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<gundy>
Is this a reasonable place to ask questions about nextpnr?
<ZipCPU>
About as good as any
<ZipCPU>
Some of the developers are on this channel
<gundy>
actually, don't worry - I think I know what's going on... I've just switched from arachne-pnr to nextpnr, and started seeing some "Floating wire node value, [X] on [Y], converted to zero driver" warnings around some of the BRAM blocks I was using.
<gundy>
I _think_ that it might just be warning me that it's assembled/synthesised things in such a way that not all of the ports on the underlying blocks are used.
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<daveshah>
Just ignore those warnings
<daveshah>
They shouldn't be printed in that case
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<gundy>
cool, thanks.. actually, since you're here, big thanks for all the work you've put into the OS toolchain!!
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<ZipCPU>
daveshah: That's a shout out to you :D
<daveshah>
Cheers gundy!
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<ZipCPU>
Yaaayyy!! I just managed to formally verify my first RISC-V core using riscv-formal! (It's a client's core, and not my own--this is just my first time using riscv-formal)
<ZipCPU>
It's a series of tests that a RISC-V CPU should pass in order to be called a RISC-V CPU
<ZipCPU>
This was my first project using it
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<sammy>
I'm guessing I can't use it to verify a RISCV CPU written in VHDL?
<ZipCPU>
You could ...
<ZipCPU>
But you'd need to get the commercial copy of Yosys to do it with
<ZipCPU>
Likewise for a SystemVerilog version
<sammy>
I thought the idea with formal is to have the assertions embedded with the HDL. Does this insert assertions?
<ZipCPU>
Not necessarily
<ZipCPU>
That's actually a statement of debate
<ZipCPU>
The industry standard is to place the formal assertions *outside* of the HDL
<ZipCPU>
I do the opposite, placing my assertions in the same HDL file, but after the HDL
<ZipCPU>
Part of the reason for doing this is that Yosys (the only FV solution I could afford) doesn't support referencing variables from within submodules other than through a module port
<ZipCPU>
Hence if you have a design, toplevel, with a CPU within it, cpu, and a decoder within that, at the toplevel you might wish to support the instruction within the decoder as toplevel.cpu.decoder.instruction
<ZipCPU>
The free version of yosys doesn't support this notation
<ZipCPU>
Hence, I'm confined to placing assertions within the HDL in question
<ZipCPU>
riscv-formal handles this by passing a packet of instruction information through the CPU's toplevel port list
<ZipCPU>
The riscv-formal tests are then applied to this packet of information