Re: udp scheduling semantics

From: Clifford E. Cummings (cliffc@sunburst-design.com)
Date: Thu Sep 11 2003 - 14:49:20 PDT

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    Hi, Shalom -

    At 05:57 PM 9/11/03 +0300, Shalom Bresticker wrote:
    >Precedence: bulk
    >
    >Where are the UDP scheduling semantics described, especially for sequential
    >udp's?

    UDP scheduling semantics are not described and they have been implemented
    differently by different vendors. In my opinion, combinational UDPs should
    be scheduled into the Active Events Queue and sequential UDPs (any UDP that
    has a reg declaration) should be scheduled the same as nonblocking
    assignments; that is, the inputs should be evaluated in the Active Events
    Queue and the output should be scheduled into the Nonblocking Update Events
    Queue. This is the how we can guarantee that a pipeline of UDP flip-flops
    simulates like the RTL and like real hardware.

    I think the last time I checked, VCS and Verilog-XL simulated as described
    above and ModelSim and NC-Verilog had races (did all scheduling in the
    Active Events Queue), but it has been a while since I ran this test.

    Regards - Cliff

    >I thought I had seen them once, but I cannot find them,
    >and I am no longer sure they are really described.
    >
    >--
    >Shalom Bresticker Shalom.Bresticker@motorola.com
    >Design & Reuse Methodology Tel: +972 9 9522268
    >Motorola Semiconductor Israel, Ltd. Fax: +972 9 9522890
    >POB 2208, Herzlia 46120, ISRAEL Cell: +972 50 441478

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