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Question about constraints #126
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We are moving to XDC, but some of the old demos were written when only PCF support existed. |
Ok, great. What about to specify in |
I think that is just a mistake? |
@rodrigomelo9 It actually is expected it to be like that.
Additionally, XDC and PCF should not be used at the same time and it is better to use XDC, given that they can contain also timing and other constraints. |
@acomodi -- This seems incorrect. The XDC should contain the IO placements (as well as other constraints)? Is the problem that we are missing a tool which generates the IO constraints file for VPR from an XDC input? |
@mithro This is what is happening, the XDC contains all kinds of constraints including the placement ones. The yosys plugin can read the placement constraints and save them in the eblif, for the io place constraints script to generate the VPR constraint files |
@acomodi -- So the PCF file is being generated by the output of Yosys which is then converted into the correct format needed by VPR? |
@mithro No. There are two independent flows concerning IO placement constraints, depending on what the user chooses: |
I think we might have discussed this previously. We should hand in the PCF at the same place we hand in the XDC and then the rest of the flow should be the same. See chipsalliance/yosys-f4pga-plugins#30 and maybe https://docs.google.com/drawings/d/1r2LXypJF5AD40LfHegml3_fIvPT2jZ3n2OZYW9-9dLU/edit ?
|
Thanks. My question was answered, so this issue can be closed if you want (I mean, it seems that @mithro detected another problem, but that is not what this issue was about). Regards |
Hi. It seems that both,
pcf
andxdc
are supported.I was comparing the three xc7 examples. Taking for example
arty
, I found:counter_test/arty.xdc
linux_litex_demo
:arty.pcf
arty.xcf
picosoc_demo/arty.pcf
Comparing the
Makefiles
:symbiflow_synth
,counter_test
andlinux_litex_demo
specify-x ${XDC}
(don't used bypicosoc_demo
)symbiflow_place
,linux_litex_demo
andpicosoc_demo
specify-p ${PCF}
(don't used bycounter_test
)Is the same to use
-x ${XDC}
forsymbiflow_synth
and-p ${PCF}
forsymbiflow_place
? Do I need to choose only one option? Has it sense to support the two alternatives? Recommendation? In my opinion, in place has more sense (but is using pcf instead of xdc). Is it taken into account for synthesis?).Clarification will be welcome.
Regards,
Rodrigo
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