Re: Signal/Variable Initial Vaues and Evils of Asynchronous Reset

Discussion in 'VHDL' started by Mike Treseler, May 29, 2010.

  1. Wendigo wrote:

    > "When you give a register an initial value in a declaration, XST sets this
    > value on the output of the register at global reset, or at power up. The
    > assigned value is carried in the NGC file as an INIT attribute on the
    > register, and is independent of any local reset."
    >
    > Are there certain vendors that don't support this? Is it not
    > supported by certain technologies? (ASICs, perhaps?)


    That is how brand X does it.
    Keep in mind that an FPGA doesn't do anything
    at power up until the image is successfully loaded,
    and even then, a "non-evil" synchronous reset won't do
    anything until the clock is running.

    > Can the GSR signal (Global Set/Reset, I'm guessing this is a
    > vendor-specific term) be used for synchronous reset?


    No. It is brand X only, and isn't an input.
    Better than nothing, but not often adequate.

    -- Mike Treseler
     
    Mike Treseler, May 29, 2010
    #1
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