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DM816x SPI boot clk speed

abadobid
Intellectual 300 points

We are using a DM8165 as a pci endpoint booting u-boot from spi flash (spi boot mode).

In order to meet PCI specification, I believe u-boot needs to have the pcie configured within 100ms of reset.  Our u-boot image is approx. 50k in size.  From the 816x trf, spi boot mode should be using a 12MHz clock which should load the image in ~50ms, but it is actually taking ~100ms.

I have looked at the SPI clk rate used by the boot rom, and it looks like it is ~6.6MHz instead of 12MHz as called out in the TRF.

What should the SPI clock rate be for the boot rom?  Is there a way to have a higher clock rate?

  • 0
    Intellectual 300 points

    O.K., I see an errata for this

    http://www.ti.com/lit/er/sprz329d/sprz329d.pdf  advisory 1.1.22 although it doesn't give any details except that there is no workaround.

    So is there a way to have a the DM816x boot from spi and be a pci endpoint?  I'm not sure how small u-boot can be but I imagine probably not much below 50k.  Would this require another boot stage with with a minimal application that would transfer u-boot to on chip memory?  Any examples of something like this?

  • 0 in reply to abadobid
    Guru 31670 points

    I'm not very clear on the limitation of the PCIe timings. Since there is no way to improve the SPI clock, you can try to create a minimal image of u-boot by stripping off most of the commands from it. You can have a very tiny image of around 80-90KB in size or even lesser. 

  • 0 in reply to Renjith Thomas
    Intellectual 300 points

    Hello Renjith,

    That's basically what I ended up doing some time ago.  I ended up creating a very minimal u-boot that is around 40k in size and minimal delays and was able to get it to set up PCIe in around 90ms.


    It just surprises me that I haven't seen others having a similar problem, but maybe the PCIe endpoint is not such a common usecase for the DM816x.

  • 0 in reply to abadobid
    Guru 31670 points

    Glad to know that your problem is resolved.

    You are right. This is not a very common use case for most customers.