Move json parser from frontend/json/ to json/

Signed-off-by: Clifford Wolf <clifford@clifford.at>

2 files changed, 811 insertions, 0 deletions

diff --git a/json/jsonparse.cc b/json/jsonparse.cc
new file mode 100644
index 00000000..463efdd2
--- /dev/null
+++ b/json/jsonparse.cc
@@ -0,0 +1,778 @@
+/*
+ *  nextpnr -- Next Generation Place and Route
+ *
+ *  Copyright (C) 2018  SymbioticEDA
+ *
+ *  jsonparse.cc -- liberally copied from the yosys file of the same name by
+ *
+ *  Copyright (C) 2018  Clifford Wolf <clifford@symbioticeda.com>
+ *
+ *  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 "jsonparse.h"
+#include <assert.h>
+#include <fstream>
+#include <iostream>
+#include <log.h>
+#include <map>
+#include <string>
+#include "nextpnr.h"
+
+NEXTPNR_NAMESPACE_BEGIN
+
+extern bool check_all_nets_driven(Context *ctx);
+
+namespace JsonParser {
+
+const bool json_debug = false;
+
+typedef std::string string;
+
+template <typename T> int GetSize(const T &obj) { return obj.size(); }
+
+struct JsonNode
+{
+    char type; // S=String, N=Number, A=Array, D=Dict
+    string data_string;
+    int data_number;
+    std::vector<JsonNode *> data_array;
+    std::map<string, JsonNode *> data_dict;
+    std::vector<string> data_dict_keys;
+
+    JsonNode(std::istream &f)
+    {
+        type = 0;
+        data_number = 0;
+
+        while (1) {
+            int ch = f.get();
+
+            if (ch == EOF)
+                log_error("Unexpected EOF in JSON file.\n");
+
+            if (ch == ' ' || ch == '\t' || ch == '\r' || ch == '\n')
+                continue;
+
+            if (ch == '\"') {
+                type = 'S';
+
+                while (1) {
+                    ch = f.get();
+
+                    if (ch == EOF)
+                        log_error("Unexpected EOF in JSON string.\n");
+
+                    if (ch == '\"')
+                        break;
+
+                    if (ch == '\\') {
+                        int ch = f.get();
+
+                        if (ch == EOF)
+                            log_error("Unexpected EOF in JSON string.\n");
+                    }
+
+                    data_string += ch;
+                }
+
+                break;
+            }
+
+            if ('0' <= ch && ch <= '9') {
+                type = 'N';
+                data_number = ch - '0';
+                data_string += ch;
+
+                while (1) {
+                    ch = f.get();
+
+                    if (ch == EOF)
+                        break;
+
+                    if (ch == '.')
+                        goto parse_real;
+
+                    if (ch < '0' || '9' < ch) {
+                        f.unget();
+                        break;
+                    }
+
+                    data_number = data_number * 10 + (ch - '0');
+                    data_string += ch;
+                }
+
+                data_string = "";
+                break;
+
+            parse_real:
+                type = 'S';
+                data_number = 0;
+                data_string += ch;
+
+                while (1) {
+                    ch = f.get();
+
+                    if (ch == EOF)
+                        break;
+
+                    if (ch < '0' || '9' < ch) {
+                        f.unget();
+                        break;
+                    }
+
+                    data_string += ch;
+                }
+
+                break;
+            }
+
+            if (ch == '[') {
+                type = 'A';
+
+                while (1) {
+                    ch = f.get();
+
+                    if (ch == EOF)
+                        log_error("Unexpected EOF in JSON file.\n");
+
+                    if (ch == ' ' || ch == '\t' || ch == '\r' || ch == '\n' || ch == ',')
+                        continue;
+
+                    if (ch == ']')
+                        break;
+
+                    f.unget();
+                    data_array.push_back(new JsonNode(f));
+                }
+
+                break;
+            }
+
+            if (ch == '{') {
+                type = 'D';
+
+                while (1) {
+                    ch = f.get();
+
+                    if (ch == EOF)
+                        log_error("Unexpected EOF in JSON file.\n");
+
+                    if (ch == ' ' || ch == '\t' || ch == '\r' || ch == '\n' || ch == ',')
+                        continue;
+
+                    if (ch == '}')
+                        break;
+
+                    f.unget();
+                    JsonNode key(f);
+
+                    while (1) {
+                        ch = f.get();
+
+                        if (ch == EOF)
+                            log_error("Unexpected EOF in JSON file.\n");
+
+                        if (ch == ' ' || ch == '\t' || ch == '\r' || ch == '\n' || ch == ':')
+                            continue;
+
+                        f.unget();
+                        break;
+                    }
+
+                    JsonNode *value = new JsonNode(f);
+
+                    if (key.type != 'S')
+                        log_error("Unexpected non-string key in JSON dict.\n");
+
+                    data_dict[key.data_string] = value;
+                    data_dict_keys.push_back(key.data_string);
+                }
+
+                break;
