ecp5: Add simple constant packer

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

ecp5/archdefs.h

@@ -129,8 +129,12 @@ struct DecalId
     }
 };
 
-struct ArchNetInfo { };
+struct ArchNetInfo
-struct ArchCellInfo { };
+{
+};
+struct ArchCellInfo
+{
+};
 
 NEXTPNR_NAMESPACE_END
 

ecp5/cells.cc

@@ -116,6 +116,14 @@ std::unique_ptr<CellInfo> create_ecp5_cell(Context *ctx, IdString type, std::str
         add_port(ctx, new_cell.get(), "I", PORT_IN);
         add_port(ctx, new_cell.get(), "T", PORT_IN);
         add_port(ctx, new_cell.get(), "O", PORT_OUT);
+    } else if (type == ctx->id("LUT4")) {
+        new_cell->params[ctx->id("INIT")] = "0";
+
+        add_port(ctx, new_cell.get(), "A", PORT_IN);
+        add_port(ctx, new_cell.get(), "B", PORT_IN);
+        add_port(ctx, new_cell.get(), "C", PORT_IN);
+        add_port(ctx, new_cell.get(), "D", PORT_IN);
+        add_port(ctx, new_cell.get(), "Z", PORT_OUT);
     } else {
         log_error("unable to create ECP5 cell of type %s", type.c_str(ctx));
     }

ecp5/pack.cc

@@ -385,10 +385,94 @@ class Ecp5Packer
         cell->ports.at(input).net = nullptr;
     }
 
+    // Merge a net into a constant net
+    void set_net_constant(const Context *ctx, NetInfo *orig, NetInfo *constnet, bool constval)
+    {
+        orig->driver.cell = nullptr;
+        for (auto user : orig->users) {
+            if (user.cell != nullptr) {
+                CellInfo *uc = user.cell;
+                if (ctx->verbose)
+                    log_info("%s user %s\n", orig->name.c_str(ctx), uc->name.c_str(ctx));
+                if (is_lut(ctx, uc)) {
+                    set_lut_input_constant(uc, user.port, constval);
+                } else if (is_ff(ctx, uc) && user.port == ctx->id("CE")) {
+                    uc->params[ctx->id("CEMUX")] = constval ? "1" : "0";
+                    uc->ports[user.port].net = nullptr;
+                } else if (is_ff(ctx, uc) && user.port == ctx->id("LSR") &&
+                           ((!constval && str_or_default(uc->params, ctx->id("LSRMUX"), "LSR") == "LSR") ||
+                            (constval && str_or_default(uc->params, ctx->id("LSRMUX"), "LSR") == "INV"))) {
+                    uc->ports[user.port].net = nullptr;
+                } else {
+                    uc->ports[user.port].net = constnet;
+                    constnet->users.push_back(user);
+                }
+            }
+        }
+        orig->users.clear();
+    }
+
+    // Pack constants (simple implementation)
+    void pack_constants()
+    {
+        log_info("Packing constants..\n");
+
+        std::unique_ptr<CellInfo> gnd_cell = create_ecp5_cell(ctx, ctx->id("LUT4"), "$PACKER_GND");
+        gnd_cell->params[ctx->id("LUT_INIT")] = "0";
+        std::unique_ptr<NetInfo> gnd_net = std::unique_ptr<NetInfo>(new NetInfo);
+        gnd_net->name = ctx->id("$PACKER_GND_NET");
+        gnd_net->driver.cell = gnd_cell.get();
+        gnd_net->driver.port = ctx->id("Z");
+        gnd_cell->ports.at(ctx->id("Z")).net = gnd_net.get();
+
+        std::unique_ptr<CellInfo> vcc_cell = create_ecp5_cell(ctx, ctx->id("LUT4"), "$PACKER_VCC");
+        vcc_cell->params[ctx->id("LUT_INIT")] = "65535";
+        std::unique_ptr<NetInfo> vcc_net = std::unique_ptr<NetInfo>(new NetInfo);
+        vcc_net->name = ctx->id("$PACKER_VCC_NET");
+        vcc_net->driver.cell = vcc_cell.get();
+        vcc_net->driver.port = ctx->id("Z");
+        vcc_cell->ports.at(ctx->id("Z")).net = vcc_net.get();
+
+        std::vector<IdString> dead_nets;
+
+        bool gnd_used = false, vcc_used = false;
+
+        for (auto net : sorted(ctx->nets)) {
+            NetInfo *ni = net.second;
+            if (ni->driver.cell != nullptr && ni->driver.cell->type == ctx->id("GND")) {
+                IdString drv_cell = ni->driver.cell->name;
+                set_net_constant(ctx, ni, gnd_net.get(), false);
+                gnd_used = true;
+                dead_nets.push_back(net.first);
+                ctx->cells.erase(drv_cell);
+            } else if (ni->driver.cell != nullptr && ni->driver.cell->type == ctx->id("VCC")) {
+                IdString drv_cell = ni->driver.cell->name;
+                set_net_constant(ctx, ni, vcc_net.get(), true);
+                vcc_used = true;
+                dead_nets.push_back(net.first);
+                ctx->cells.erase(drv_cell);
+            }
+        }
+
+        if (gnd_used) {
+            ctx->cells[gnd_cell->name] = std::move(gnd_cell);
+            ctx->nets[gnd_net->name] = std::move(gnd_net);
+        }
+        if (vcc_used) {
+            ctx->cells[vcc_cell->name] = std::move(vcc_cell);
+            ctx->nets[vcc_net->name] = std::move(vcc_net);
+        }
+
+        for (auto dn : dead_nets) {
+            ctx->nets.erase(dn);
+        }
+    }
+
   public:
     void pack()
     {
         pack_io();
+        pack_constants();
         find_lutff_pairs();
         pack_lut5s();
         pair_luts();