Preventing the use of specific library cells in the entire flow

[ishwars1618]

Hello,

I am trying to avoid the use of specific library cells (whose prefix I know, example: HAASAP7) from being used during the entire flow (synthesis onwards). How do I include that specification and in which configuration file? A quick search of the scripts area showed me that there are 3 relevant variables: DONT_USE_LIB, DONT_USE_SC_LIB and DONT_USE_CELLS, but the last one seems to be applicable only to resizer. Don't know what variable to set and where. Please help.

Thanks.

[maliberty]

DONT_USE_CELLS is what you want. There is no way to pass a dont use list to yosys so we have to generate some .lib with the attribute which is what the other variables refer to.

[ishwars1618]

Thanks!
Can you please provide an example of how I can exclude cells that start with a tag, say HA or FA?
I am using ASAP7 libs. Should I hack the .lib files to include an attribute for each such cell in the .lib file?

[ishwars1618]

I also physically removed the information about the cells that should not be used from the asap7 .lib files (under the flow/platforms/asap7/lib directory). A run after this removal still has these cells in the final verilog (and in yosys output verilog - 1_1_yosys.v). Should I remove the information about these cells from other areas as well?

[rovinski]

HA and FA are the adder cells, which have a special mapping routine in yosys. What you want to actually do is actually run make with ADDER_MAP_FILE= which will unset the adder mapping file and disable mapping to adder cells.

Relevant part of the config file:

OpenROAD-flow-scripts/flow/platforms/asap7/config.mk

Line 57 in df9a442

export ADDER_MAP_FILE ?= $(PLATFORM_DIR)/yoSys/cells_adders_R.v

Which affects this part of the script:

OpenROAD-flow-scripts/flow/scripts/synth.tcl

Lines 28 to 37 in df9a442

	# Technology mapping of adders
	if {[info exist ::env(ADDER_MAP_FILE)] && [file isfile $::env(ADDER_MAP_FILE)]} {
	# extract the full adders
	extract_fa
	# map full adders
	techmap -map $::env(ADDER_MAP_FILE)
	techmap
	# Quick optimization
	opt -fast -purge
	}

[ishwars1618]

Thank you! Unsetting that variable worked to ensure HA and FA cells are not used. For not using another combinational cell other than these adder cells, what should I do?

[vijayank88]

Try with this option:

OpenROAD-flow-scripts/flow/platforms/asap7/config.mk

Line 51 in df9a442

export DONT_USE_CELLS += SDF* ICG* DFFH*

[rovinski]

@ishwars1618 Adder cells are the only special ones. For all other cells, you can add them to the DONT_USE_CELLS variable as mentioned. The variable supports wildcards, so you can either use the whole name or a wildcard character * to match all cell names with that pattern.