Add initial logic for handling dedicated interconnect situations.

Signed-off-by: Keith Rothman <537074+litghost@users.noreply.github.com>

11 files changed, 587 insertions, 26 deletions

diff --git a/fpga_interchange/arch.cc b/fpga_interchange/arch.cc
index 4cffd6ca..0955c376 100644
--- a/fpga_interchange/arch.cc
+++ b/fpga_interchange/arch.cc
@@ -195,6 +195,11 @@ Arch::Arch(ArchArgs args) : args(args)
     default_tags.resize(max_tag_count);
 }
 
+
+void Arch::init() {
+    dedicated_interconnect.init(getCtx());
+}
+
 // -----------------------------------------------------------------------
 
 std::string Arch::getChipName() const { return chip_info->name.get(); }
diff --git a/fpga_interchange/arch.h b/fpga_interchange/arch.h
index a5352b60..780382ec 100644
--- a/fpga_interchange/arch.h
+++ b/fpga_interchange/arch.h
@@ -29,6 +29,7 @@
 #include <iostream>
 
 #include "constraints.h"
+#include "dedicated_interconnect.h"
 
 NEXTPNR_NAMESPACE_BEGIN
 
@@ -772,6 +773,8 @@ struct ArchRanges
     using BucketBelRangeT = FilteredBelRange;
 };
 
+struct DedicatedInterconnect;
+
 struct Arch : ArchAPI<ArchRanges>
 {
     boost::iostreams::mapped_file_source blob_file;
@@ -783,8 +786,6 @@ struct Arch : ArchAPI<ArchRanges>
 
     std::unordered_map<WireId, NetInfo *> wire_to_net;
     std::unordered_map<PipId, NetInfo *> pip_to_net;
-    std::unordered_map<WireId, std::pair<int, int>> driving_pip_loc;
-    std::unordered_map<WireId, NetInfo *> reserved_wires;
 
     static constexpr size_t kMaxState = 8;
 
@@ -811,10 +812,12 @@ struct Arch : ArchAPI<ArchRanges>
         std::vector<SiteRouter> sites;
     };
 
+    DedicatedInterconnect dedicated_interconnect;
     std::unordered_map<int32_t, TileStatus> tileStatus;
 
     ArchArgs args;
     Arch(ArchArgs args);
+    void init();
 
     std::string getChipName() const override;
 
@@ -1236,9 +1239,6 @@ struct Arch : ArchAPI<ArchRanges>
         NPNR_ASSERT(wire_to_net[dst] == nullptr || wire_to_net[dst] == net);
 
         pip_to_net[pip] = net;
-        std::pair<int, int> loc;
-        get_tile_x_y(pip.tile, &loc.first, &loc.second);
-        driving_pip_loc[dst] = loc;
 
