP input. The related wordstrobe (48kHz) and clock signal

is provided by the ethernet PHY. This clock is derived/sync with the recovered media clock. The sample rate converter embedded in the SXM module

is used from any sample rate drift compensation. This sound input stream will be available by some linux ALSA capture device.

 

Additional to that, we want to realize a hardware audio loopback on the same MCASP (green). The output/playback side can be used by writing to an ALSA

playback device. Audio data is looped back to an input pin and can be read by an ALSA capture device.

The speed/rate is sync with recovered media clock too. The SBR tuner, writing to the playback device, can do the required audio sample rate drift

compensation.

This SBR audio loopback shall be useable in parallel to the SXM audio input.

 

  • Is this possible?
  • Is this possible with all MCASP interfaces (0-2)?
  • Please provide details about the required HW pin connection.
  • Is this supported by TI MCASP linux ALSA driver?
  • Any further hints?

 

Is there any limit for the configured ethernet PHY pll clock. How is minimum and maximum audio clock frequency?

 

 

 

 

Thanks ans kind rgeards,

one and zero

  • 0
    TI__Intellectual 1420 points

    Hello one and zero,

    Please allow me some time to look at this and I will get back to you with an update within 2 days.

    Regards, 

    Karam

  • 0
    TI__Intellectual 1420 points

    Hello one and zero,

    Thank you for your patience. Regarding your observations:

    • It is possible to implement, but please refer to the following:
    • It's supported on all McASP's 0-2.
    • Loopback would have to be done on the same McASP and use SYNC mode with any serializer: 
      • If in SYNC mode, the receive clock domain is routed internally to the transmit domain. Therefore, McASP clock should be routed to the transmit side (ACLKX, AFSX).
      • For more information, refer to McASP Design Guide (Figure 13. Clock Generation in SYNC Mode).
    • It is supported by Linux ALSA. SDK Linux for AM62x (3.2.2.1.4 Board-specific instructions section) shows support for applications like simultaneous record and playback. 
    • McASP max audio bit clock frequency is up to 50 MHz.
    • Extra notes:
      • Ensure same audio frame format all throughout, (i.e. audio coming into McASP, and the audio looping back).
      • What Ethernet PHY is being used here?

    Regards,
    Karam