+            }
+
+            log_error("Unexpected character in JSON file: '%c'\n", ch);
+        }
+    }
+
+    ~JsonNode()
+    {
+        for (auto it : data_array)
+            delete it;
+        for (auto &it : data_dict)
+            delete it.second;
+    }
+};
+
+NetInfo *ground_net(Context *ctx, NetInfo *net)
+{
+    CellInfo *cell = new CellInfo;
+    PortInfo port_info;
+    PortRef port_ref;
+
+    cell->name = ctx->id(net->name.str(ctx) + ".GND");
+    cell->type = ctx->id("GND");
+
+    port_info.name = ctx->id(cell->name.str(ctx) + "[]");
+    port_info.net = net;
+    port_info.type = PORT_OUT;
+
+    port_ref.cell = cell;
+    port_ref.port = port_info.name;
+
+    net->driver = port_ref;
+
+    cell->ports[port_info.name] = port_info;
+
+    return net;
+}
+
+NetInfo *vcc_net(Context *ctx, NetInfo *net)
+{
+    CellInfo *cell = new CellInfo;
+    PortInfo port_info;
+    PortRef port_ref;
+
+    cell->name = ctx->id(net->name.str(ctx) + ".VCC");
+    cell->type = ctx->id("VCC");
+
+    port_info.name = ctx->id(cell->name.str(ctx) + "[]");
+    port_info.net = net;
+    port_info.type = PORT_OUT;
+
+    port_ref.cell = cell;
+    port_ref.port = port_info.name;
+
+    net->driver = port_ref;
+
+    cell->ports[port_info.name] = port_info;
+
+    return net;
+}
+
+NetInfo *floating_net(Context *ctx, NetInfo *net)
+{
+    PortInfo port_info;
+    PortRef port_ref;
+
+    port_info.name = ctx->id(net->name.str(ctx) + ".floating");
+    port_info.net = net;
+    port_info.type = PORT_OUT;
+
+    port_ref.cell = NULL;
+    port_ref.port = port_info.name;
+
+    net->driver = port_ref;
+
+    return net;
+}
+
+//
+// is_blackbox
+//
+// Checks the JsonNode for an attributes dictionary, with a "blackbox" entry.
+// An item is deemed to be a blackbox if this entry exists and if its
+// value is not zero.  If the item is a black box, this routine will return
+// true, false otherwise
+bool is_blackbox(JsonNode *node)
+{
+    JsonNode *attr_node, *bbox_node;
+
+    if (node->data_dict.count("attributes") == 0)
+        return false;
+    attr_node = node->data_dict.at("attributes");
+    if (attr_node == NULL)
+        return false;
+    if (attr_node->type != 'D')
+        return false;
+    if (GetSize(attr_node->data_dict) == 0)
+        return false;
+    if (attr_node->data_dict.count("blackbox") == 0)
+        return false;
+    bbox_node = attr_node->data_dict.at("blackbox");
+    if (bbox_node == NULL)
+        return false;
+    if (bbox_node->type != 'N')
+        log_error("JSON module blackbox is not a number\n");
+    if (bbox_node->data_number == 0)
+        return false;
+    return true;
+}
+
+void json_import_cell_params(Context *ctx, string &modname, CellInfo *cell, JsonNode *param_node,
+                             std::unordered_map<IdString, std::string> *dest, int param_id)
+{
+    //
+    JsonNode *param;
+    IdString pId;
+    //
+    param = param_node->data_dict.at(param_node->data_dict_keys[param_id]);
+
+    pId = ctx->id(param_node->data_dict_keys[param_id]);
+    if (param->type == 'N') {
+        (*dest)[pId] = std::to_string(param->data_number);
+    } else if (param->type == 'S')
+        (*dest)[pId] = param->data_string;
+    else
+        log_error("JSON parameter type of \"%s\' of cell \'%s\' not supported\n", pId.c_str(ctx),
+                  cell->name.c_str(ctx));
+
+    if (json_debug)
+        log_info("    Added parameter \'%s\'=%s to cell \'%s\' "
+                 "of module \'%s\'\n",
+                 pId.c_str(ctx), cell->params[pId].c_str(), cell->name.c_str(ctx), modname.c_str());
+}
+
+static int const_net_idx = 0;
+
+template <typename F>
+void json_import_ports(Context *ctx, const string &modname, const std::vector<IdString> &netnames,
+                       const string &obj_name, const string &port_name, JsonNode *dir_node, JsonNode *wire_group_node,
+                       F visitor)
+{
+    // Examine a port of a cell or the design. For every bit of the port,
+    // the connected net will be processed and `visitor` will be called
+    // with (PortType dir, std::string name, NetInfo *net)
+    assert(dir_node);
+
+    if (json_debug)
+        log_info("    Examining port %s, node %s\n", port_name.c_str(), obj_name.c_str());
+
+    if (!wire_group_node)
+        log_error("JSON no connection match "
+                  "for port_direction \'%s\' of node \'%s\' "
+                  "in module \'%s\'\n",
+                  port_name.c_str(), obj_name.c_str(), modname.c_str());
+
+    assert(wire_group_node);
+
+    assert(dir_node->type == 'S');
+    assert(wire_group_node->type == 'A');
+
+    PortInfo port_info;
+
+    port_info.name = ctx->id(port_name);
+    if (dir_node->data_string.compare("input") == 0)
+        port_info.type = PORT_IN;
+    else if (dir_node->data_string.compare("output") == 0)
+        port_info.type = PORT_OUT;
+    else if (dir_node->data_string.compare("inout") == 0)
+        port_info.type = PORT_INOUT;
+    else
+        log_error("JSON unknown port direction \'%s\' in node \'%s\' "
+                  "of module \'%s\'\n",
+                  dir_node->data_string.c_str(), obj_name.c_str(), modname.c_str());
+    //
+    // Find an update, or create a net to connect
+    // to this port.
