-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 [EMAIL PROTECTED] wrote:
|> Since the tests seem to be using blocking rather than non-blocking assigns |> there really shouldn't be a scheduling issue - i.e. blocking assigns |> should just be executed immediately rather than scheduled, so the Verilog-XL |> looks like the right behavior to me. The comment in sched2.v about the |> "& gate" is bogus because there is no and gate only a logical operation |> (with no delay), and the LRM says the LHS is assigned when the RHS changes |> for a continuous assign. There is a sublety here, in that the expression of a continuous assign is interpreted at least as a single gate. It must be, in order to give it a driver. Notice that continuous assignments can have strength and propagation times. | From a performance perspective you don't want to schedule anything if you |> don't have to since that's extra overhead - so the XL behavior is preferable. |> Also, spliting the assignment over delta cycles (or at least making it |> non-atomic) is more likely to cause race conditions. It doesn't necessarily turn out to be so. For example, if the thread is writing all the inputs to a complex expression and netlist of gates, it could save many evaluation steps overall to schedule them instead of push them. John S. experienced that to be so, and given what I'm seeing in my fiddling, I also believe it to be likely so. |> Actually it's pretty unreasonable that there is such a disparity on |> these simple cases. It is *reasonable*, because these cases have races and are therefore by some measures not reasonable Verilog in the first place. They remain in the ivtest suite because they do reflect the marginal behavior of certain tools. |> I think there is a problem in that there is no official "reference" |> simulator to defer to for the "correct" result - an exercise for someone |> in academia perhaps. XL is, theoretically, that reference, although that's for IEEE1364-1995 and not the -2001 standard. That said, XL seems to be alone on the particular scheduling issue that these tests bring up, and at this point I doubt even Cadence cares. - -- Steve Williams "The woods are lovely, dark and deep. steve at icarus.com But I have promises to keep, http://www.icarus.com and lines to code before I sleep, http://www.picturel.com And lines to code before I sleep." -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.5 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFCwZSErPt1Sc2b3ikRAhZFAKDbpcBQwKFQCnP+56bKYW4Ia8gC+gCgzBj5 /maLwrtGUXGVWAZ3L6v8cEM= =iC+Y -----END PGP SIGNATURE-----
