Merge pull request #694 from YosysHQ/gatecat/interchange-glbroute

interchange: Initial global routing implementation

.github/workflows/interchange_ci.yml

@@ -108,7 +108,7 @@ jobs:
       env:
         RAPIDWRIGHT_PATH: ${{ github.workspace }}/RapidWright
         PYTHON_INTERCHANGE_PATH: ${{ github.workspace }}/python-fpga-interchange
-        PYTHON_INTERCHANGE_TAG: v0.0.11
+        PYTHON_INTERCHANGE_TAG: v0.0.12
         PRJOXIDE_REVISION: b5d88c3491770559c3c10cccb1651db65ab061b1
         DEVICE: ${{ matrix.device }}
       run: |

fpga_interchange/arch.cc

@@ -479,6 +479,32 @@ IdString Arch::getWireType(WireId wire) const
     return IdString(chip_info->wire_types[wire_type].name);
 }
 
+bool Arch::is_site_wire(WireId wire) const
+{
+    if (wire.tile == -1)
+        return false;
+    const auto &tile_type = loc_info(chip_info, wire);
+    return tile_type.wire_data[wire.index].site != -1;
+}
+
+WireCategory Arch::get_wire_category(WireId wire) const
+{
+    int tile = wire.tile, index = wire.index;
+    if (tile == -1) {
+        // Nodal wire
+        const TileWireRefPOD &wr = chip_info->nodes[wire.index].tile_wires[0];
+        tile = wr.tile;
+        index = wr.index;
+    }
+    auto &w2t = chip_info->tiles[tile].tile_wire_to_type;
+    if (index >= w2t.ssize())
+        return WIRE_CAT_GENERAL;
+    int wire_type = w2t[index];
+    if (wire_type == -1)
+        return WIRE_CAT_GENERAL;
+    return WireCategory(chip_info->wire_types[wire_type].category);
+}
+
 std::vector<std::pair<IdString, std::string>> Arch::getWireAttrs(WireId wire) const { return {}; }
 
 // -----------------------------------------------------------------------
@@ -773,6 +799,8 @@ bool Arch::place()
     getCtx()->check();
 #endif
 
+    place_globals();
+
     std::string placer = str_or_default(settings, id("placer"), defaultPlacer);
     if (placer == "heap") {
         PlacerHeapCfg cfg(getCtx());
@@ -895,6 +923,8 @@ bool Arch::route()
     // terminate at a BEL pin.
     disallow_site_routing = true;
 
+    route_globals();
+
     bool result;
     if (router == "router1") {
         result = router1(getCtx(), Router1Cfg(getCtx()));

fpga_interchange/arch.h

@@ -533,6 +533,9 @@ struct Arch : ArchAPI<ArchRanges>
         return range;
     }
 
+    bool is_site_wire(WireId wire) const;
+    WireCategory get_wire_category(WireId wire) const;
+
     // -------------------------------------------------
 
     PipId getPipByName(IdStringList name) const final;
@@ -686,6 +689,11 @@ struct Arch : ArchAPI<ArchRanges>
                       std::unordered_set<CellInfo *> *placed_cells);
     void pack_ports();
     void decode_lut_cells();
+
+    const GlobalCellPOD *global_cell_info(IdString cell_type) const;
+    void place_globals();
+    void route_globals();
+
     bool pack() final;
     bool place() final;
     bool route() final;

fpga_interchange/chipdb.h

@@ -34,7 +34,7 @@ NEXTPNR_NAMESPACE_BEGIN
  * kExpectedChipInfoVersion
  */
 
-static constexpr int32_t kExpectedChipInfoVersion = 8;
+static constexpr int32_t kExpectedChipInfoVersion = 9;
 
 // Flattened site indexing.
 //
@@ -320,6 +320,18 @@ NPNR_PACKED_STRUCT(struct WireTypePOD {
     int32_t category; // WireCategory
 });
 
