Protect against --protect-lib Verilator runtime incompatibility

[veripoolbot]

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Author Name: Todd Strader (@toddstrader)
Original Redmine Issue: 1518 from https://www.veripool.org

Original Assignee: Todd Strader (@toddstrader)

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Currently all --dpi-protect'ed modules and the top-level design share the same Verilator runtime symbols. Some options which have been suggested so far are:

• Wrap the --dpi-protect'ed modules' runtimes in a unique namespace
• Maintain a relatively stable and versioned Verilator API

[veripoolbot]

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Original Redmine Comment
Author Name: Wilson Snyder (@wsnyder)
Original Date: 2019-09-24T12:16:08Z

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Some items such as the mutexes for multithreading, tracing, VPI name lookup, and coverage are assumed to be common across all Verilated models. Perhaps some can be eliminated but probably not - for example there are only a certain number of physical CPUs so scheduling on more that that will tank performance. Some thought is needed on these.