Modified the deep nwell generation routine to draw the nwell

boundary in four separate rectangles, because the method of
drawing nwell over the area and erasing from the center causes
unexpected/unwanted interactions with any existing layout in
the center of the deep nwell region.

VERSION

@@ -1 +1 @@
-1.0.474
+1.0.475

sky130/magic/sky130.tcl

@@ -549,9 +549,38 @@ proc sky130::deep_nwell_draw {} {
    pushbox
    pushbox
    box grow c 0.4um
+   # Note:  Previous implementation was to draw nwell over the whole
+   # area and then erase it from the center.  That can interact with
+   # any layout already drawn in the center area.  Instead, draw four
+   # separate rectangles.
+   # -----------------
+   # paint nwell
+   # box grow c -1.43um
+   # erase nwell
+   # -----------------
+   pushbox
+   box width 1.43um
+   paint nwell
+   popbox
+   pushbox
+   box height 1.43um
+   paint nwell
+   popbox
+   pushbox
+   box move n ${h}um
+   box move n 0.8um
+   box move s 1.43um
+   box height 1.43um
+   paint nwell
+   popbox
+   pushbox
+   box move e ${w}um
+   box move e 0.8um
+   box move w 1.43um
+   box width 1.43um
    paint nwell
-   box grow c -1.43um
-   erase nwell
+   popbox
+
    popbox
    box grow c 0.03um