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use of is_relevant() in sequences

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Hi, I recently ran into an issue related to the use of is_relevant() from within a sequence and I'd like to get some opinion on possible solutions.

Problem: I want to use is_relevant() as a form of back-pressure to stall the enclosing sequence upon some condition. However, that condition is not known until the current item has been generated. Since 'do' is an atomic action, and is_relevant() does not allow access to the generated item as it's being 'do'ne, I'm stuck.

We eventually ended up replacing the 'do' syntax with our own macro for doing an item. Our macros would generate the item first, set some conditions based on the results of the gen, and then invoke 'do' to pass it the item we just generated. The conditions we set right after the gen would be used to implement is_relevant().

The work-around solves the problem, but it's cumbersome and we might run into some issues in the future should the semantics/implementation of 'do' change.

Has anyone else ever encountered a similar problem/limitation with is_relevant()?

cheers,

Joseph H. Zhang
Lead Verification Engineer
Cisco Systems, Inc.
(919) 392-1350


Originally posted in cdnusers.org by jhzhang
Parents

  • Hello Joseph,

    You can do couple things; you can pre-generate the field of the do item or do item's field within is_relevant method, decide to start upon the generated value
    pseudo code may look like

    struct vr_pcie_tlp_pkt {
    tlp_type: tlp_type_t;
    tc: tc_t;
    };

    sequence vr_pcie_tl_seq {

    !pre_tc: tc_t;

    body()@driver.clock is {
    do pkt keeping {
    .tc == pre_tc;
    };
    };

    is_relevant():bool is {
    gen pre_tc;
    return TRUE(tc in [0..3] and tc_pipe_is_empty);
    };
    };






    Originally posted in cdnusers.org by levent
Reply

  • Hello Joseph,

    You can do couple things; you can pre-generate the field of the do item or do item's field within is_relevant method, decide to start upon the generated value
    pseudo code may look like

    struct vr_pcie_tlp_pkt {
    tlp_type: tlp_type_t;
    tc: tc_t;
    };

    sequence vr_pcie_tl_seq {

    !pre_tc: tc_t;

    body()@driver.clock is {
    do pkt keeping {
    .tc == pre_tc;
    };
    };

    is_relevant():bool is {
    gen pre_tc;
    return TRUE(tc in [0..3] and tc_pipe_is_empty);
    };
    };






    Originally posted in cdnusers.org by levent
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