diff --git a/gateware/e1-tracer/Makefile b/gateware/e1-tracer/Makefile
index e3d08b8..5718966 100644
--- a/gateware/e1-tracer/Makefile
+++ b/gateware/e1-tracer/Makefile
@@ -29,10 +29,15 @@
 
 # Target config
 BOARD ?= e1-tracer
-DEVICE = up5k
-PACKAGE = sg48
+DEVICE := up5k
+PACKAGE := sg48
 
-NEXTPNR_ARGS = --pre-pack data/clocks.py --seed 19
+SEED ?= 19
+NEXTPNR_ARGS := --no-promote-globals --pre-pack data/clocks.py --seed $(SEED)
+
+ifeq ($(IGNORE_TIMING),1)
+	NEXTPNR_ARGS += --timing-allow-fail
+endif
 
 # Include default rules
 NO2BUILD_DIR ?= ../build
diff --git a/gateware/icE1usb-proto/Makefile b/gateware/icE1usb-proto/Makefile
index d17a540..31692a4 100644
--- a/gateware/icE1usb-proto/Makefile
+++ b/gateware/icE1usb-proto/Makefile
@@ -29,10 +29,15 @@
 
 # Target config
 BOARD ?= icebreaker
-DEVICE = up5k
-PACKAGE = sg48
+DEVICE := up5k
+PACKAGE := sg48
 
-NEXTPNR_ARGS = --pre-pack data/clocks.py --seed 4
+SEED ?= 4
+NEXTPNR_ARGS := --no-promote-globals --pre-pack data/clocks.py --seed $(SEED)
+
+ifeq ($(IGNORE_TIMING),1)
+	NEXTPNR_ARGS += --timing-allow-fail
+endif
 
 # Include default rules
 NO2BUILD_DIR ?= ../build
diff --git a/gateware/icE1usb/Makefile b/gateware/icE1usb/Makefile
index 0904660..dcafe27 100644
--- a/gateware/icE1usb/Makefile
+++ b/gateware/icE1usb/Makefile
@@ -33,11 +33,16 @@
 
 # Target config
 BOARD ?= ice1usb
-DEVICE = up5k
-PACKAGE = sg48
+DEVICE := up5k
+PACKAGE := sg48
 
 YOSYS_SYNTH_ARGS = -dffe_min_ce_use 4
-NEXTPNR_ARGS = --pre-pack data/clocks.py --no-promote-globals --seed 2
+SEED ?= 15
+NEXTPNR_ARGS := --no-promote-globals --pre-pack data/clocks.py --seed $(SEED)
+
+ifeq ($(IGNORE_TIMING),1)
+	NEXTPNR_ARGS += --timing-allow-fail
+endif
 
 # Include default rules
 NO2BUILD_DIR ?= ../build