         wire_to_net[dst] = net;
         net->wires[dst].pip = pip;
@@ -1509,6 +1509,10 @@ struct Arch : ArchAPI<ArchRanges>
         if (cell == nullptr) {
             return true;
         } else {
+            if(!dedicated_interconnect.isBelLocationValid(bel, cell)) {
+                return false;
+            }
+
             if (io_port_types.count(cell->type)) {
                 // FIXME: Probably need to actually constraint io port cell/bel,
                 // but the current BBA emission doesn't support that.  This only
diff --git a/fpga_interchange/dedicated_interconnect.cc b/fpga_interchange/dedicated_interconnect.cc
new file mode 100644
index 00000000..82101fbd
--- /dev/null
+++ b/fpga_interchange/dedicated_interconnect.cc
@@ -0,0 +1,351 @@
+/*
+ *  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 "nextpnr.h"
+#include "log.h"
+#include "util.h"
+
+NEXTPNR_NAMESPACE_BEGIN
+
+void DedicatedInterconnect::init(const Context *ctx) {
+    this->ctx = ctx;
+
+    if(ctx->debug) {
+        log_info("Finding dedicated interconnect!\n");
+    }
+
+    find_dedicated_interconnect();
+    if(ctx->debug) {
+        print_dedicated_interconnect();
+    }
+}
+
+bool DedicatedInterconnect::check_routing(
+        BelId src_bel, IdString src_bel_pin,
+        BelId dst_bel, IdString dst_bel_pin) const {
+    // FIXME: Implement.
+    return false;
+}
+
+bool DedicatedInterconnect::isBelLocationValid(BelId bel, const CellInfo* cell) const {
+    NPNR_ASSERT(bel != BelId());
+
+    Loc bel_loc = ctx->getBelLocation(bel);
+
+    const auto &bel_data = bel_info(ctx->chip_info, bel);
+
+    for(const auto &port_pair : cell->ports) {
+        IdString port_name = port_pair.first;
+        NetInfo *net = port_pair.second.net;
+        if(net == nullptr) {
+            continue;
+        }
+
+        // Only check sink BELs.
+        if(net->driver.cell == cell && net->driver.port == port_name) {
+            continue;
+        }
+
+        // This net doesn't have a driver, probably not valid?
+        NPNR_ASSERT(net->driver.cell != nullptr);
+
+        BelId driver_bel = net->driver.cell->bel;
+        if(driver_bel == BelId()) {
+            return true;
+        }
+
+        const auto &driver_bel_data = bel_info(ctx->chip_info, driver_bel);
+
+        Loc driver_loc = ctx->getBelLocation(driver_bel);
+
+        DeltaTileTypeBelPin driver_type_bel_pin;
+        driver_type_bel_pin.delta_x = driver_loc.x - bel_loc.x;
+        driver_type_bel_pin.delta_y = driver_loc.y - bel_loc.y;
+        driver_type_bel_pin.type_bel_pin.tile_type = ctx->chip_info->tiles[driver_bel.tile].type;
+        driver_type_bel_pin.type_bel_pin.bel_index = driver_bel.index;
+        driver_type_bel_pin.type_bel_pin.bel_pin = get_only_value(ctx->getBelPinsForCellPin(net->driver.cell, net->driver.port));
+
+        for(IdString bel_pin : ctx->getBelPinsForCellPin(cell, port_name)) {
+            TileTypeBelPin type_bel_pin;
+            type_bel_pin.tile_type = ctx->chip_info->tiles[bel.tile].type;
+            type_bel_pin.bel_index = bel.index;
+            type_bel_pin.bel_pin = bel_pin;
+
+            auto iter = pins_with_dedicate_interconnect.find(type_bel_pin);
+            if(iter == pins_with_dedicate_interconnect.end()) {
+                // This BEL pin doesn't have a dedicate interconnect.
+                continue;
+            }
+
+            if(bel.tile == driver_bel.tile && bel_data.site == driver_bel_data.site) {
+                // This is a site local routing, even though this is a sink
+                // with a dedicated interconnect.
+                continue;
+            }
+
+            // Do fast routing check to see if the pair of driver and sink
+            // every are valid.
+            if(iter->second.count(driver_type_bel_pin) == 0) {
+                if(ctx->verbose) {
+                    log_info("BEL %s is not valid because pin %s cannot be driven by %s/%s\n",
+                            ctx->nameOfBel(bel),
+                            bel_pin.c_str(ctx),
+                            ctx->nameOfBel(driver_bel),
+                            driver_type_bel_pin.type_bel_pin.bel_pin.c_str(ctx));
+                }
+                return false;
+            }
+
+            // Do detailed routing check to ensure driver can reach sink.
+            //
+            // FIXME: This might be too slow, but it handles a case on
+            // SLICEL.COUT -> SLICEL.CIN has delta_y = {1, 2}, but the
+            // delta_y=2 case is rare.
+            if(!check_routing(
+                    driver_bel, driver_type_bel_pin.type_bel_pin.bel_pin,
+                    bel, bel_pin)) {
+                if(ctx->verbose) {
+                    log_info("BEL %s is not valid because pin %s cannot be driven by %s/%s (via detailed check)\n",
