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AEMIF boot: clarifications needed

Alexander Khvilivitzky
Expert 1055 points


I have a couple of questions regarding AEMIF boot description in the documentation.

1. SPRUFI1 "AEMIF" on p.34 says: "When executing code from the EMIF, the bus width must be configured to be an 8-bit data bus."

Is that true?  Does it mean that AEMIF boot cannot be performed in 16-bit mode? BTW, if this is true, it would be nice to have it mentioned in the boot description, not buried deep in the EMIF documentation, because this affects the board layout.

 

2. SPRS457C (DM365 datasheet), p.68 claims that EMIF address pins EM_A[15:21] "must be pulled down externally" (because their default function is GPIO). However the same documents states that all those pins have internal pull down resistors. Which of the 2 is true?

 

Thank you.

  • 0
    TI__Expert 5955 points

    Hi,

    1. Because the DM36x does not have the byte enable pins, when executing code from the EMIF, the bus width must be configured to be an 8-bit data bus to handle the 8-bit data type correctly. That also means the AEMIF boot cannot be performed in 16-bit mode. We will have it mentioned in the boot description in the next ARM SS document revison. Thank you very much for your input.

    2. Both of them are true. The state of the internal PU/PD will be unknow until the device is in reset. So you can't rely on the PU/PD being activated until a valid device reset is asserted. Therefore TI recommend to add the external Pull down resistors for this reason.

    Thanks,

    Tai Nguyen 

  • 0 in reply to Tai Nguyen
    Expert 1055 points

    Hi Tai,

    thank you for your response. I'd like to clarify question 2 a bit.

    Are you referring to the power up reset (RESET# pin of the DM365) or some other type of reset, additional to that? I think it's safe to assume that the power up reset is performed always, otherwise we can't really expect the chip to work properly, can we? Since the boot process doesn't start until after the reset is complete, the address pins should be all pulled down by that time with the internal PD's, shouldn't they? Am I missing something here?

  • 0 in reply to Alexander Khvilivitzky
    TI__Expert 5955 points

    Hi Alexander,

    Yes, I was referring to the power up reset (RESET# pin of the DM365). You are correct that the power up reset is performed always for the chip to work properly. Yes, the boot process does not start until after the reset is complete and the address pins should be pull down by that time with the internal PD's. The external PD is recommended to assure the pins being in a known state before the reset is complete.

    Thanks.

    Tai Nguyen