clifford changed the topic of #yosys to: Yosys Open SYnthesis Suite: http://www.clifford.at/yosys/ -- Channel Logs: https://irclog.whitequark.org/yosys
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<promach3> For http://sci-hub.tw/https://ieeexplore.ieee.org/document/4751932 , why the cyclic combinational path of wavefront arbiter could not be handled by EDA tool ?
<tpb> Title: Sci-Hub: устраняя преграды на пути распространения знаний (at sci-hub.tw)
<whitequark> EDA tools like Yosys and nextpnr focus on synchronous logic
<promach3> whitequark: are you familiar with structure of wavefront arbiter ?
<whitequark> I am not
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<tpb> Title: Wavefront arbiter - Wikipedia (at en.wikipedia.org)
<whitequark> I don't understand how it works, but cyclic combinatorial paths are essentially equivalent to asynchronous logic
<whitequark> a lot of existing tooling chooses not to bother with anything more complex than a latch (often latches too)
<whitequark> there are a few issues here. first, LUTs usually aren't glitchless, so techmapping combinatorial cycles correctly is hard
<whitequark> second, you have to somehow determine the worst case time for it settling to a fixpoint to provide timing analysis
<promach3> ok
<promach3> whitequark: maybe https://images.slideplayer.com/29/9485249/slides/slide_8.jpg helps in understanding
<whitequark> sure
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<lukego> whitequark: much obliged for the docs update :) I'll try to be such a good citizen too.
<lukego> emily: cool :)
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<daveshah> lukego: twitter thread for you haha
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<hackerfoo> Does Yosys perform any numerical analysis e.g. optimize out any bits higher than the low N+1 of the result of adding two N bit inputs?
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<mwk> yes
<mwk> and that particular case is definitely handled
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<daveshah> Several more complex cases aren't though
<daveshah> eg a+b-b may well not be optimised away
<mwk> (it's not)
<daveshah> I think abc9 will usually work it out as it can see through the carry chains, in practice
<daveshah> Old abc won't if it is mapped to carries though
<mwk> hmm
<mwk> it doesn't optimize even for plain "synth" to gates
<daveshah> synth uses some weird abc script that disables a lot of optimisations
<daveshah> I think if you do a normal "abc" after synth it optimises
<mwk> oh, yeah
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