[Libre-soc-dev] LibreSOC Implementation on arty7 fpga dev boards.

lkcl luke.leighton at gmail.com
Sat Oct 9 14:24:42 BST 2021

On October 9, 2021 8:50:37 AM UTC, varun mohan <varunmadhavam at gmail.com> wrote:
>I finally got it to synthesize this time.


>The issue was (and I think i missed to convey this point) that i had
>installed symbiflow using conda.


>It comes with its own version of yosys...!!!.

ahh yes, that would do it.

>make: Leaving directory
>symbiflow_synth -t arty -v
>/opt/src/litex/libresoc-litex/build/arty/gateware/arty.v -d artix7 -p
>xc7a35tcsg324-1 -x arty.xdc > /dev/null
>symbiflow_pack -e arty.eblif -d xc7a50t_test -s arty.sdc > /dev/null
>symbiflow_place -e arty.eblif -d xc7a50t_test -p arty.pcf -n arty.net
>xc7a35tcsg324-1 -s arty.sdc > /dev/null
>Warning: IDELAY_GROUPS parameters are currently being ignored!
>/opt/tools/symbiflow/xc7/install/bin/vpr_common: line 94: 93453
>Segmentation fault      (core dumped)

that's impressive! :)

this is a fault with the vpr router program that is beyond our control.

more specifically: it is a fault with the *optimised* version of vpr that was patched (i think) by... advansys? advantec?  someone was contracted (i think) by google to speed up vpr to make it multi-threaded, which means it's possible that the fault was caused by the optimisation modifications: it's too early to tell, one way or the other.

the segfault should be reported on the irc.libera.chat #symbiflow channel because they will want the coredump and other details in order to be able to investigate.

because it is *not* the standard upstream version of vpr, you should *not* immediately contact the upstream vpr developers... not yet.  but, we need to work that out.

now.  if your first instinct is to "throw away everything and start again, but replace vpr", this again risks not having the exact same conditions.

what i recommend you do (to save a lot of time) is:

0) take a backup snapshot of the chroot so that you
     have everything needed to provide to #symbiflow
1) take a SECOND copy of the schroot and duplicate
     it under a new chroot name
2) manually create the /etc/schroot files needed
     (copy those too, look in *all* subdirectories
       you will find an fstab and others, check what
       mk-deb-chroot does at the start and follow it)
3) *deinstall* the (optimised) version of vpr *only*
     from the copy of the chroot.
     do NOT alter ANY other files or programs.
4) *manually* install the *upstream* version of
     vpr and you will find instructions that Veera has
     done on how to do that, at:
5) join #libre-soc IRC because you will find that
     Veera is on there and it will be easier to talk
     to him about how he set up symbiflow and the
     installation of vpr.

if and *only* if the exact same segfault occurs once you have used the *upstream* version of vpr should you contact the upstream developers and let them know.

we, Libre-SOC, obviously cannot fix this show-stopping bug in vpr because we are all users of vpr just like you are.  you can however with the right information help them to reproduce the error so that they can fix it.  unfortunately there is no guarantee of action being taken but generally software libre developers like to be informed of bugs because their reputation is important to them.

hopefully if you use the (slower, upstream) version of vpr, you might get lucky and it completes routing.  if so that's great.

welcome to being on the bleeding edge of software development :)


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