+                            ctx->nameOfBel(bel),
+                            bel_pin.c_str(ctx),
+                            ctx->nameOfBel(driver_bel),
+                            driver_type_bel_pin.type_bel_pin.bel_pin.c_str(ctx));
+                }
+                return false;
+            }
+        }
+    }
+
+    return true;
+}
+
+void DedicatedInterconnect::print_dedicated_interconnect() const {
+    log_info("Found %zu sinks with dedicated interconnect\n", pins_with_dedicate_interconnect.size());
+    std::vector<TileTypeBelPin> sorted_keys;
+    for(const auto & sink_to_srcs : pins_with_dedicate_interconnect) {
+        sorted_keys.push_back(sink_to_srcs.first);
+    }
+    std::sort(sorted_keys.begin(), sorted_keys.end());
+
+    for(const auto & dst : sorted_keys) {
+        for(const auto & src : pins_with_dedicate_interconnect.at(dst)) {
+            const TileTypeInfoPOD & src_tile_type = ctx->chip_info->tile_types[src.type_bel_pin.tile_type];
+            const BelInfoPOD & src_bel_info = src_tile_type.bel_data[src.type_bel_pin.bel_index];
+            IdString src_site_type = IdString(src_tile_type.site_types[src_bel_info.site]);
+            IdString src_bel_pin = src.type_bel_pin.bel_pin;
+
+            const TileTypeInfoPOD & dst_tile_type = ctx->chip_info->tile_types[dst.tile_type];
+            const BelInfoPOD & dst_bel_info = dst_tile_type.bel_data[dst.bel_index];
+            IdString dst_site_type = IdString(dst_tile_type.site_types[dst_bel_info.site]);
+            IdString dst_bel_pin = dst.bel_pin;
+
+            log_info("%s.%s/%s/%s (%d, %d) -> %s.%s/%s/%s\n",
+                    IdString(src_tile_type.name).c_str(ctx),
+                    src_site_type.c_str(ctx),
+                    IdString(src_bel_info.name).c_str(ctx),
+                    src_bel_pin.c_str(ctx),
+                    src.delta_x,
+                    src.delta_y,
+                    IdString(dst_tile_type.name).c_str(ctx),
+                    dst_site_type.c_str(ctx),
+                    IdString(dst_bel_info.name).c_str(ctx),
+                    dst_bel_pin.c_str(ctx));
+
+        }
+    }
+}
+
+void DedicatedInterconnect::find_dedicated_interconnect() {
+    for(BelId bel : ctx->getBels()) {
+        const auto & bel_data = bel_info(ctx->chip_info, bel);
+        if(bel_data.category != BEL_CATEGORY_LOGIC) {
+            continue;
+        }
+        if(bel_data.synthetic) {
+            continue;
+        }
+
+        for(size_t i = 0; i < bel_data.num_bel_wires; ++i) {
+            if(bel_data.types[i] != PORT_IN) {
+                continue;
+            }
+
+            WireId wire;
+            wire.tile = bel.tile;
+            wire.index = bel_data.wires[i];
+
+            expand_bel(bel, IdString(bel_data.ports[i]), wire);
+        }
+    }
+}
+
+// All legal routes involved at most 2 sites, the source site and the sink
+// site.  The source site and sink sites may be the same, but that is not
+// dedicated routing, that is intra site routing.
+//
+// Dedicated routing must leave the sink site, traverse some routing and
+// terminate at another site.  Routing that "flys" over a site is expressed as
+// a psuedo-pip connected the relevant site pin wires, rather than traversing
+// the site.
+enum WireNodeState {
+    IN_SINK_SITE = 0,
+    IN_ROUTING = 1,
+    IN_SOURCE_SITE = 2
+};
+
+struct WireNode {
+    WireId wire;
+    WireNodeState state;
+    int depth;
+};
+
+// Maximum depth that a dedicate interconnect is considered.
+//
+// Routing networks with depth <= kMaxDepth is considers a dedicated
+// interconnect.
+constexpr int kMaxDepth = 20;
+
+void DedicatedInterconnect::expand_bel(BelId bel, IdString pin, WireId wire) {
+    NPNR_ASSERT(bel != BelId());
+
+    std::vector<WireNode> nodes_to_expand;
+
+    const auto & src_wire_data = ctx->wire_info(wire);
+    NPNR_ASSERT(src_wire_data.site != -1);
+
+    WireNode wire_node;
+    wire_node.wire = wire;
+    wire_node.state = IN_SINK_SITE;
+    wire_node.depth = 0;
+
+    nodes_to_expand.push_back(wire_node);
+
+    Loc sink_loc = ctx->getBelLocation(bel);
+    std::unordered_set<DeltaTileTypeBelPin> srcs;
+
+    while(!nodes_to_expand.empty()) {
+        WireNode node_to_expand = nodes_to_expand.back();
+        nodes_to_expand.pop_back();
+
+        for(PipId pip : ctx->getPipsUphill(node_to_expand.wire)) {
+            if(ctx->is_pip_synthetic(pip)) {
+                continue;
+            }
+
+            WireId wire = ctx->getPipSrcWire(pip);
+            if(wire == WireId()) {
+                continue;
+            }
+
+            WireNode next_node;
+            next_node.wire = wire;
+            next_node.depth = node_to_expand.depth += 1;
+
+            if(next_node.depth > kMaxDepth) {
+                // Dedicated routing should reach sources by kMaxDepth (with
