diff --git a/fpga_interchange/arch.cc b/fpga_interchange/arch.cc
index e94dab10..71c68e66 100644
--- a/fpga_interchange/arch.cc
+++ b/fpga_interchange/arch.cc
@@ -770,6 +770,7 @@ bool Arch::pack()
     merge_constant_nets();
     pack_ports();
     pack_default_conns();
+    expand_macros();
     return true;
 }
 
diff --git a/fpga_interchange/arch.h b/fpga_interchange/arch.h
index 7188fd36..5c7bbc52 100644
--- a/fpga_interchange/arch.h
+++ b/fpga_interchange/arch.h
@@ -1124,6 +1124,8 @@ struct Arch : ArchAPI<ArchRanges>
 
     const DefaultCellConnsPOD *get_default_conns(IdString cell_type) const;
     void pack_default_conns();
+
+    void expand_macros();
 };
 
 NEXTPNR_NAMESPACE_END
diff --git a/fpga_interchange/macros.cc b/fpga_interchange/macros.cc
new file mode 100644
index 00000000..577671fa
--- /dev/null
+++ b/fpga_interchange/macros.cc
@@ -0,0 +1,113 @@
+/*
+ *  nextpnr -- Next Generation Place and Route
+ *
+ *  Copyright (C) 2021  Symbiflow Authors
+ *
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#include "design_utils.h"
+#include "log.h"
+#include "nextpnr.h"
+#include "util.h"
+
+NEXTPNR_NAMESPACE_BEGIN
+
+static const MacroPOD *lookup_macro(const ChipInfoPOD *chip, IdString cell_type)
+{
+    for (const auto &macro : chip->macros) {
+        if (IdString(macro.name) == cell_type)
+            return &macro;
+    }
+    return nullptr;
+}
+
+static IdString derived_name(Context *ctx, IdString base_name, IdString suffix)
+{
+    return ctx->id(stringf("%s/%s", base_name.c_str(ctx), suffix.c_str(ctx)));
+}
+
+void Arch::expand_macros()
+{
+    // Make up a list of cells, so we don't have modify-while-iterating issues
+    Context *ctx = getCtx();
+    std::vector<CellInfo *> cells;
+    for (auto cell : sorted(ctx->cells))
+        cells.push_back(cell.second);
+
+    std::vector<CellInfo *> next_cells;
+
+    do {
+        // Expand cells
+        for (auto cell : cells) {
+            // TODO: consult exception map
+            const MacroPOD *macro = lookup_macro(chip_info, cell->type);
+            if (macro == nullptr)
+                continue;
+            // Create child instances
+            for (const auto &inst : macro->cell_insts) {
+                CellInfo *inst_cell =
+                        ctx->createCell(derived_name(ctx, cell->name, IdString(inst.name)), IdString(inst.type));
+                for (const auto &param : inst.parameters) {
+                    inst_cell->params[IdString(param.key)] = IdString(param.value).str(ctx);
+                }
+                next_cells.push_back(inst_cell);
+            }
+            // Create and connect nets
+            for (const auto &net_data : macro->nets) {
+                NetInfo *net = nullptr;
+                // If there is a top level port, use that as the net
+                for (const auto &net_port : net_data.ports) {
+                    if (net_port.instance != 0)
+                        continue;
+                    // TODO: case of multiple top level ports on the same net?
+                    NPNR_ASSERT(net == nullptr);
+                    // Use the corresponding pre-expansion port net
+                    net = get_net_or_empty(cell, IdString(net_port.port));
+                    // Disconnect the original port pre-expansion
+                    disconnect_port(ctx, cell, IdString(net_port.port));
+                }
+                // If not on a top level port, create a new net
+                if (net == nullptr)
+                    net = ctx->createNet(derived_name(ctx, cell->name, IdString(net_data.name)));
+                // Create and connect instance ports
+                for (const auto &net_port : net_data.ports) {
+                    if (net_port.instance == 0)
+                        continue;
+                    IdString port_name(net_port.port);
+                    CellInfo *inst_cell =
+                            ctx->cells.at(derived_name(ctx, cell->name, IdString(net_port.instance))).get();
+                    inst_cell->ports[port_name].name = port_name;
+                    inst_cell->ports[port_name].type = PortType(net_port.dir);
+                    connect_port(ctx, net, inst_cell, port_name);
+                }
+            }
+            // TODO: apply parameter rules from exception map
+            // Remove the now-expanded cell, but first make sure we don't leave behind any dangling references
+            for (const auto &port : cell->ports)
+                if (port.second.net != nullptr)
+                    log_error("Macro expansion of %s:%s left dangling port %s.", ctx->nameOf(cell),
+                              ctx->nameOf(cell->type), ctx->nameOf(port.first));
+            ctx->cells.erase(cell->name);
+        }
+
+        // Iterate until no more expansions are possible
+        // The next iteration only needs to look at cells created in this iteration
+        std::swap(next_cells, cells);
+        next_cells.clear();
+    } while (!cells.empty());
+}
+
+NEXTPNR_NAMESPACE_END