Added a new custom cell for fill_12 in the sky130 HD standard cell li…

…brary that

can be used to replace decap_12 cells to reduce the amount of poly in a standard
cell layout to conform to the new and tighter poly layer density of 38%.

sky130/custom/sky130_fd_sc_hd/Readme.txt

@@ -1,3 +1,5 @@
 These decap cells were redesigned to cut back on its use of the LI layer because the corresponding SkyWater cell was covered in something like 70-80% LI, and using enough of the decap in any one design would cause an LI density error.
 
-The fill cells were redesigned to add tap diffusion in the middle because otherwise the spacing of the nwells and the height of the cells prevents FOM fill, resulting in a different density error.
+The fill cells were redesigned to add tap diffusion in the middle because otherwise the spacing of the nwells and the height of the cells prevents FOM fill, resulting in a different density error.
+
+Cell "newfill_12" was added to satisfy the change in the poly density rule to 38%;  this cell is effectively the decap_12 cell with the poly removed, rendering it a fill cell.  Its use is to replace some percentage of decap_12 cells until the maximum poly density rule is satisfied.

sky130/custom/sky130_fd_sc_hd/lef/sky130_ef_sc_hd__newfill_12.lef

@@ -0,0 +1,79 @@
+VERSION 5.7 ;
+  NOWIREEXTENSIONATPIN ON ;
+  DIVIDERCHAR "/" ;
+  BUSBITCHARS "[]" ;
+MACRO sky130_ef_sc_hd__newfill_12
+  CLASS CORE SPACER ;
+  FOREIGN sky130_ef_sc_hd__newfill_12 ;
+  ORIGIN 0.000 0.000 ;
+  SIZE 5.520 BY 2.720 ;
+  SYMMETRY X Y R90 ;
+  SITE unithd ;
+  PIN VPWR
+    USE POWER ;
+    PORT
+      LAYER met1 ;
+        RECT 0.000 2.480 5.520 2.960 ;
+    END
+  END VPWR
+  PIN VGND
+    USE GROUND ;
+    PORT
+      LAYER met1 ;
+        RECT 0.000 -0.240 5.520 0.240 ;
+    END
+  END VGND
+  PIN VPB
+    DIRECTION INOUT ;
+    USE POWER ;
+    PORT
+      LAYER nwell ;
+        RECT -0.190 1.305 5.710 2.910 ;
+    END
+  END VPB
+  PIN VNB
+    DIRECTION INOUT ;
+    USE GROUND ;
+    PORT
+      LAYER pwell ;
+        RECT 0.005 0.105 5.515 0.915 ;
+        RECT 0.145 -0.085 0.315 0.105 ;
+    END
+  END VNB
+  OBS
+      LAYER li1 ;
+        RECT 0.000 2.635 5.520 2.805 ;
+        RECT 0.085 2.200 5.430 2.635 ;
+        RECT 1.670 0.630 2.010 1.460 ;
+        RECT 3.490 0.950 3.840 2.200 ;
+        RECT 0.085 0.085 5.430 0.630 ;
+        RECT 0.000 -0.085 5.520 0.085 ;
+      LAYER mcon ;
+        RECT 0.145 2.635 0.315 2.805 ;
+        RECT 0.605 2.635 0.775 2.805 ;
+        RECT 1.065 2.635 1.235 2.805 ;
+        RECT 1.525 2.635 1.695 2.805 ;
+        RECT 1.985 2.635 2.155 2.805 ;
+        RECT 2.445 2.635 2.615 2.805 ;
+        RECT 2.905 2.635 3.075 2.805 ;
+        RECT 3.365 2.635 3.535 2.805 ;
+        RECT 3.825 2.635 3.995 2.805 ;
+        RECT 4.285 2.635 4.455 2.805 ;
+        RECT 4.745 2.635 4.915 2.805 ;
+        RECT 5.205 2.635 5.375 2.805 ;
+        RECT 0.145 -0.085 0.315 0.085 ;
+        RECT 0.605 -0.085 0.775 0.085 ;
+        RECT 1.065 -0.085 1.235 0.085 ;
+        RECT 1.525 -0.085 1.695 0.085 ;
+        RECT 1.985 -0.085 2.155 0.085 ;
+        RECT 2.445 -0.085 2.615 0.085 ;
+        RECT 2.905 -0.085 3.075 0.085 ;
+        RECT 3.365 -0.085 3.535 0.085 ;
+        RECT 3.825 -0.085 3.995 0.085 ;
+        RECT 4.285 -0.085 4.455 0.085 ;
+        RECT 4.745 -0.085 4.915 0.085 ;
+        RECT 5.205 -0.085 5.375 0.085 ;
+  END
+END sky130_ef_sc_hd__newfill_12
+END LIBRARY
+

sky130/custom/sky130_fd_sc_hd/verilog/sky130_ef_sc_hd__newfill_12.v

@@ -0,0 +1,71 @@
+/**
+ * Copyright 2020 The SkyWater PDK Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+`ifndef SKY130_EF_SC_HD__NEWFILL_12_V
+`define SKY130_EF_SC_HD__NEWFILL_12_V
+
+/**
+ * newfill_12:  Designed to replace the decap_12 cell while reducing
+ * the amount of local interconnect and satisfying the more restrictive
+ * poly density rule of 38%.
+ */
+
+`timescale 1ns / 1ps
+`default_nettype none
+
+
+`ifdef USE_POWER_PINS
+/*********************************************************/
+
+`celldefine
+module sky130_ef_sc_hd__newfill_12 (
+    VPWR,
+    VGND,
+    VPB ,
+    VNB
+);
+
+    input VPWR;
+    input VGND;
+    input VPB ;
+    input VNB ;
+    // No contents.
+endmodule
+`endcelldefine
+
+/*********************************************************/
+`else // If not USE_POWER_PINS
+/*********************************************************/
+
+`celldefine
+module sky130_ef_sc_hd__newfill_12 ();
+
+    // Voltage supply signals
+    supply1 VPWR;
+    supply0 VGND;
+    supply1 VPB ;
+    supply0 VNB ;
+    // No contents.
+endmodule
+`endcelldefine
+
+/*********************************************************/
+`endif // USE_POWER_PINS
+
+`default_nettype wire
+`endif  // SKY130_EF_SC_HD__NEWFILL_12_V