+                // tuning).
+                //
+                // FIXME: Consider removing kMaxDepth and use kMaxSources?
+                return;
+            }
+
+            auto const & wire_data = ctx->wire_info(wire);
+
+            bool expand_node = true;
+            if(ctx->is_site_port(pip)) {
+                switch(node_to_expand.state) {
+                    case IN_SINK_SITE:
+                        NPNR_ASSERT(wire_data.site == -1);
+                        next_node.state = IN_ROUTING;
+                        break;
+                    case IN_ROUTING:
+                        NPNR_ASSERT(wire_data.site != -1);
+                        if(wire_data.site == src_wire_data.site) {
+                            // Dedicated routing won't have straight loops,
+                            // general routing looks like that.
+                            return;
+                        }
+                        next_node.state = IN_SOURCE_SITE;
+                        break;
+                    case IN_SOURCE_SITE:
+                        // Once entering a site, do not leave it again.
+                        // This path is not a legal route!
+                        expand_node = false;
+                        break;
+                    default:
+                        // Unreachable!!!
+                        NPNR_ASSERT(false);
+                }
+            } else {
+                next_node.state = node_to_expand.state;
+            }
+
+            if(expand_node) {
+                nodes_to_expand.push_back(next_node);
+            } else {
+                continue;
+            }
+
+            if(next_node.state == IN_SOURCE_SITE) {
+                for(BelPin bel_pin : ctx->getWireBelPins(wire)) {
+                    BelId src_bel = bel_pin.bel;
+                    auto const & bel_data = bel_info(ctx->chip_info, src_bel);
+                    NPNR_ASSERT(bel_data.site != src_wire_data.site);
+
+                    if(bel_data.category != BEL_CATEGORY_LOGIC) {
+                        continue;
+                    }
+                    if(bel_data.synthetic) {
+                        continue;
+                    }
+                    if(ctx->getBelPinType(bel_pin.bel, bel_pin.pin) != PORT_OUT) {
+                        continue;
+                    }
+
+                    Loc src_loc = ctx->getBelLocation(src_bel);
+
+                    DeltaTileTypeBelPin delta_type_bel_pin;
+                    delta_type_bel_pin.delta_x = src_loc.x - sink_loc.x;
+                    delta_type_bel_pin.delta_x = src_loc.y - sink_loc.y;
+                    delta_type_bel_pin.type_bel_pin.tile_type = ctx->chip_info->tiles[src_bel.tile].type;
+                    delta_type_bel_pin.type_bel_pin.bel_index = src_bel.index;
+                    delta_type_bel_pin.type_bel_pin.bel_pin = bel_pin.pin;
+                    srcs.emplace(delta_type_bel_pin);
+                }
+            }
+        }
+    }
+
+    TileTypeBelPin type_bel_pin;
+    type_bel_pin.tile_type = ctx->chip_info->tiles[bel.tile].type;
+    type_bel_pin.bel_index = bel.index;
+    type_bel_pin.bel_pin = pin;
+
+    auto result = pins_with_dedicate_interconnect.emplace(type_bel_pin, srcs);
+    if(!result.second) {
+        // type_bel_pin was already present! Add any new sources from this
+        // sink type (if any);
+        for(auto src : srcs) {
+            result.first->second.emplace(src);
+        }
+    }
+}
+
+NEXTPNR_NAMESPACE_END
diff --git a/fpga_interchange/dedicated_interconnect.h b/fpga_interchange/dedicated_interconnect.h
new file mode 100644
index 00000000..5fe61d30
--- /dev/null
+++ b/fpga_interchange/dedicated_interconnect.h
@@ -0,0 +1,129 @@
+/*
+ *  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.
+ *
+ */
+
+#ifndef NEXTPNR_H
+#error Include "dedicated_interconnect.h" via "nextpnr.h" only.
+#endif
+
+NEXTPNR_NAMESPACE_BEGIN
+
+struct TileTypeBelPin {
+    int32_t tile_type;
+    int32_t bel_index;
+    IdString bel_pin;
+
+    bool operator < (const TileTypeBelPin &other) const {
+        if(tile_type >= other.tile_type) {
+            return false;
+        }
+
+        if(bel_index >= other.bel_index) {
+            return false;
+        }
+
+        return bel_pin < other.bel_pin;
+    }
+
+    bool operator ==(const TileTypeBelPin &other) const {
+        return tile_type == other.tile_type && bel_index == other.bel_index && bel_pin == other.bel_pin;
+    }
+    bool operator !=(const TileTypeBelPin &other) const {
+        return tile_type != other.tile_type || bel_index != other.bel_index || bel_pin != other.bel_pin;
+    }
+};
+
+struct DeltaTileTypeBelPin {
+    int32_t delta_x;
+    int32_t delta_y;
+    TileTypeBelPin type_bel_pin;
+
+    bool operator ==(const DeltaTileTypeBelPin &other) const {
