ice40: Pack constants to LCs

Signed-off-by: David Shah <davey1576@gmail.com>

ice40/blinky_nopack.ys

@@ -1,3 +1,3 @@
 read_verilog blinky.v
 synth_ice40 -nocarry -top blinky
-write_json blinky.json
+write_json blinky_nopack.json

ice40/blinky_noyspack.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+set -ex
+yosys blinky_nopack.ys
+../nextpnr-ice40 --json blinky_nopack.json --asc blinky.asc --pack
+icepack blinky.asc blinky.bin
+icebox_vlog blinky.asc > blinky_chip.v
+iverilog -o blinky_tb blinky_chip.v blinky_tb.v
+vvp -N ./blinky_tb

ice40/icebreaker.ys

@@ -1,9 +1,3 @@
 read_verilog icebreaker.v
-read_verilog -lib +/ice40/cells_sim.v
+synth_ice40 -nocarry -top icebreaker
-synth -top icebreaker
-abc -lut 4
-techmap -map blinky_map.v
-splitnets
-opt_clean
-stat
 write_json icebreaker.json

ice40/pack.cc

@@ -89,9 +89,34 @@ static void pack_nonlut_ffs(Design *design)
     }
 }
 
+// Pack constants (simple implementation)
+static void pack_constants(Design *design) {
+    CellInfo *gnd_cell = create_ice_cell(design, "ICESTORM_LC",
+                                       "$PACKER_GND");
+    gnd_cell->attrs["LUT_INIT"] = "0";
+
+    CellInfo *vcc_cell = create_ice_cell(design, "ICESTORM_LC",
+                                         "$PACKER_VCC");
+    vcc_cell->attrs["LUT_INIT"] = "1";
+
+    for (auto net : design->nets) {
+        NetInfo *ni = net.second;
+        if (ni->driver.cell != nullptr && ni->driver.cell->type == "GND") {
+            ni->driver.cell = gnd_cell;
+            ni->driver.port = "O";
+            design->cells[gnd_cell->name] = gnd_cell;
+        } else if (ni->driver.cell != nullptr && ni->driver.cell->type == "VCC") {
+            ni->driver.cell = vcc_cell;
+            ni->driver.port = "O";
+            design->cells[vcc_cell->name] = vcc_cell;
+        }
+    }
+}
+
 // Main pack function
 void pack_design(Design *design)
 {
+    pack_constants(design);
     pack_lut_lutffs(design);
     pack_nonlut_ffs(design);
 }