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+/*
+ *  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.
+ *
+ */
+
+#ifndef VIADUCT_API_H
+#define VIADUCT_API_H
+
+#include "nextpnr_namespaces.h"
+#include "nextpnr_types.h"
+
+NEXTPNR_NAMESPACE_BEGIN
+
+/*
+Viaduct -- a series of small arches
+
+Viaduct is a framework that provides an 'inbetween' step between nextpnr-generic
+using Python bindings and a full-custom arch.
+
+It allows an arch to programmatically build a set of bels (placement locations)
+and a routing graph in-memory at startup; and then hook into nextpnr's flow
+and validity checking rules at runtime with custom C++ code.
+
+To create a Viaduct 'uarch', the following are required:
+ - an implementation of ViaductAPI. At a minimum; you will need to use ctx->addBel, ctx->addWire and ctx->addPip to
+create the graph of placement and routing resources in-memory. Also implement any placement validity checking required -
+like rules for how LUTs and FFs can be placed together in a SLICE.
+ - an instance of a struct deriving from ViaductArch - this is how the uarch is discovered. Override create(args) to
+create an instance of your ViaductAPI implementation.
+ - these should be within C++ files in a new subfolder of 'viaduct'. Add the name of this subfolder to the list of
+VIADUCT_UARCHES in family.cmake if building in-tree.
+
+For an example of how these pieces fit together; see 'viaduct/example' which implements a small synthetic architecture
+using this framework.
+
+*/
+
+struct Context;
+
+struct ViaductAPI
+{
+    virtual void init(Context *ctx);
+    Context *ctx;
+
+    // --- Bel functions ---
+    // Called when a bel is placed/unplaced (with cell=nullptr for a unbind)
+    virtual void notifyBelChange(BelId bel, CellInfo *cell) {}
+    // This only needs to return false if a bel is disabled for a microarch-specific reason and not just because it's
+    // bound (which the base generic will deal with)
+    virtual bool checkBelAvail(BelId bel) const { return true; }
+    // Mirror the ArchAPI functions - see archapi.md
+    virtual std::vector<IdString> getCellTypes() const;
+    virtual BelBucketId getBelBucketForBel(BelId bel) const;
+    virtual BelBucketId getBelBucketForCellType(IdString cell_type) const;
+    virtual bool isValidBelForCellType(IdString cell_type, BelId bel) const;
+    virtual bool isBelLocationValid(BelId bel) const { return true; }
+
+    // --- Wire and pip functions ---
+    // Called when a wire/pip is placed/unplaced (with net=nullptr for a unbind)
+    virtual void notifyWireChange(WireId wire, NetInfo *net) {}
+    virtual void notifyPipChange(PipId pip, NetInfo *net) {}
+    // These only need to return false if a wire/pip is disabled for a microarch-specific reason and not just because
+    // it's bound (which the base arch will deal with)
+    virtual bool checkWireAvail(WireId wire) const { return true; }
+    virtual bool checkPipAvail(PipId pip) const { return true; }
+    virtual bool checkPipAvailForNet(PipId pip, NetInfo *net) const { return checkPipAvail(pip); };
+
+    // --- Route lookahead ---
+    virtual delay_t estimateDelay(WireId src, WireId dst) const;
+    virtual delay_t predictDelay(BelId src_bel, IdString src_pin, BelId dst_bel, IdString dst_pin) const;
+    virtual ArcBounds getRouteBoundingBox(WireId src, WireId dst) const;
+
+    // --- Flow hooks ---
+    virtual void pack(){}; // replaces the pack function
+    // Called before and after main placement and routing
+    virtual void prePlace(){};
+    virtual void postPlace(){};
+    virtual void preRoute(){};
+    virtual void postRoute(){};
+
+    virtual ~ViaductAPI(){};
+};
+
+struct ViaductArch
+{
+    static ViaductArch *list_head;
+    ViaductArch *list_next = nullptr;
+
+    std::string name;
+    ViaductArch(const std::string &name);
+    ~ViaductArch(){};
+    virtual std::unique_ptr<ViaductAPI> create(const dict<std::string, std::string> &args) = 0;
+
+    static std::string list();
+    static std::unique_ptr<ViaductAPI> create(const std::string &name, const dict<std::string, std::string> &args);
+};
+
+NEXTPNR_NAMESPACE_END
+
+#endif