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0 pointsdaxfohl5y ago0 comments

Agreed. I never thought the mental leap to Verilog was a big hurdle. It's just C-like syntax with some new constructs around signaling and parallelism. I found this interesting rather than foreboding.

The main challenge I had was compilation time. It can sometimes take overnight to compile a simple application if there's a lot of nested looping, only to have it run out of gates. This can be a royal pain.

I'd expect most HPC scenarios would have lots of nested looping, and probably memory accesses, and thus have to spend a lot of time writing state machines to get around gate count limitations and wait for memory responses, at which point you're basically designing a 200 MHz CPU.

So I don't see it as being very useful for general purpose acceleration, but could be a good CPU offload for some very specific use cases that are more bit-banging than computing. Azure accelerates all its networking via FPGA, which seems like the ideal use case.

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CamperBob25y ago

There's no such thing as a "loop" on an FPGA. If you declare a loop in Verilog, the synthesizer allocates one set of gates per iteration. That's probably why your runs take all night.

HLS notwithstanding, you don't use traditional control structures to tell an FPGA what to do. You use clocked FSMs and asynchronous expressions to tell it what to be.

daxfohlOP5y ago

Right. But for HPC, loops (in Verilog) will be the norm, to squeeze out as much from each clock tick as possible. Running everything as discrete steps in a FSM would defeat the purpose.

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