Comment by variadix | Hacker News Reader

Comment by variadix | Hacker News Reader

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I’m not exactly sure what you’re getting at, but I think I’ve had a similar question: why don’t HDLs have language elements more representative of what digital circuits are constructed from, namely synchronous and asynchronous circuits, rather than imperative input triggered blocks (processes IIRC, it’s been a while)?

I always thought it was confusing to design a circuit mentally (or on paper) out of things like muxes, encoders, flip flops, etc. and not have language-level elements to represent these things (without defining your own components obviously).

I remember looking this up, and I believe it’s because the languages were originally designed for simulation and verification, and there are things you might want to do in a simulation/verification language for testing that are outside of what the hardware can do. Mixing the two is confusing IMO, but clearly demarcating the hardware-realizable subset of the language would be better than the current state.

Because it's both slow and terrible?

You generally do not want to simulate or describe raw gate-level netlists. Both languages are capable of that. Old school Verilog (not SystemVerilog) is still the defacto netlist exchange format for many tools.

It's just aggravatingly slow to sim and needlessly verbose. Feeding high-level RTL to Verilator to do basic cycle-accurate sim has exceptionally fast iteration speed these days.

Is it really if you restrict yourself to sensible design practices? You generally want to simulate simple clocked Logic with a predefined clock, most of the time anything else is a mistake or bad design. So just if rising edge clk next_state <= fn(previous_state, input) . It seems to me VHDL and verilog are simply at the wrong abstraction level and by that they make simulation needlessly complicated and design easy to do wrong. To me it seems that if they had the concept of clocks instead none of this would be necessary and many bugs avoided (but I'm no expert on simulator design, so I might be missing something...)

I agree basically with everything you're saying, but that's not arguing for raw gate netlists. If anything it's arguing for even higher levels of abstraction where clock domains are implicit semantic contexts.

Many new school HDLs are working in this space and they couldn't be farther from the "representative of what digital circuits are constructed from" idea. Often they're high-level programmatic generators, very far from describing things in terms of actual PDK primitives.

In a way is further away, but in another way it's actually closer to how real hardware works: Clock (and reset) trees are real physical things which exist on all digital chips.

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