After functional ECO, the ECO patch can be synthesized to map to the spare gates. The spare gates list is combination of two inputs AND/OR/NAND/NOR/INV and flops, MUX being optional.
The synthesis can be constrained to control the spare gates type and number being used. The API set_constraint is to set constraint on spare cells type or spare cells number.
We will show that the optimal spare gates list is all AND/OR/NAND/NOR being in the list. The example is to map AIO222X2 to different combinations of spare gates.
The following ECO script is to map AOI222X2 to AND2X1 and NOR2X1 types.
# LEC script, map_spare_cells_example.pl use strict; read_library("art.5nm.lib"); # Read in standard library read_design('-imp', 'imp_net.v'); change_port("out", "AOI222X2", "", "a,b,c,d,e,f"); set_constraints("-type", "AND2X1,INVX1,NOR2X1"); # Map to AND2X1/NOR2X1/INVX1 map_spare_cells; write_verilog("mapped_verilog.v");
As shown in the Figure 1, 3 AND gates and 2 NOR are mapped in the final circuit.
Figure 1: Map Spare Cells to AND and NOR
The following ECO script sets constraint to use only one AND.
# LEC script, map_spare_cells_example.pl use strict; read_library("art.5nm.lib"); # Read in standard library read_design('-imp', 'imp_net.v'); change_port("out", "AOI222X2", "", "a,b,c,d,e,f"); set_constraints("-type", "AND2X1,INVX1,NOR2X1"); set_constraints("-num", "and<2"); # Force to have only one 'and' type map_spare_cells; write_verilog("mapped_verilog.v");
As shown in the Figure 2, 1 AND gates and 4 NOR are mapped in the final circuit. But 4 extra inverts are inserted.
Figure 2: Map Spare Cells to One AND and Multiple NOR
The following ECO script sets constraint to use only NAND type.
# LEC script, map_spare_cells_example.pl use strict; read_library("art.5nm.lib"); # Read in standard library read_design('-imp', 'imp_net.v'); change_port("out", "AOI222X2", "", "a,b,c,d,e,f"); set_constraints("-type", "INVX1,NAND2X1"); # Map to NAND2X1/INVX1 map_spare_cells; write_verilog("mapped_verilog.v");
Figure 3: Map Spare Cells to NAND
From the above experimental runs, the best constraint is to have spare cells type NAND, OR and NOR.
# LEC script, map_spare_cells_example.pl use strict; read_library("art.5nm.lib"); # Read in standard library read_design('-imp', 'imp_net.v'); change_port("out", "AOI222X2", "", "a,b,c,d,e,f"); set_constraints("-type", "AND2X1,INVX1,NOR2X1,OR2X1"); # Map to AND/OR/NOR map_spare_cells; write_verilog("mapped_verilog.v");
As shown in the Figure 4, 3 AND, one OR and one NOR are used and no invert is used in this mapping.
Figure 4: Map Spare Cells to NAND
So the conclusion for the optimal spare gates list is, it should have AND/OR/NAND/NOR types spare gates. This will make synthesis work in most efficient way and ECO patch size is the smallest.
Check Metal Only ECO for detail
