Do we use the proper Yosys libraries?

[zapta]

This came out from another discussion here. We work with three architectures ICE40, ECP5, and GOWIN and perform lint and sim operations on Yosys projects. The table below shows the oss-cad-suite libraries we use and the ones for ECP5 seem to be off. Do we use the proper libraries?

	Lint (Verilator)	Sim (Iverilog)
ICE40	share/yosys/ice40/cells_sim.v	share/yosys/ice40/cells_sim.v
ECP5	share/yosys/ecp5/cells_bb.v	share/yosys/ecp5/cells_bb.v
GOWIN	share/yosys/gowin/cells_sim.v	share/yosys/gowin/cells_sim.v

[KrystalDelusion]

As I understand it the cells_bb files are autogenerated and cells_sim are not (or much less so at any rate). cells_bb only have blackbox definitions, while cells_sim can include both simulation models and blackbox definitions. At a glance they appear to be non-overlapping, so if both files exist you should use both.

[zapta]

Thanks @KrystalDelusion. Below is the list of files from the latest oss-cad-suite build that have 'ecp5' and 'cell' in their path. Which ones should we use for lint and which one for sim?

Also, is there a way to find out what library files yosys and nextpnr use during a build?

$ find . | grep ecp5 | grep cell
./share/yosys/lattice/cells_sim_ecp5.v
./share/yosys/lattice/cells_bb_ecp5.v
./share/yosys/ecp5/cells_ff.vh
./share/yosys/ecp5/cells_sim.v
./share/yosys/ecp5/cells_io.vh
./share/yosys/ecp5/cells_bb.v

[KrystalDelusion]

I'm not sure about nextpnr (though I think it has its own definitions), but for Yosys you can call (e.g.) yosys -h synth_ice40 (or help synth_ice40 from a Yosys shell) and you can see the list of commands it calls. When a file starts with a + as in +/ice40/cells_sim.v it refers to the share directory. For some synth flows, such as synth_lattice you may notice that the files referenced don't actually exist as given, so you may need to run the flow after calling echo on which will print the command exactly as called to the log (for synth_lattice the help text lists e.g. +/lattice/cells_sim.v, but the actual file depends on the family used and will instead resolve to e.g. +/lattice/cells_sim_ecp5.v).

synth_ecp5 and the share/yosys/ecp5 directory are maintained for backwards compatibility but are otherwise just references to synth_lattice and copies of share/yosys/lattice files respectively:

$(eval $(call add_share_file,share/ecp5,techlibs/lattice/cells_ff.vh))
$(eval $(call add_share_file,share/ecp5,techlibs/lattice/cells_io.vh))
$(eval $(call add_share_file,share/ecp5,techlibs/lattice/common_sim.vh))
$(eval $(call add_share_file,share/ecp5,techlibs/lattice/ccu2c_sim.vh))
$(eval $(call add_share_file_and_rename,share/ecp5,techlibs/lattice/cells_sim_ecp5.v,cells_sim.v))
$(eval $(call add_share_file_and_rename,share/ecp5,techlibs/lattice/cells_bb_ecp5.v,cells_bb.v))

If you check lattice/cells_sim_ecp5.v (or ecp5/cells_sim.v) you can see that the file includes all four of the .vh files (including the two your search identified). As already mentioned, the only way to get all hardware module definitions (and available sim models) is to load both cells_sim and cells_bb. For ECP5 you can use either the ecp5/cells_*.v files, or lattice/cells_*_ecp5.v (again, the contents of both are the same, the lattice directory is just the newer path that merges all of the lattice family to simplify maintenance). As far as I know we do not have or distribute simulation models for all of the ECP5 cell types, but those we do distribute are loaded by cells_sim_ecp5.v.

If you are using linting to detect unsupported blackboxes I think you need both cells_sim.v and cells_bb.v. For simulation you may be able to ignore the cells_bb.v file.

Note that in Yosys you can use the hierarchy command with -check to check no unknown modules (e.g. unsupported blackboxes) are instantiated or -simcheck to also check that no blackboxes are instantiated.

[zapta]

Thanks @KrystalDelusion, this is very useful, I will take time to digest and understand it.