This commit tries to carefully follow the documented behavior of LSE
and Synplify. It will use `syn_ramstyle` attribute if there are any
write ports, and `syn_romstyle` attribute otherwise.
* LSE supports both `syn_ramstyle` and `syn_romstyle`.
* Synplify only supports `syn_ramstyle`, with same values as LSE.
* Synplify also supports `syn_rw_conflict_logic`, which is not
documented as supported for LSE.
Limitations of the Yosys implementation:
* LSE/Synplify support `syn_ramstyle="block_ram,no_rw_check"`
syntax to turn off insertion of transparency logic. There is
currently no way to support multiple valued attributes in
memory_bram. It is also not clear if that is a good idea, since
it can cause sim/synth mismatches.
* LSE/Synplify/1364.1 support block ROM inference from full case
statements. Yosys does not currently perform this transformation.
* LSE/Synplify propagate `syn_ramstyle`/`syn_romstyle` attributes
from the module to the inner memories. There is currently no way
to do this in Yosys (attrmvcp only works on cells and wires).
This commit:
* renames all remaining instances of "DRAM" (which is ambiguous)
to "LUTRAM" (which is not), finishing the work started in
the commit 698ab9be;
* renames memory rule files to brams.txt/lutrams.txt;
* adds/renames script labels map_bram/map_lutram;
* extracts where necessary script labels map_ffram and map_gates;
* adds where necessary options -nobram/-nolutram.
The end result is that BRAM/LUTRAM/FFRAM aspects of every target
are now consistent with each other.
Per architecture:
* anlogic: rename drams.txt→lutrams.txt, add -nolutram, add
:map_lutram, :map_ffram, :map_gates
* ecp5: rename bram.txt→brams.txt, lutram.txt→lutrams.txt
* efinix: rename bram.txt→brams.txt, add -nobram, add :map_ffram,
:map_gates
* gowin: rename bram.txt→brams.txt, dram.txt→lutrams.txt,
rename -nodram→-nolutram (-nodram still recognized), rename
:bram→:map_bram, :dram→:map_lutram, add :map_ffram, :map_gates
whitequark