+        return delta_x == other.delta_x && delta_y == other.delta_y && type_bel_pin == other.type_bel_pin;
+    }
+    bool operator !=(const DeltaTileTypeBelPin &other) const {
+        return delta_x != other.delta_x || delta_y != other.delta_y || type_bel_pin != other.type_bel_pin;
+    }
+};
+
+NEXTPNR_NAMESPACE_END
+
+template <> struct std::hash<NEXTPNR_NAMESPACE_PREFIX TileTypeBelPin>
+{
+    std::size_t operator()(const NEXTPNR_NAMESPACE_PREFIX TileTypeBelPin &type_bel_pin) const noexcept
+    {
+        std::size_t seed = 0;
+        boost::hash_combine(seed, std::hash<int32_t>()(type_bel_pin.tile_type));
+        boost::hash_combine(seed, std::hash<int32_t>()(type_bel_pin.bel_index));
+        boost::hash_combine(seed, std::hash<NEXTPNR_NAMESPACE_PREFIX IdString>()(type_bel_pin.bel_pin));
+        return seed;
+    }
+};
+
+template <> struct std::hash<NEXTPNR_NAMESPACE_PREFIX DeltaTileTypeBelPin>
+{
+    std::size_t operator()(const NEXTPNR_NAMESPACE_PREFIX DeltaTileTypeBelPin &delta_bel_pin) const noexcept
+    {
+        std::size_t seed = 0;
+        boost::hash_combine(seed, std::hash<int32_t>()(delta_bel_pin.delta_x));
+        boost::hash_combine(seed, std::hash<int32_t>()(delta_bel_pin.delta_y));
+        boost::hash_combine(seed, std::hash<NEXTPNR_NAMESPACE_PREFIX TileTypeBelPin>()(delta_bel_pin.type_bel_pin));
+        return seed;
+    }
+};
+
+NEXTPNR_NAMESPACE_BEGIN
+
+struct Context;
+
+// This class models dedicated interconnect present in the given fabric.
+//
+// Examples of dedicate interconnect:
+//  - IBUF.O -> ISERDES.I
+//  - IBUF.O -> IDELAY.I
+//  - CARRY4.CO[3] -> CARRY4.CIN
+//
+//  Note that CARRY4.CYINIT does not **require** dedicated interconnect, so
+//  it doesn't qualify.
+//
+//  This class discovers dedicated interconnect by examing the routing graph.
+//  This discovery make be expensive, and require caching to accelerate
+//  startup.
+struct DedicatedInterconnect {
+    const Context *ctx;
+
+    std::unordered_map<TileTypeBelPin, std::unordered_set<DeltaTileTypeBelPin>> pins_with_dedicate_interconnect;
+
+    void init(const Context *ctx);
+
+    // Is this BEL placed in a location that is valid based on dedicated
+    // interconnect?
+    //
+    // Note: Only BEL pin sinks are checked.
+    bool isBelLocationValid(BelId bel, const CellInfo* cell) const;
+
+    void find_dedicated_interconnect();
+    void print_dedicated_interconnect() const;
+    bool check_routing(
+        BelId src_bel, IdString src_bel_pin,
+        BelId dst_bel, IdString dst_bel_pin) const;
+    void expand_bel(BelId bel, IdString pin, WireId wire);
+};
+
+NEXTPNR_NAMESPACE_END
diff --git a/fpga_interchange/examples/ff/Makefile b/fpga_interchange/examples/ff/Makefile
new file mode 100644
index 00000000..c6118ff7
--- /dev/null
+++ b/fpga_interchange/examples/ff/Makefile
@@ -0,0 +1,8 @@
+DESIGN := ff
+DESIGN_TOP := top
+PACKAGE := csg324
+
+include ../template.mk
+
+build/ff.json: ff.v | build
+	yosys -c run.tcl
diff --git a/fpga_interchange/examples/ff/ff.v b/fpga_interchange/examples/ff/ff.v
new file mode 100644
index 00000000..1c271042
--- /dev/null
+++ b/fpga_interchange/examples/ff/ff.v
@@ -0,0 +1,11 @@
+module top(input clk, input d, input r, output reg q);
+
+always @(posedge clk)
+begin
+    if(r)
+        q <= 1'b0;
+    else
+        q <= d;
+end
+
+endmodule
diff --git a/fpga_interchange/examples/ff/ff.xdc b/fpga_interchange/examples/ff/ff.xdc
new file mode 100644
index 00000000..3c132f1d
--- /dev/null
+++ b/fpga_interchange/examples/ff/ff.xdc
@@ -0,0 +1,9 @@
+set_property PACKAGE_PIN P17 [get_ports clk]
+set_property PACKAGE_PIN N15 [get_ports d]
+set_property PACKAGE_PIN N16 [get_ports r]
+set_property PACKAGE_PIN M17 [get_ports q]
+
+set_property IOSTANDARD LVCMOS33 [get_ports clk]
+set_property IOSTANDARD LVCMOS33 [get_ports d]
+set_property IOSTANDARD LVCMOS33 [get_ports r]
+set_property IOSTANDARD LVCMOS33 [get_ports q]
diff --git a/fpga_interchange/examples/ff/run.tcl b/fpga_interchange/examples/ff/run.tcl
new file mode 100644
index 00000000..726d86eb
--- /dev/null
+++ b/fpga_interchange/examples/ff/run.tcl
@@ -0,0 +1,14 @@
+yosys -import
+
+read_verilog ff.v
+
+synth_xilinx -nolutram -nowidelut -nosrl -nocarry -nodsp
+
+# opt_expr -undriven makes sure all nets are driven, if only by the $undef
+# net.
+opt_expr -undriven
+opt_clean
+
+setundef -zero -params
+
+write_json build/ff.json
diff --git a/fpga_interchange/fpga_interchange.cpp b/fpga_interchange/fpga_interchange.cpp
index ad1dd76d..fd57e09c 100644
--- a/fpga_interchange/fpga_interchange.cpp
+++ b/fpga_interchange/fpga_interchange.cpp
@@ -311,9 +311,6 @@ void FpgaInterchange::write_physical_netlist(const Context * ctx, const std::str
     for(auto & cell_name : placed_cells) {
         const CellInfo & cell = *ctx->cells.at(cell_name);
 
