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LP-AM243: QSPI, External Loopback, and Errata i2307

Joe Paolino
Intellectual 470 points
Part Number: LP-AM243
Other Parts Discussed in Thread: SYSCONFIG

Hello,

I'm trying to understand the implementation of the LP-AM243 QSPI and how it adheres to Errata i2307.  The LP has implemented External Board Loopback.  The "Workaround" in i2307 says that the "design must not use External Board Loopback if planning to use OSPI as a boot source."  I understand that the Boot ROM only uses internal loopback and that other clock topologies can be used after boot.

I'd like clarification on "must not use External Board Loopback" because the LP-AM243 has apparently been implemented with it.

Has the LP-AM243 been able to get around this requirement by ensuring the propagation delay of OSPI0_Clk is <450pS?

Lastly, does Errata i2189 come into play with External Board Loopback because LBCLK routes into DQS? Or does it only apply to true DQS Mode combined with Octal SPI Flash containing a DQS Output?

Thanks very much,

Joe

  • 0
    TI__Expert 3140 points

    Hi Joe,


    Started looking into it and will come with initial response by 25/09/2023.


    Thanks & Regards,
    Rijohn

  • 0
    TI__Expert 3140 points

    Hi Joe,

    We have implemented QSPI in LP-AM243.
    DQS is only available in OSPI devices. In LP-AM243, since it is only QSPI interfacing, the OSPI0_DQS to OSPI0_LBCLK connection is not significant.
    Section 9.2.3.3 in AM243 datasheet (www.ti.com/.../am2434.pdf) has a detailed explanation about usage of DQS in Octal SPI devices.


    Regards,
    Rijohn

  • 0 in reply to Rijohn Pius
    Intellectual 470 points

    Thanks Rijohn.  Can you expand on what you mean that the LBCLK to DQS is not significant?  From reading datasheet at 9.2.2.2 and the SDR timing at 7.10.5.14.1.2.1, there's a noticeable difference in setup and hold performance when using external loopback mode. In QSPI mode, the DQS input is required to achieve that improved performance.

    Another confusing aspect is the generic reference to OSPI in the errata and elsewhere.  OSPI can be referring to the peripheral itself (which is capable of QSPI, SPI) or OSPI is the protocol which uses 8 databits and DQS.  The picture below seems to broadly apply to OSPI, QSPI, and SPI, which operate from the OSPI peripheral.

    I really just need to understand how the LP-AM243 does not violate Errata i2307.  Thank you

  • 0 in reply to Joe Paolino
    TI__Expert 3140 points

    Hi Joe,

    Sorry for the delay.
    I will get back to you as soon as possible after discussion with the experts.

    Can you please ensure if this reference provided (reading datasheet at 9.2.2.2) is correct?

    Regards,
    Rijohn

  • 0 in reply to Rijohn Pius
    TI__Expert 3140 points

    Hi Joe,

    We have implemented QSPI in LP-AM243.

    According to Errata i2307, boot happens only by internal loopback mode.

    From Pin Attributes session it is evident that OSPI0_LBCLKO has 2 modes of functionality.
    mode 0 : OSPI0_LBCLKO
    mode 7 : GPIO_1

    In LP-AM243 we have set pin OSPI0_LBCLKO with GPIO functionality.
    Although the schematic shows an external loopback connection, there is no actual connection between OSPI0_LBCLKO and OSPI0_DQS.

    NOTE: OSPI0_LBCLKO pin is locked in SYSCONFIG of LP-AM243.

    Lastly, Errata i2189 is applicable for both External Board Loopback and True DQS mode.

    Thank you for directing us to TRM. We are currently looking into that statement that says that no traces must be on LBCLK for internal loopback to work.

    Regards,

    Rijohn

  • 0 in reply to Rijohn Pius
    Intellectual 470 points

    Thank you, Rijohn.  Please confirm/correct my summary:

    • During Boot, only internal loopback is supported for QSPI and OSPI due to Errata i2307
    • During Normal Operation, External Loopback for QSPI is not recommended because of i2189
  • +1 in reply to Joe Paolino
    TI__Expert 3140 points

    Hi Joe,

    During Boot, only internal loopback is supported for QSPI and OSPI due to Errata i2307.

    Usage of External Loopback for QSPI during normal operation depends on the application which you are implementing.

    If you are using External loopback , ensure errata i2189 is followed (PHY tuning algorithm). Otherwise, you can use internal clock mode only.

    Thanks & Regards,

    Rijohn