[gothenburg]

"Another property is that there is no synthesizable subset in Cx. As far as I know, this is very rare in languages for hardware design, but the language is entirely synthesizable. You never have to think about synthesis versus simulation. Exactly like in software, nobody ever wonders if they can write code that won't run on the processor :-)"

This is scary. I want the tool to tell me "I can't synthesize this" because when it does, it might infer characteristics of the design that I might not want.

Do you have some kind of paper or detailed explanation about this part?

Sometimes a bad design is not bad because it's badly written, it's bad because it's not complying with some timing constraints or because the synthesis tool decided to infer some crazy system from the code the designer wrote.

[MootWoop]

@gothenburg @mng2 I get that you think it's not useful or even it's crazy, especially as both of you seem to be seasoned hardware designers. But as a software guy myself, there's nothing I have found more horrible when learning to write some VHDL than finding out what was allowed in synthesis, what was tolerated but not recommended, and what was legal VHDL but could never synthesize. Things like automatically inferred latches because of local variables, multidimensional arrays supported but not always (vendor-dependent), loops that work for combinatorial logic only, "wait" that are not permitted (or only in vendor-specific ways), etc.

In Cx you can't create latches, loops work for combinatorial logic and synchronous logic alike, and all in all there are no unsynthesizable constructs. Finding out if a piece of code will result in unacceptable performance is a different problem, I hope to have the compiler kind of "guide" you on this kind of things.

[scott_s]

Is it any scarier than having wildly inefficient software code? (Think a naive traversal of large matrices that thrashes the cache.)

That's a workflow where optimization requires knowing the internals and how they interact, but you can ignore such things if you just want correctness. At least in software, that model works well, because the performance of most of the code we write doesn't matter - even in applications where performance is a concern.

[mng2]

I wouldn't call it 'scary', myself, but it doesn't strike me as a particularly useful feature. In software, a single slow subroutine can simply take up more cycles. But in hardware, a slow path becomes your critical path, and you have a hard clock cycle requirement. (Sure, you can use multi-cycle paths and/or change clock speed, but those generally have to be adjusted manually/physically, and not all design situations will have that flexibility.)