-        if(ctx->io_port_types.count(cell.type)) {
-            continue;
-        }
         if(ctx->is_bel_synthetic(cell.bel)) {
             continue;
         }
@@ -321,15 +318,14 @@ void FpgaInterchange::write_physical_netlist(const Context * ctx, const std::str
         number_placements += 1;
     }
 
+    std::vector<IdString> ports;
+
     std::unordered_map<std::string, std::string> sites;
     auto placements = phys_netlist.initPlacements(number_placements);
     auto placement_iter = placements.begin();
 
     for(auto & cell_name : placed_cells) {
         const CellInfo & cell = *ctx->cells.at(cell_name);
-        if(ctx->io_port_types.count(cell.type)) {
-            continue;
-        }
         if(ctx->is_bel_synthetic(cell.bel)) {
             continue;
         }
@@ -351,7 +347,13 @@ void FpgaInterchange::write_physical_netlist(const Context * ctx, const std::str
         auto placement = *placement_iter++;
 
         placement.setCellName(strings.get_index(cell.name.str(ctx)));
-        placement.setType(strings.get_index(cell.type.str(ctx)));
+        if(ctx->io_port_types.count(cell.type)) {
+            // Always mark IO ports as type <PORT>.
+            placement.setType(strings.get_index("<PORT>"));
+            ports.push_back(cell.name);
+        } else {
+            placement.setType(strings.get_index(cell.type.str(ctx)));
+        }
         placement.setSite(strings.get_index(site_name));
 
         size_t bel_index = strings.get_index(bel_name[1].str(ctx));
@@ -359,27 +361,38 @@ void FpgaInterchange::write_physical_netlist(const Context * ctx, const std::str
         placement.setIsBelFixed(cell.belStrength >= STRENGTH_FIXED);
         placement.setIsSiteFixed(cell.belStrength >= STRENGTH_FIXED);
 
