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Xilinx Quiz: 150/3 = ?

Quiz:

what is DCM CLKFX output frequncy if the CLKFX Divisor is set to 3 in MHS file and input clock is 150MHz?

snippet from MHS file

-------------------- BEGIN dcm_module PARAMETER C_CLKFX_DIVIDE = 3 ... END

--------------------

Answer:

DCM FX output will be 200MHz because the CLKFX multiply default value is 4 ! When the FX multiply is set to default then the multiply parameter is not present in the MHS file, and without knowing the default or using the GUI to view the parameters its really hard to guess. unless you just know.

Antti

Reply to
Antti
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recently I had xst misunderstand

generic ( K1 : std_logic_vector(19 downto 0) := x"3eeee"; );

...

constant K2 : std_logic_vector(19 downto 0) := not (K1) + 1;

somehow K2 ended up being incorrect ... while modelsim did it like I expected it.

constant K2 : std_logic_vector(19 downto 0) := x"00000" - K1;

works fine ...

Antti wrote:

Reply to
Sylvain Munaut

XST probably should misunderstand that.

Which non-standard library is XST using for arithmetic on std_logic_vector, and is Modelsim using a different one?

Now if XST and Modelsim disagreed on results using either signed or unsigned type from numeric_std, it would be worth worrying about.

- Brian

Reply to
Brian Drummond

For a +1 operation there is not much that can fail ... Doesn't matter what the vector represent, I expect a +1 to add 1 at the lsb ant that's what it does usually ...

Sylvain

Reply to
Sylvain Munaut

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