From the perspective your more traditional software programming languages, multi-tasking in SystemVerilog is weird. On one hand, the language includes a special syntax (fork and join) that make it really easy to write code that “runs” in parallel. On the other hand, SystemVerilog “processes” aren’t really processes, or even threads, in the traditional sense. Even if you “get” the SystemVerilog model of cooperative cooperative multi-tasking, there are a number of pitfalls you can run into. One such gotcha that I recently ran into was caused by what appeared to be an innocuous wait fork statement.
Considering SystemVerilog Tagged Unions
I have recently been thinking a lot about tagged unions in SystemVerilog, since I discovered them a few months ago. In this post I present some of the ideal use cases for tagged unions, and why I think no one actually uses them.
Despite being initially proposed in 2003, and officially part of the language since the SystemVerilog 1800-2005 standard was released, at this point tagged unions appear to be a forgotten language feature. I think this is a shame, because since I accidentally ran across the tagged union section of the LRM, I keep thinking of new applications where I would like to make use of them. Don’t get me wrong, there are plenty of reasons that you don’t see tagged unions used in the wild today (language ergonomics, tool support, etc.) but that doesn’t mean they couldn’t have been useful.
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