synth_ice40: use 4-LUT coarse synthesis mode.

diff --git a/techlibs/ice40/synth_ice40.cc b/techlibs/ice40/synth_ice40.cc
index c2aed873bbb11fc1c5761fc967853c73ad7ccdb3..4c4fdf7beaa64d5516764100effeadf73db235f6 100644 (file)
--- a/techlibs/ice40/synth_ice40.cc
+++ b/techlibs/ice40/synth_ice40.cc
@@ -226,7 +226,7 @@ struct SynthIce40Pass : public ScriptPass
 
                if (check_label("coarse"))
                {
-                       run("synth -run coarse");
+                       run("synth -lut 4 -run coarse");
                }
 
                if (!nobram && check_label("bram", "(skip if -nobram)"))