flow: platforms: sky130: allow PDK path overrides via weak assignment

Convert TECH_LEF, SC_LEF, LIB_FILES, and GDS_FILES from strong (`=`)
to weak (`?=`) assignment so users can substitute a custom PDK version
by setting these variables before including the platform config, without
modifying ORFS-provided files.

Signed-off-by: Daniel Schultz <[email protected]>

Author: dnltz

flow/platforms/sky130hd/config.mk

@@ -4,13 +4,13 @@ export PROCESS = 130
 #-----------------------------------------------------
 # Tech/Libs
 # ----------------------------------------------------
-export TECH_LEF = $(PLATFORM_DIR)/lef/sky130_fd_sc_hd.tlef
-export SC_LEF = $(PLATFORM_DIR)/lef/sky130_fd_sc_hd_merged.lef
+export TECH_LEF ?= $(PLATFORM_DIR)/lef/sky130_fd_sc_hd.tlef
+export SC_LEF ?= $(PLATFORM_DIR)/lef/sky130_fd_sc_hd_merged.lef
 
-export LIB_FILES = $(PLATFORM_DIR)/lib/sky130_fd_sc_hd__tt_025C_1v80.lib \
-                     $(ADDITIONAL_LIBS)
-export GDS_FILES = $(wildcard $(PLATFORM_DIR)/gds/*.gds) \
-                     $(ADDITIONAL_GDS)
+export LIB_FILES ?= $(PLATFORM_DIR)/lib/sky130_fd_sc_hd__tt_025C_1v80.lib
+export LIB_FILES += $(ADDITIONAL_LIBS)
+export GDS_FILES ?= $(wildcard $(PLATFORM_DIR)/gds/*.gds)
+export GDS_FILES += $(ADDITIONAL_GDS)
 
 # Dont use cells to ease congestion
 # Specify at least one filler cell if none

flow/platforms/sky130hs/config.mk

@@ -4,13 +4,13 @@ export PROCESS = 130
 #-----------------------------------------------------
 # Tech/Libs
 # ----------------------------------------------------
-export TECH_LEF = $(PLATFORM_DIR)/lef/sky130_fd_sc_hs.tlef
-export SC_LEF = $(PLATFORM_DIR)/lef/sky130_fd_sc_hs_merged.lef
+export TECH_LEF ?= $(PLATFORM_DIR)/lef/sky130_fd_sc_hs.tlef
+export SC_LEF ?= $(PLATFORM_DIR)/lef/sky130_fd_sc_hs_merged.lef
 
-export LIB_FILES = $(PLATFORM_DIR)/lib/sky130_fd_sc_hs__tt_025C_1v80.lib \
-                     $(ADDITIONAL_LIBS)
-export GDS_FILES = $(wildcard $(PLATFORM_DIR)/gds/*.gds) \
-                     $(ADDITIONAL_GDS)
+export LIB_FILES ?= $(PLATFORM_DIR)/lib/sky130_fd_sc_hs__tt_025C_1v80.lib
+export LIB_FILES += $(ADDITIONAL_LIBS)
+export GDS_FILES ?= $(wildcard $(PLATFORM_DIR)/gds/*.gds)
+export GDS_FILES += $(ADDITIONAL_GDS)
 
 # Dont use cells to ease congestion
 # Specify at least one filler cell if none
@@ -105,4 +105,4 @@ export RCX_RULES = $(PLATFORM_DIR)/rcx_patterns.rules
 export PWR_NETS_VOLTAGES  ?= VDD 1.8
 export GND_NETS_VOLTAGES  ?= VSS 0.0
 export IR_DROP_LAYER ?= met1
-export REMOVE_CELLS_FOR_LEC = sky130_fd_sc_hs__tapvpwrvgnd*
+export REMOVE_CELLS_FOR_LEC = sky130_fd_sc_hs__tapvpwrvgnd*