Add place and route script

[jthornblad]

Description

Run multiple threads of nextpnr-ice40 to find a seed that gives a layout that meets timing.

Type of change

Please tick any that are relevant to this PR and remove any that aren't.

• Bugfix (non breaking change which resolve an issue)
• Feature (non breaking change which adds functionality)
• Breaking Change (a change which would cause existing functionality to not work as expected)
• Documentation (a change to documentation)

Submission checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my changes
• I have tested and verified my changes on target
• My changes are well written and CI is passing
• I have squashed my work to relevant commits and rebased on main for linear history
• I have added a "Co-authored-by: x" if several people contributed, either pair programming or by squashing commits from different authors.
• I have updated the documentation where relevant (readme, dev.tillitis.se etc.)
• QEMU is updated to reflect changes

[dehanj]

Nice work, have not tested it yet - but maybe this should be in the tools folder? hw/application_fpga/tools is where we have other scripts or tools that we use

[jthornblad]

Done

[dehanj]

I think this is good enough.

Some minor comments but not blocking in my opinion:

• It says "Set target frequency for design in MHz (might be overridden from value in synthesis file)". I wonder when this is not overridden? When I test it does not matter, it always get overridden by the synth.json. Should the comment say that it should be the same as was used when the synth.json was built?

[dehanj]

Can also verify that I managed to run the script, get a valid seed to achieve 24 Mhz, then put it in the Makefile and it still gives the same result.

The seed that worked for me 4086954404853248473, it gave 24.19 MHz.