Lucas Sifoni

35c3 Leipzig notes - Symbiflow : GCC for FPGAs ?


I had the pleasure to go to the 35th edition of the Chaos Communication Congress. Here are some notes of some talks.

Symbiflow : the GCC of FPGAs

Tomu : a FPGA inside an USB port. Still missing a bootloader. iCE1040

Symbiflow : 8 people work on it in some way or another. Replacing the (plural) proprietary toolchain with open tools when it comes to programming FPGAs.

Compiler -> frontend (generic optimizations) -> specific backend

EDA : VHDL | VERILOG -> Synthesis tools -> ASIC tools | FPGA tools | Simulation tools

Symbiflow is currently a toolchain from Verilog to FPGA bitfiles. GCC metaphor in the sense of FLOSS + XPlatform + Pluggable.

Project IceStorm : Synthesis + FPGA Tools Yosis arachne-pnr + Project IceStorm.

Project X-Ray

Last year, symbiflow was meant to target two distinct FPGA architectures and document the process of getting there.

Training and demonstration on project 2064 (xlilinx xc20xx) : solving the symbiflow process for this 20-old-chip should serve as a guide to have a rigorous process for every type of later FPGA. The Symbiflow project aims to build a generic frontend AND backend for every existing FPGA. Contribution is welcome for any chip.

At the time, the project is conducted as a means of experimentation on the documentation process. That’s pretty clever and humble.

Synthesis, mapping, P&R : The bistream being documented is only a third of the project : tooling must be developed. That’s where Yosys and nextpnr (or Verilog To Routing) come into play. Both tools plug into Yosis which serves as a frontend.

NextPNR & VTR are timing-driven.

Update tutorials about arachne-pnr for NextPNR ? Lattice ICE40 is a nice chip to start.

See TOMU for USB-insider ARM processors

Calls for help even with simple tasks

How did you reverse engineer bitstreams ? We couldn’t, legal prevented us to do so. We (simplified) randomized loaded bitstreams and observed across runs which bits were set when a particular feature was on.

Why is there no VHDL support ? Too complicated, clunky.

What about CPLD support ?

Why the split between NextPNR & VTR ? VTR = academic research tool, but slightly worse bitgen NPR = nice gui, better bitgen

Are vendors hostile or ready to collaborate on this project ? A : some are hostile, some start to be ready to consider OSS tooling. AAt the end of the day, this is sales-driven.

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