+NPNR_PACKED_STRUCT(struct GlobalCellPinPOD {
+    int32_t name;     // constid
+    int16_t max_hops; // max routing hops to try
+    int8_t guide_placement;
+    int8_t force_routing;
+});
+
+NPNR_PACKED_STRUCT(struct GlobalCellPOD {
+    int32_t cell_type;
+    RelSlice<GlobalCellPinPOD> pins;
+});
+
 NPNR_PACKED_STRUCT(struct ChipInfoPOD {
     RelPtr<char> name;
     RelPtr<char> generator;
@@ -333,6 +345,7 @@ NPNR_PACKED_STRUCT(struct ChipInfoPOD {
     RelSlice<NodeInfoPOD> nodes;
     RelSlice<PackagePOD> packages;
     RelSlice<WireTypePOD> wire_types;
+    RelSlice<GlobalCellPOD> global_cells;
 
     // BEL bucket constids.
     RelSlice<int32_t> bel_buckets;

fpga_interchange/globals.cc

@@ -0,0 +1,284 @@
+/*
+ *  nextpnr -- Next Generation Place and Route
+ *
+ *  Copyright (C) 2021  gatecat <gatecat@ds0.me>
+ *
+ *  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 "log.h"
+#include "nextpnr.h"
+#include "util.h"
+
+#include <queue>
+
+NEXTPNR_NAMESPACE_BEGIN
+
+namespace {
+
+struct GlobalVist
+{
+    PipId downhill = PipId();
+    int total_hops = 0;
+    int global_hops = 0;
+    bool operator<(const GlobalVist &other) const
+    {
+        return (total_hops < other.total_hops) ||
+               ((total_hops == other.total_hops) && (global_hops > other.global_hops));
+    }
+};
+
+// This is our main global routing implementation. It is used both to actually route globals; and also to discover if
+// global buffers have available short routes from their source for auto-placement
+static int route_global_arc(Context *ctx, NetInfo *net, size_t usr_idx, size_t phys_port_idx, int max_hops,
+                            bool dry_run)
+{
+    auto &usr = net->users.at(usr_idx);
+    WireId src = ctx->getNetinfoSourceWire(net);
+    WireId dest = ctx->getNetinfoSinkWire(net, usr, phys_port_idx);
+    if (dest == WireId()) {
+        if (dry_run)
+            return -1;
+        else
+            log_error("Arc %d.%d (%s.%s) of net %s has no sink wire!\n", int(usr_idx), int(phys_port_idx),
+                      ctx->nameOf(usr.cell), ctx->nameOf(usr.port), ctx->nameOf(net));
+    }
+    // Consider any existing routing put in place by the site router, etc
+    int start_hops = 0;
+    while (net->wires.count(dest) && dest != src) {
+        dest = ctx->getPipSrcWire(net->wires.at(dest).pip);
+        ++start_hops;
+    }
+    // The main BFS implementation
+    // Currently this is a backwards-BFS from sink to source (or pre-existing routing) that avoids general routing. It
+    // currently aims for minimum hops as a primary goal and maximum global resource usage as a secondary goal. More
+    // advanced heuristics will likely be needed for more complex situation
+    WireId startpoint;
+    GlobalVist best_visit;
+    std::queue<WireId> visit_queue;
+    std::unordered_map<WireId, GlobalVist> visits;
+
+    visit_queue.push(dest);
+    visits[dest].downhill = PipId();
+    visits[dest].total_hops = start_hops;
+
+    while (!visit_queue.empty()) {
+        WireId cursor = visit_queue.front();
+        visit_queue.pop();
+        auto &curr_visit = visits.at(cursor);
+        // We're now at least one layer deeper than a valid visit, any further exploration is futile
+        if (startpoint != WireId() && curr_visit.total_hops > best_visit.total_hops)
+            break;
+        // Valid end of routing
+        if ((cursor == src) || (ctx->getBoundWireNet(cursor) == net)) {
+            if (startpoint == WireId() || curr_visit < best_visit) {
+                startpoint = cursor;
+                best_visit = curr_visit;
+            }
+        }
+        // Explore uphill
+        for (auto pip : ctx->getPipsUphill(cursor)) {
