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> These tools take C or C++ code and produce a transistor layout to be used by the FPGA. Hmm, I haven’t been following that but it seems that... > The result

> These tools take C or C++ code and produce a transistor layout to be used by the FPGA. Hmm, I haven’t been following that but it seems that... > The result is massively larger FPGA/HLS programs than the programmer needed And there it is. Really seems odd to me to try and force procedural C into non-linear execution of FPGA. Like it seems super odd, and when talking about changes to C to help that... I really don’t get it. This isn’t what C is for. What is the performance advantage over Verilog? How many people want n-bit into in C when automatically handled structures work well for most people. Maybe I’m just not seeing the bigger picture here and that example was just poor?

Cyph0n 6y ago
Not to mention that the first statement is simply false... The final result is a bitstream that determines which LUTs (lookup tables) and BRAM (memory/block RAM) to use on the chip, and how they should be connected/routed. The FPGA fabric itself is made of transistors, but your C/C++ (HLS) or HDL code is not directly controlling these transistors. This is what makes FPGAs so flexible relative to ASICs.
marcan_42 6y ago
There is no performance advantage over Verilog. The reason why (some) people want C is because Verilog and VHDL are unquestionably terrible languages (they weren't even intended to be HDLs, that use case came later) which are damn near impossible to write complex systems in without spending most of your time writing bug-prone boilerplate. Every big name IC designer shop ends up wrapping them in layers of metaprogramming to make them palatable. So, since those languages suck, people familiar with the procedural side of things end up asking for C. Which is an even bigger impedance mismatch than Verilog, but since you need a smarter backend to even begin to implement it, it can make life easier by that alone. Personally, I prefer stuff like nMigen, which is basically Python metaprogramming a synthesis-oriented subset of Verilog constructs. Compiles down to Verilog behind the scenes.
- krupan 6y ago
  "Verilog and VHDL are unquestionably terrible languages (they weren't even intended to be HDLs, that use case came later)" They were intended to be HDLs (for simulation of hardware), but they were never intended to be automatically translated into gates/schematics (i.e., synthesized)

Cyph0n 6y ago

Not to mention that the first statement is simply false... The final result is a bitstream that determines which LUTs (lookup tables) and BRAM (memory/block RAM) to use on the chip, and how they should be connected/routed. The FPGA fabric itself is made of transistors, but your C/C++ (HLS) or HDL code is not directly controlling these transistors. This is what makes FPGAs so flexible relative to ASICs.

marcan_42 6y ago

There is no performance advantage over Verilog. The reason why (some) people want C is because Verilog and VHDL are unquestionably terrible languages (they weren't even intended to be HDLs, that use case came later) which are damn near impossible to write complex systems in without spending most of your time writing bug-prone boilerplate. Every big name IC designer shop ends up wrapping them in layers of metaprogramming to make them palatable. So, since those languages suck, people familiar with the procedural side of things end up asking for C. Which is an even bigger impedance mismatch than Verilog, but since you need a smarter backend to even begin to implement it, it can make life easier by that alone. Personally, I prefer stuff like nMigen, which is basically Python metaprogramming a synthesis-oriented subset of Verilog constructs. Compiles down to Verilog behind the scenes.

krupan 6y ago
"Verilog and VHDL are unquestionably terrible languages (they weren't even intended to be HDLs, that use case came later)" They were intended to be HDLs (for simulation of hardware), but they were never intended to be automatically translated into gates/schematics (i.e., synthesized)