-        size_t pin_count = 0;
-        for(const auto & pin : cell.cell_bel_pins) {
-            pin_count += pin.second.size();
-        }
+        if(!ctx->io_port_types.count(cell.type)) {
+            // Don't emit pin map for ports.
+            size_t pin_count = 0;
+            for(const auto & pin : cell.cell_bel_pins) {
+                pin_count += pin.second.size();
+            }
 
-        auto pins = placement.initPinMap(pin_count);
-        auto pin_iter = pins.begin();
+            auto pins = placement.initPinMap(pin_count);
+            auto pin_iter = pins.begin();
 
-        for(const auto & cell_to_bel_pins : cell.cell_bel_pins) {
-            std::string cell_pin = cell_to_bel_pins.first.str(ctx);
-            size_t cell_pin_index = strings.get_index(cell_pin);
+            for(const auto & cell_to_bel_pins : cell.cell_bel_pins) {
+                std::string cell_pin = cell_to_bel_pins.first.str(ctx);
+                size_t cell_pin_index = strings.get_index(cell_pin);
 
-            for(const auto & bel_pin : cell_to_bel_pins.second) {
-                auto pin_output = *pin_iter++;
-                pin_output.setCellPin(cell_pin_index);
-                pin_output.setBel(bel_index);
-                pin_output.setBelPin(strings.get_index(bel_pin.str(ctx)));
+                for(const auto & bel_pin : cell_to_bel_pins.second) {
+                    auto pin_output = *pin_iter++;
+                    pin_output.setCellPin(cell_pin_index);
+                    pin_output.setBel(bel_index);
+                    pin_output.setBelPin(strings.get_index(bel_pin.str(ctx)));
+                }
             }
         }
     }
 
+    auto phys_cells = phys_netlist.initPhysCells(ports.size());
+    auto phys_cells_iter = phys_cells.begin();
+    for(IdString port : ports) {
+        auto phys_cell = *phys_cells_iter++;
+        phys_cell.setCellName(strings.get_index(port.str(ctx)));
+        phys_cell.setPhysType(PhysicalNetlist::PhysNetlist::PhysCellType::PORT);
+    }
+
     auto nets = phys_netlist.initPhysNets(ctx->nets.size());
     auto net_iter = nets.begin();
     for(auto & net_pair : ctx->nets) {
diff --git a/fpga_interchange/main.cc b/fpga_interchange/main.cc
index 5a49cbdc..958f1d95 100644
--- a/fpga_interchange/main.cc
+++ b/fpga_interchange/main.cc
@@ -70,6 +70,7 @@ void FpgaInterchangeCommandHandler::customBitstream(Context *ctx)
 std::unique_ptr<Context> FpgaInterchangeCommandHandler::createContext(std::unordered_map<std::string, Property> &values)
 {
     auto start = std::chrono::high_resolution_clock::now();
+
     ArchArgs chipArgs;
     if (!vm.count("chipdb")) {
         log_error("chip database binary must be provided\n");
@@ -81,6 +82,16 @@ std::unique_ptr<Context> FpgaInterchangeCommandHandler::createContext(std::unord
 
     auto ctx = std::unique_ptr<Context>(new Context(chipArgs));
 
+    if (vm.count("verbose")) {
+        ctx->verbose = true;
+    }
+    if (vm.count("debug")) {
+        ctx->verbose = true;
+        ctx->debug = true;
+    }
+
+    ctx->init();
+
     if (vm.count("netlist")) {
         ctx->read_logical_netlist(vm["netlist"].as<std::string>());
     }
diff --git a/fpga_interchange/site_router.cc b/fpga_interchange/site_router.cc
index 09e01507..a22dfcd3 100644
--- a/fpga_interchange/site_router.cc
+++ b/fpga_interchange/site_router.cc
@@ -260,6 +260,12 @@ struct SiteInformation
             if (!result.second && result.first->second != net) {
                 // Conflict, this wire is already in use and it's not
                 // doesn't match!
+                if(verbose_site_router(ctx)) {
+                    log_info("Cannot select route because net %s != net %s\n",
+                            result.first->second->name.c_str(ctx),
+                            net->name.c_str(ctx));
+                }
+
                 return false;
             }