Reduce the M4 & M7 PDN pitch for gcd to accommodate its small area

Fixes The-OpenROAD-Project/OpenROAD#7784

Signed-off-by: Matt Liberty <[email protected]>

Author: maliberty

flow/designs/nangate45/gcd/config.mk

@@ -12,3 +12,6 @@ export CORE_UTILIZATION ?= 55
 export PLACE_DENSITY_LB_ADDON = 0.20
 export TNS_END_PERCENT        = 100
 export REMOVE_CELLS_FOR_EQY   = TAPCELL*
+
+# This needs a smaller pitch to accomodate a small block
+export PDN_TCL ?= $(DESIGN_HOME)/$(PLATFORM)/$(DESIGN_NAME)/grid_strategy-M1-M4-M7.tcl

flow/designs/nangate45/gcd/grid_strategy-M1-M4-M7.tcl

@@ -0,0 +1,22 @@
+####################################
+# global connections
+####################################
+add_global_connection -net {VDD} -inst_pattern {.*} -pin_pattern {^VDD$} -power
+add_global_connection -net {VDD} -inst_pattern {.*} -pin_pattern {^VDDPE$}
+add_global_connection -net {VDD} -inst_pattern {.*} -pin_pattern {^VDDCE$}
+add_global_connection -net {VSS} -inst_pattern {.*} -pin_pattern {^VSS$} -ground
+add_global_connection -net {VSS} -inst_pattern {.*} -pin_pattern {^VSSE$}
+global_connect
+####################################
+# voltage domains
+####################################
+set_voltage_domain -name {CORE} -power {VDD} -ground {VSS}
+####################################
+# standard cell grid
+####################################
+define_pdn_grid -name {grid} -voltage_domains {CORE}
+add_pdn_stripe -grid {grid} -layer {metal1} -width {0.17} -pitch {2.4} -offset {0} -followpins
+add_pdn_stripe -grid {grid} -layer {metal4} -width {0.48} -pitch {28.0} -offset {2}
+add_pdn_stripe -grid {grid} -layer {metal7} -width {1.40} -pitch {15.0} -offset {2}
+add_pdn_connect -grid {grid} -layers {metal1 metal4}
+add_pdn_connect -grid {grid} -layers {metal4 metal7}