+            if (!dry_run && !ctx->checkPipAvailForNet(pip, net))
+                continue;
+            WireId pip_src = ctx->getPipSrcWire(pip);
+            if (!dry_run && !ctx->checkWireAvail(pip_src) && ctx->getBoundWireNet(pip_src) != net)
+                continue;
+            auto cat = ctx->get_wire_category(pip_src);
+            if (!ctx->is_site_wire(pip_src) && cat == WIRE_CAT_GENERAL)
+                continue; // never allow general routing
+            GlobalVist next_visit;
+            next_visit.downhill = pip;
+            next_visit.total_hops = curr_visit.total_hops + 1;
+            if (max_hops != -1 && next_visit.total_hops > max_hops)
+                continue;
+            next_visit.global_hops = curr_visit.global_hops + ((cat == WIRE_CAT_GLOBAL) ? 1 : 0);
+            auto fnd_src = visits.find(pip_src);
+            if (fnd_src == visits.end() || next_visit < fnd_src->second) {
+                visit_queue.push(pip_src);
+                visits[pip_src] = next_visit;
+            }
+        }
+    }
+
+    if (startpoint == WireId())
+        return -1;
+    if (!dry_run) {
+        if (ctx->getBoundWireNet(startpoint) == nullptr)
+            ctx->bindWire(startpoint, net, STRENGTH_LOCKED);
+
+        WireId cursor = startpoint;
+        std::vector<PipId> pips;
+        // Create a list of pips on the routed path
+        while (true) {
+            PipId pip = visits.at(cursor).downhill;
+            if (pip == PipId())
+                break;
+            pips.push_back(pip);
+            cursor = ctx->getPipDstWire(pip);
+        }
+        // Reverse that list
+        std::reverse(pips.begin(), pips.end());
+        // Bind pips until we hit already-bound routing
+        for (PipId pip : pips) {
+            WireId dst = ctx->getPipDstWire(pip);
+            if (ctx->getBoundWireNet(dst) == net)
+                break;
+            ctx->bindPip(pip, net, STRENGTH_LOCKED);
+        }
+    }
+    return visits.at(startpoint).total_hops;
+}
+}; // namespace
+
+const GlobalCellPOD *Arch::global_cell_info(IdString cell_type) const
+{
+    for (const auto &glb_cell : chip_info->global_cells)
+        if (IdString(glb_cell.cell_type) == cell_type)
+            return &glb_cell;
+
+    return nullptr;
+}
+
+void Arch::place_globals()
+{
+    log_info("Placing globals...\n");
+
+    Context *ctx = getCtx();
+    IdString gnd_net_name(chip_info->constants->gnd_net_name);
+    IdString vcc_net_name(chip_info->constants->vcc_net_name);
+
+    // TODO: for more complex PLL type setups, we might want a toposort or iterative loop as the PLL must be placed
+    // before the GBs it drives
+    for (auto cell : sorted(ctx->cells)) {
+        CellInfo *ci = cell.second;
+        const GlobalCellPOD *glb_cell = global_cell_info(ci->type);
+        if (glb_cell == nullptr)
+            continue;
+        // Ignore if already placed
+        if (ci->bel != BelId())
+            continue;
+
+        for (const auto &pin : glb_cell->pins) {
+            if (!pin.guide_placement)
+                continue;
+
+            IdString pin_name(pin.name);
+            if (!ci->ports.count(pin_name))
+                continue;
+            auto &port = ci->ports.at(pin_name);
+
+            // only input ports currently used for placement guidance
+            if (port.type != PORT_IN)
+                continue;
+
+            NetInfo *net = port.net;
+            if (net == nullptr || net->name == gnd_net_name || net->name == vcc_net_name)
+                continue;
+            // Ignore if there is no driver; or the driver is not placed
+            if (net->driver.cell == nullptr || net->driver.cell->bel == BelId())
+                continue;
