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Comment by krupan | Hacker News Reader

For complex designs the simulator that comes with the Vivado tools (Mentor's modelsim) is not going to cut it. I wonder if they are working on deals with Mentor (or competitors Cadence and Synopsys) to license their full-featured simulators.

Even better, maybe Amazon (and others getting into this space like Intel and Microsoft) will put their weight behind an open source VHDL/Verilog simulator. A few exist but they are pretty slow and way behind the curve in language support. Heck, maybe they can drive adoption of one of the up-and-coming HDL's like chisel, or create one even better. A guy can dream...

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Nowadays, I don't believe you need a paid-for simulator like Questa, VCS, etc. I am developing verilog in my day job for FPGA's using icarus verilog (an open source simulator)which works fine for fairly large real world designs (I am also using cocotb for testing my code) and supports quite a lot of system verilog too.

As someone who has little experience with FPGAs beyond some experiments with a Spartan-6 dev board that mostly involved learning to write VHDL and building a minimal CPU, I found the simulator to be of limited use. My tiny projects were small enough that the education simulator was plenty fast. It was nice when I didn't have the board available, and occasionally, the logic analyzer was useful when I didn't understand what my code was doing to a data structure. But usually, it was just a lot easier to simply flash the board and run the thing.

What's the use of a simulator when you can spin up an AWS instance and run your program on a real FPGA?

Simulations give you better controllability and better visibility. In other words, you can poke and prod every internal piece of the design in simulation land. In real hardware, not so easy.

That being said, you are far from alone as an FPGA developer in skipping sim and going straight to hardware. Tools like Xilinx's chipscope help with the visibility problem in real hardware too.

> For complex designs the simulator that comes with the Vivado tools (Mentor's modelsim) is not going to cut it.

It's now called QuestaSim I believe. But are you sure it can't handle simulating large designs? If yes, what is the full-featured software from Mentor that can?

> Heck, maybe they can drive adoption of one of the up-and-coming HDL's like chisel

Chisel isn't a full-blown HDL from what I understand; it's only a DSL that compiles to Verilog. In other words, you'd still need a Verilog simulator to actually run your design.

Questa is the full blown tool. Modelsim is a step down and that's what comes with FPGA tools. Usually the version of modelsim that Xilinx and Altera ship is crippled performance wise.

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