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C641x: HPI16 vs HPI32 selection

Victor Kazmirenko
Guru 13202 points

Hello,

I'm in a doubt about HPI width configuration. As per SPRS226M, HD5 is specified as configuration pin:

0 − HPI operates as an HPI16. (HPI bus is 16 bits wide. HD[15:0] pins are used and the remaining HD[31:16] pins are reserved pins in the Hi-Z state.)
1 − HPI operates as an HPI32. (HPI bus is 32 bits wide. All HD[31:0] pins are used for host-port operations.)

Later it is said that there is no internal pulling resistor on HD5 pin:

internal pullup/pulldown resistors exist on these pins (except for HD5/AD5)

And later:

Host-Port bus width user-configurable at device reset via a 10-kΩ resistor pullup/pulldown resistor on the HD5 pin

So do I understand correctly, that among all HD lines HD5 is special. I mean that All HD lines connected directly between DSP and host processor, but HD5 has one extra connection in the middle between DSP and host (like on attached picture), and that connection through 10 kOhm resistor defines port width. Is this correct?

Thanks in advance.

  • 0
    TI__Guru* 84110 points

    If PCI_EN=0, then you must have a 10-kOhm resistor either pulling HD5 high or low depending on the configuration you want to use.

    Your understanding does seem to be correct, but I do not want to reword what is in the datasheet. The datasheet's explanation is the final word, and there does not appear to be a conflict between any of the statements you have pulled from it.

    Your picture is correct for HPI32 operation. It shows a single pull-up resistor on HD5.

    Regards,
    RandyP

  • 0 in reply to RandyP
    Guru 13202 points

    Hello RandyP,

    Thank you for quick response.

    I was a bit curious about described operation mode. I mean that configuration resistor connected to the data line, not dedicated config pin. As you mentioned, there is no contradiction in data sheet citations, I did not meant it. Just I wanted to make sure I got the idea right. Perhaps, resistor leakage is smaller than normal operation currents, so it does not affect normal operation of the bus, but still enough for DSP to sense configuration level at reset time.

    And one more question. You wrote:

    RandyP said:
    If PCI_EN=0, then you must have a 10-kOhm resistor

    Do you mean, that HPI peripheral is mutually exclusive with PCI, so when PCI_EN = 1, then there is no reason to have this resistor on PCI bus?

    Anyway, I am using C6414 now, it has no PCI, so PCI_EN is internally pulled down. But we have C6416 devices as well, so I want to be sure.

  • 0 in reply to Victor Kazmirenko
    TI__Guru* 84110 points

    There are multiple functions available on some pins, including the HPI bus. The PCI and HPI are shared on the same pins, so only one of those functions can be selected. There are also some GPIO pins that can be shared on some of these same pins.

    Regards,
    RandyP