+            size_t user_idx = 0;
+            bool found_user = false;
+            for (user_idx = 0; user_idx < net->users.size(); user_idx++)
+                if (net->users.at(user_idx).cell == ci && net->users.at(user_idx).port == pin_name) {
+                    found_user = true;
+                    break;
+                }
+            NPNR_ASSERT(found_user);
+
+            // TODO: substantial performance improvements are probably possible, although of questionable benefit given
+            // the low number of globals in a typical device...
+            BelId best_bel;
+            int shortest_distance = std::numeric_limits<int>::max();
+
+            for (auto bel : getBels()) {
+                int distance;
+                if (!isValidBelForCellType(ci->type, bel))
+                    continue;
+                if (!checkBelAvail(bel))
+                    continue;
+                // Provisionally place
+                bindBel(bel, ci, STRENGTH_WEAK);
+                if (!isBelLocationValid(bel))
+                    goto fail;
+                // Check distance
+                distance = route_global_arc(ctx, net, user_idx, 0, pin.max_hops, true);
+                if (distance != -1 && distance < shortest_distance) {
+                    best_bel = bel;
+                    shortest_distance = distance;
+                }
+            fail:
+                unbindBel(bel);
+            }
+
+            if (best_bel != BelId()) {
+                bindBel(best_bel, ci, STRENGTH_LOCKED);
+                log_info("    placed %s:%s at %s\n", ctx->nameOf(ci), ctx->nameOf(ci->type), ctx->nameOfBel(best_bel));
+                break;
+            }
+        }
+    }
+}
+
+void Arch::route_globals()
+{
+    log_info("Routing globals...\n");
+
+    Context *ctx = getCtx();
+    IdString gnd_net_name(chip_info->constants->gnd_net_name);
+    IdString vcc_net_name(chip_info->constants->vcc_net_name);
+
+    for (auto cell : sorted(ctx->cells)) {
+        CellInfo *ci = cell.second;
+        const GlobalCellPOD *glb_cell = global_cell_info(ci->type);
+        if (glb_cell == nullptr)
+            continue;
+        for (const auto &pin : glb_cell->pins) {
+            IdString pin_name(pin.name);
+            if (!ci->ports.count(pin_name))
+                continue;
+            auto &port = ci->ports.at(pin_name);
+
+            // TOOD: routing of input ports, too
+            // output ports are generally the first priority though
+            if (port.type != PORT_OUT)
+                continue;
+
+            NetInfo *net = port.net;
+            if (net == nullptr || net->name == gnd_net_name || net->name == vcc_net_name)
+                continue;
+
+            int total_sinks = 0;
+            int global_sinks = 0;
+
+            for (size_t i = 0; i < net->users.size(); i++) {
+                auto &usr = net->users.at(i);
+                for (size_t j = 0; j < ctx->getNetinfoSinkWireCount(net, usr); j++) {
+                    int result = route_global_arc(ctx, net, i, j, pin.max_hops, false);
+                    ++total_sinks;
+                    if (result != -1)
+                        ++global_sinks;
+                    if ((result == -1) && pin.force_routing)
+                        log_error("Failed to route arc %d.%d (%s.%s) of net %s using dedicated global routing!\n",
+                                  int(i), int(j), ctx->nameOf(usr.cell), ctx->nameOf(usr.port), ctx->nameOf(net));
+                }
+            }
+
+            log_info("    routed %d/%d sinks of net %s using dedicated routing.\n", global_sinks, total_sinks,
+                     ctx->nameOf(net));
+        }
+    }
+}
+
+NEXTPNR_NAMESPACE_END