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C6670: Is FFTC output scaling applied to dynamic scaling?

Chen Neville54361
Intellectual 315 points

Hi all,

in KeyStone FFTC UG(SPRUGS2B, http://www.ti.com/litv/pdf/sprugs2b) Page 20, "The engine supports two modes of scaling applied to each stage, static scaling and
dynamic scaling. Output scaling only supports static mode.". From this sentence, my understanding is that output scaling is only applied to static scaling. When using dynamic scaling, the output scaling doesn't work. But in page 66 Table 9-17, for field "OUTPUT_SCALING", note #1(These fields are used only in ‘Static’ scaling mode) is applied to it. This note is applied to fields "STAGE_x_SCALING". Here it makes me a little confusing. Does it mean that "OUTPUT_SCALING" is applied to dynamic scaling? This is conflict to the sentence in page20. Does anyone know whether output scaling is applied to dynamic scaling? Thanks a lot.

Best regards,

Neville Chen

  • 0
    TI__Genius 12135 points

    Hi,

       The "OUTPUT_SCALING" WILL be applied to the data in both static and dynamic scaling modes. The 'Output scaling' on Page 20 was meant to refers to the "output stage scaling" (STAGE_OUT_SCALING).  This statement does look ambiguous and will be addressed in the next release of the user guide.

    Regards,

    Sudhanand.

  • 0 in reply to Sudhanand Dayalan
    Intellectual 315 points

    Thanks Sudhanand.

    We are using dynamic scaling and OUTPUT_SCALING is set as 0x80 (i.e. = 1). And we connect FFTC to AIF2 directly without any CPU intervention for CPRI mode. Since FFTC have dynamic scaling to the input, to make the fix scaling to the input, we can use "block exponent" reported by FFTC to conpensate the dynamic scaling. But in FFTC-AIF2 direct connection mode, how can we achieve this? Do you have any good suggestion? Thanks a lot.

    Best regards,

    Neville Chen

  • 0 in reply to Chen Neville54361
    TI__Genius 12135 points

    Hi Neville,

     For downlink, it is recomended that 'Static Scaling' be used since the AIF2 expects its input data to have a constant gain across symbols.

    Regards,

    Sudhanand.