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In DSP/BIOS how does it select input frequency for CLK module

David Rowley
Prodigy 100 points

We are using DSP/BIOS, not SYS/BIOS and if I right clock on "CLK - Clock Manager" I get the window below and grayed out is "Input Frequency (MHz) 24.0000"

And I can't figure out where it gets the value of 24.0000 to use when I edit the TCF file. How does it know to use that value?

This sets up a CLK object of PRD_clock because for the PRD module the check box of "USE CLK manager to drive PRD" is checked.

  • 0
    TI__Guru** 116100 points
    Hi,
    In *.tcf file, you can see the "bios.CLK.INPUTCLK" variable to use that clock.
    If not, change that value, you may get it in *.tcf.
    By default, you could see that 24MHz value depends on processor.
  • 0
    Prodigy 100 points
    I'm starting to see that 24 MHz is a sort of default value and it doesn't work quite like you say. The value "bios.CLK.INPUTCLK = XX" does not show up in the .tcf file until the check box to specify clock is selected. Then it will add "bios.CLK.SPECIFYRATE = 1" to the .tcf file and then I can set the input frequency to 21.0000 and I see in the file bios.CLK.INPUTCLK = 21.0000.

    Then I uncheck the box to specify the input clock and in the .tcf file I see "bios.CLK.SPECIFYRATE = 0" and I still see "bios.CLK.INPUTCLK = 21.0000" but "bios.CLK.INPUTCLK = 21.0000" is no longer used because the last line in the .tcf file is bios.CLK.SPECIFYRATE = 0 and with that the INPUTCLK becomes the default of 24 MHz and "bios.CLK.INPUTCLK = 21.0000" is in the file but not used because of the order of that line and the "bios.CLK.SPECIFYRATE = 0" line.

    And if the input clock is never changed then the line "bios.CLK.INPUTCLK = " never shows up in the .tcf file and the default value of 24 MHz is used even thought the file has no explicit "bios.CLK.INPUTCLK = XX".

    So now I see why I couldn't find "24" anywhere, because it picks it as a default and that is buried in the tool somewhere.