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chipsalliance / chisel

Chisel: A Modern Hardware Design Language
https://www.chisel-lang.org/
Apache License 2.0
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Some recommendations on stop #1521

Open davidmlw opened 4 years ago

davidmlw commented 4 years ago
  1. Add stop(code: UInt): Unit. I am not sure whether it is possible. It could be more useful if stop can pass the internal circuit state outside.
  2. Add finish(), finish has different meanings other than stop. A user-intended finish is very useful for simulation control.

https://github.com/freechipsproject/chisel3/blob/473a13877c60ba9fb13de47542a8397412c2b967/core/src/main/scala/chisel3/Assert.scala#L80-L92

chick commented 4 years ago

I think this is how stop works. Stop has a return code. Zero is considered success any other value is considered a failure diagnostic code. I think the problem is that the stop result is not exposed by the unit test frameworks. That should not be hard to fix if that is the problem

davidmlw commented 4 years ago

What is the current verilog emission result? I just have a look. It seems stop is translated to "$fatal" and returns no code. Maybe it needs a Chisel3, Firrtl, Treadle synergy to have a standard spec for stop and finish.

davidmlw commented 4 years ago

According to https://www.eg.bucknell.edu/~csci320/2016-fall/wp-content/uploads/2015/08/verilog-std-1364-2005.pdf, Page 302. Verilog $finish is not used to return status code to system. Acctually Verilog (2005) standard has no primitives to return a code outside.

In SystemVerilog (2017), http://ecee.colorado.edu/~mathys/ecen2350/IntelSoftware/pdf/IEEE_Std1800-2017_8299595.pdf Page 606, it provide $fatal. While the return code of $fatal is limited to 0, 1, 2 as same as $finish.

It is very interesting that (System)Verilog had chosen not to provide a code-returning scheme.

So this recommendation need further considerations:

  1. Whether Chisel3, Firrtl, Treadle implement the Verilog standard stop and finish. I would propose yes.
  2. Whether Chisel3, Firrtl, Treadle implement a new primitive that control the simulation and return a status code outside. I would propose yes. exit (Int): Unit and exit (UInt): Unit can be used.
  3. Provide a equivalent scheme for Verilog, at least for Verilator.
sequencer commented 4 years ago

Maybe the ultimate way to this is trying to add DPI calling to chisel?