whitequark changed the topic of #yosys to: Yosys Open SYnthesis Suite: https://github.com/YosysHQ/yosys/ | Channel logs: https://libera.irclog.whitequark.org/yosys/ | Bridged to #yosys:matrix.org
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<famubu[m]> :q
<famubu[m]> While doing p&r with nextpnr, it prints two slack histograms. What is the unit used there? Is it nano-second or pico-second?
<famubu[m]> Also, what changes are done between the first and second histogram?
<famubu[m]> My first random thought was that the first histogram is after placing but before routing. But slack can only be calculuated after routing, right? Or am I wrong there?
<famubu[m]> I got an example histogram like this (a 6-bit ring counter): https://bpa.st/HEGA
<tpb> Title: View paste HEGA (at bpa.st)
<tnt> First one is estimates post-place, pre-routing. Second is post routing.
<tnt> units are ps
<famubu[m]> Okay, so slack calculation can be done before routing itself.
<famubu[m]> Where does it get the route/link/path data before routing? From the netlist output by yosys itself?
<famubu[m]> I suppose routing process finds more optimal routes.
<famubu[m]> Also in the histogram I pasted, it says 'Max delay posedge clk_IBUF_I_O -> <async>: 6.69 ns'
<famubu[m]> From that I first figured the histogram slack times would be in ns. But then I saw it in ps here: https://github.com/YosysHQ/nextpnr/pull/31
<famubu[m]> Is the max delay mentioned here have any relation to slack times in the histogram?
<tnt> They're just guess estimates based on the length AFAIK.
<famubu[m]> The maximum slack in the histogram was 36181ps, which is 36.181ns. Which is way more than the 6.69ns. So I was wondering.
<famubu[m]> nextpnr also prints this table: https://bpa.st/GDZQ
<tpb> Title: View paste GDZQ (at bpa.st)
<famubu[m]> What information does it convey? Internet search said ripup is a routing algorithm.
<famubu[m]> Does w/ripup=200, wo/ripup=226 mean that routing was able to make savings?
<tnt> That's just a progress status for routing ... yours is so simple it only prints progress once but for complex routing you can see the evolution of how much is left to route and elapsed time and such.
<famubu[m]> Oh..
<famubu[m]> Thanks!
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