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AM62P: AM62P MCASP lines query

ROSHAN RAJAGOPAL
Intellectual 365 points

Part Number: AM62P
Other Parts Discussed in Thread: LMK1C1104, TXB0104

Hi , 

I was reviewing the evaluation board schematic and noticed a few points that I would like to clarify.

From my understanding, the design allows us to select either the codec or the HDMI audio path to the processor, while the same I²S line is also tapped to the Bluetooth module. My questions are as follows:

  1. Will the processor be able to drive both the Bluetooth output and the codec/HDMI output simultaneously?

  2. In the case where both the Bluetooth and codec/HDMI provide microphone input(different audio) at the same time, will the processor be able to differentiate between them?

  3. When cascading these lines, up to how many devices can be supported reliably ?


image.png

Regards, 
Roshan Rajagopal 

  • 0
    TI__Intellectual 1580 points

    Hello Roshan,

    1. The codec and HDMI paths are selected through the mux, while Bluetooth is connected through a separate buffered path. Bluetooth and HDMI/Codec can be connected at the same time. However, since they share the same McASP1 data signals, they cannot have independent streams using this routing. 

    2. On the receive side, Bluetooth and the Codec share the MCASP1_AXR2. They should not drive the signal simultaneously, and the processor cannot distinguish two simultaneous input streams on the same serializer. Note that the HDMI path on this EVM does not provide an audio input back to the SoC.

    3. We do not recommend cascading/fly-by routing topology when sharing a McASP clock across multiple devices due to potential signal integrity concerns. We recommend a clock fanout buffer, like the LMK1C1104, for such use cases.

    Regards,
    Karam 

  • 0 in reply to Karam Haddad
    Intellectual 365 points

    Hi Karam,
    I have some clarifications:

    1. Do you mean that output from processor( say audio music) will be shared between both the HDMI/codec and bluetooth?? but we wont be able to control the codec/HDMI and bluetooth independently?
    2. Here we are saying the mic from the bluetooth and the codec should not drive at the same time on the MCASP1_AXR2 line, if that happens then the signal might get distorted or even lost?
    3. Here you have recommended us to use a clock buffer but in the evm schematic the clock is cascaded right , it just goes through a level shifter and into the bluetooth line.

    Regards,
    Roshan Rajagopal

  • 0 in reply to ROSHAN RAJAGOPAL
    TI__Intellectual 1580 points

    Hi Roshan,

    1. With the way the EVM is routed in this specific example HDMI/Codec and Bluetooth share MCASP1_AXR0 for TX, so they will receive the same audio stream. Independent simultaneous streams would require using separate McASP AXR serializers.
    2. McASP1_AXR2 should be driven by one source at a time. Doing it simultaneously might cause contention on the line and other possible issues.
    3. The EVM is using the TXB0104 level shifter, which is also an active buffered translator that re-drives the signal.

    Regards,
    Karam

  • 0 in reply to Karam Haddad
    Intellectual 365 points

    Hi Karam,

    Thank you for sharing the details. Your explanation has been very helpful in clarifying our queries and addressing our doubts.


    Regards,
    Roshan Rajagopal

  • 0 in reply to ROSHAN RAJAGOPAL
    TI__Intellectual 1580 points

    Hi Roshan,

    Thank you for the kind words! I will now close this thread.

    Regards,
    Karam