MUXF8 vivado compatibility

[mcmasterg]

A number of fuzzers (and associated minitests) work on Vivado 2017.2 but are broken on Vivado 2017.3. A quick analysis shows its related to MUXF8.

[mcmasterg]

Added some additional info to a minitest: #19

[mcmasterg]

The fundamental issue is likely that I'm abusing LUT6_2 in a way that worked in Vivado 2017.2 but not later. MUXF7 and MUXF8 are intended to be used to create very large LUTs by combining multiple LUT6s. Theoretically you could use this to create LUT6 or LUT7 from a LUT5 of a LUT6_2, but its of questionable merit and likely untested.
So the fuzzers should be rewritten to switch between LUT6 and LUT6_2 as needed instead of using LUT6_2 exclusively. The current strategy was chosen as it nearly fully populates the CLB and only tweaks things were needed. So if this is changed it may lead to some aliasing, but this should be solvable.

[JohnDMcMaster]

More recent Vivado versions have more severe issues like renaming ports on LUT6_2. Given this and other minor changes that will cause a lot of maintenance issues without a huge impact on the success of this project, I'm going to declare this "won't fix" until we have a more specific reason to fix this.

[mithro]

@JohnDMcMaster We should have a more generic issue about making the fuzzers work with newer versions of Vivado?

[mcmasterg]

I'm saying that I don't think its worth the effort. The return on investment is not good

[mithro]

Depends on if we want to support devices only in newer releases.

[mithro]

Just if anyone looks at this in the future. It also looks like the newest Vivado (2018.02) doesn't like some of the things we are doing with LUTs.

ERROR: [Opt 31-67] Problem: A LUT6 cell in the design is missing a connection on input pin I0, which is used by the LUT equation. This pin has either been left unconnected in the design or the connection was removed due to the trimming of unused logic. The LUT cell name is: roi/dos[0].lut.
Resolution: Please review the preceding OPT INFO messages that detail what has been trimmed in the design to determine if the removal of unused logic is causing this error. If opt_design is being specified directly, it will need to be rerun with opt_design -verbose to generate detailed INFO messages about trimming.

[JohnDMcMaster]

Right. Before it was a recommendation now it's a requirement. We should fail maybe during settings.sh if a non complaint version is tried

…

On Fri, Jan 4, 2019, 9:21 AM Tim Ansell ***@***.*** wrote: Just if anyone looks at this in the future. It also looks like the newest Vivado (2018.02) doesn't like some of the things we are doing with LUTs. ERROR: [Opt 31-67] Problem: A LUT6 cell in the design is missing a connection on input pin I0, which is used by the LUT equation. This pin has either been left unconnected in the design or the connection was removed due to the trimming of unused logic. The LUT cell name is: roi/dos[0].lut. Resolution: Please review the preceding OPT INFO messages that detail what has been trimmed in the design to determine if the removal of unused logic is causing this error. If opt_design is being specified directly, it will need to be rerun with opt_design -verbose to generate detailed INFO messages about trimming. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#14 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AANj21bpiMQlOhH1wOW0LPwnbJjORgV1ks5u_w8JgaJpZM4RLVMT> .

[kammoh]

Vivado 2017.2 is no longer even available for download. Could you please reconsider planning a fix for this issue? Especially with @daveshah1 's nextpnr-xilinx dependence on prjxray (which probably should not even be affected by the MUXF8 compatibility?)

[mithro]

@kammoh 2017.2 is available in the archive @ https://www.xilinx.com/support/download/index.html/content/xilinx/en/downloadNav/vivado-design-tools/archive.html

Vivado HLx 2017.2: WebPACK and Editions - Windows Self Extracting Web Installer
Vivado HLx 2017.2: WebPACK and Editions - Windows Self Extracting Web Installer
(EXE - 51.59 MB)

MD5 SUM Value : c0f1f42b33a39957d85b0d4548717f80

Vivado HLx 2017.2: WebPACK and Editions - Linux Self Extracting Web Installer (BIN - 85.24 MB)

MD5 SUM Value : eaee62b9dd33d97955dd77694ed1ba20

Vivado HLx 2017.2: All OS installer Single-File Download (TAR/GZIP - 22.13 GB)

MD5 SUM Value : 958f190a089ad3f39d327d972c7dcf35

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We would welcome someone fixing the problem but it isn't a high priority for the current contributors.

Downloads

Vivado - Embedded Development - SDx Development Environments - ISE - Device Models - CAE Vendor Libraries

[mithro]

Also, there is pre-built output from this repo at https://github.com/SymbiFlow/prjxray-db

GitHub

SymbiFlow/prjxray-db

Project X-Ray Database: XC7 Series. Contribute to SymbiFlow/prjxray-db development by creating an account on GitHub.

[nalzok]

Just curious, can we delete the following instructions on the quick start page now? It appears to me that this issue has been addressed.

Why 2017.2? Currently the fuzzers only work on 2017.2, see Issue #14 on prjxray.

Is 2017.2 really required? Yes, only 2017.2 works. Until Issue #14 is solved, only 2017.2 works and will be supported.