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SATA Input Clock

Inderjit Bains
Expert 2745 points

In TMS320C674x/OMAP-L1x Processor Serial ATA (SATA) Controller:  section 2.1 states that the input clock should be between 75MHz and 375 MHz.  However, Table 1 shows a multiplier of 25x being valide, which would allow a clock of 60 MHz.  Which one is correct?

  • 0
    TI__Expert 7435 points

    Inderjit,

    One option is to refer to the schematics of TI EVM/Hawkboard for SATA.

    regards

    swami

  • 0 in reply to swami
    Expert 2745 points

    There is a reason I'm asking:  a 60 MHz solution is available; 75 MHz and 100 MHz are special-order.  The Logic PD schematic uses a solution that is too expensive.  I'm not familiar with the Hawkboard.

  • 0
    TI__Expert 5475 points

    Hi,

    Actually, the 25x multiplier value is for a 62.5MHz clock source, still custom. We have not tested it for a 60MHz input clock with 25x multiplier. It most likely would work well. However, this is not a good enough reason for us to suggest for you to use it.

    We will think about how to address the multiplier value. We probably need to remove that multipler value or add a 62.5MHz input clock option corresponding to 25x multiplier value.

    Best regards, Zegeye

     

  • 0 in reply to Zegeye Alemu
    Expert 2745 points

    62.5 MHz * 25 = 1.5625 GHz, not 1.5 GHz.

  • 0 in reply to Inderjit Bains
    TI__Expert 5475 points

    Hi,

    That is correct, 62.5MHz x 25 is > 1.5GHz. We tell customer to use a clock source that would generate a 1.5GHz clock.

    However, in this case, the solution would work too. Just to give you a bit of a reason why the 62.5MHz option was an interest to us was that we were trying to generate a 3.125GHz clock (via x50 multiplier value) and that was the reason why.

    Regardless, this 62.5MHz clock source is not a good solution for you since it still requires a custom clock source.

    For this reason, and for the reason that the x25 multiplier value does not generate an exact 1.5GHz value, we will remove this multiplier value to not cause any more confusion on the next release.

    Thanks for bringing this issue up so that it is corrected in the future.

    Best regards, Zegeye

  • 0 in reply to Zegeye Alemu
    Expert 2745 points

    But 60Mhz * 25 is 1.5GHz exactly, and 60 MHz is a standard frequency.  If the x25 multiplier works, why de-feature it?

  • 0 in reply to Inderjit Bains
    TI__Expert 5475 points

    Hi,

    We have not characterizd the SATA Subsystem operation for that combination of clock frequency (input 60MHz and output 1.5GHz). There are many design reasons why. It is not that simple and that direct. You are only obseving the functional clock frequency not the input clock frequncy. We only gurantee what we have characterized. The x25 multiplier option was not being used for a 60MHz input clock. We do understand that custom solutions are expensive and would like to use off the shelve components for cost reasons. In order to do that, we will have to ovecome the design challenges. We plan to do that in the future.

    Bottom line is that even though we require exact 1.5GHz clock for an input clock frequency of 62.5MHz one can use a x25 multiplier value and the resultant clock frequency 1.5625 GHz would also work. Similarly even though a 60MHz input clock results with a 1.5GHz functional clock frequency, we have not characterized this particular input frequncy (60MHz) and its resultant frequency combination and can not guarantee the functionality of the entire device. Since we are aware of the challenges, we would have been the first to recommend for its use if it was that direct. But we can't.

    I guess, I created more confusion than solution. I was trying to give you reasons why the x25 multiplier value was present in the table and it has a meanigful reason for its presence. Sorry for the confusion.

    Assume that the x25 multiplier option is captured by mistake and does not apply. The future table will not have this multiplier value.

    Hope this helps.

    Best regards, Zegeye