+    //
+    NetInfo *this_net = nullptr;
+    bool is_bus;
+
+    //
+    // If this port references a bus, then there will be multiple nets
+    // connected to it, all specified as part of an array.
+    //
+    is_bus = (wire_group_node->data_array.size() > 1);
+
+    // Now loop through all of the connections to this port.
+    if (wire_group_node->data_array.size() == 0) {
+        //
+        // There is/are no connections to this port.
+        //
+        // Create the port, but leave the net NULL
+
+        visitor(port_info.type, port_info.name.str(ctx), nullptr);
+
+        if (json_debug)
+            log_info("      Port \'%s\' has no connection in \'%s\'\n", port_info.name.c_str(ctx), obj_name.c_str());
+
+    } else
+        for (int index = 0; index < int(wire_group_node->data_array.size()); index++) {
+            //
+            JsonNode *wire_node;
+            PortInfo this_port;
+            IdString net_id;
+            //
+            wire_node = wire_group_node->data_array[index];
+            //
+            // Pick a name for this port
+            if (is_bus)
+                this_port.name = ctx->id(port_info.name.str(ctx) + "[" + std::to_string(index) + "]");
+            else
+                this_port.name = port_info.name;
+            this_port.type = port_info.type;
+
+            if (wire_node->type == 'N') {
+                int net_num;
+
+                // A simple net, specified by a number
+                net_num = wire_node->data_number;
+                if (net_num < int(netnames.size()))
+                    net_id = netnames.at(net_num);
+                else
+                    net_id = ctx->id(std::to_string(net_num));
+                if (ctx->nets.count(net_id) == 0) {
+                    // The net doesn't exist in the design (yet)
+                    // Create in now
+
+                    if (json_debug)
+                        log_info("      Generating a new net, \'%d\'\n", net_num);
+
+                    this_net = new NetInfo;
+                    this_net->name = net_id;
+                    this_net->driver.cell = NULL;
+                    this_net->driver.port = IdString();
+                    ctx->nets[net_id] = this_net;
+                } else {
+                    //
+                    // The net already exists within the design.
+                    // We'll connect to it
+                    //
+                    this_net = ctx->nets[net_id];
+                    if (json_debug)
+                        log_info("      Reusing net \'%s\', id \'%s\', "
+                                 "with driver \'%s\'\n",
+                                 this_net->name.c_str(ctx), net_id.c_str(ctx),
+                                 (this_net->driver.cell != NULL) ? this_net->driver.port.c_str(ctx) : "NULL");
+                }
+
+            } else if (wire_node->type == 'S') {
+                // Strings are only used to drive wires for the fixed
+                // values "0", "1", and "x".  Handle those constant
+                // values here.
+                //
+                // Constants always get their own new net
+                this_net = new NetInfo;
+                this_net->name = ctx->id("$const_" + std::to_string(const_net_idx++));
+
+                if (wire_node->data_string.compare(string("0")) == 0) {
+
+                    if (json_debug)
+                        log_info("      Generating a constant "
+                                 "zero net\n");
+                    this_net = ground_net(ctx, this_net);
+
+                } else if (wire_node->data_string.compare(string("1")) == 0) {
+
+                    if (json_debug)
+                        log_info("      Generating a constant "
+                                 "one  net\n");
+                    this_net = vcc_net(ctx, this_net);
+
+                } else if (wire_node->data_string.compare(string("x")) == 0) {
+
+                    this_net = floating_net(ctx, this_net);
+                    log_warning("      Floating wire node value, "
+                                "\'%s\' of port \'%s\' "
+                                "in cell \'%s\' of module \'%s\'\n",
+                                wire_node->data_string.c_str(), port_name.c_str(), obj_name.c_str(), modname.c_str());
+
+                } else
+                    log_error("      Unknown fixed type wire node "
+                              "value, \'%s\'\n",
+                              wire_node->data_string.c_str());
+            }
+
+            if (json_debug)
+                log_info("    Inserting port \'%s\' into cell \'%s\'\n", this_port.name.c_str(ctx), obj_name.c_str());
+            visitor(this_port.type, this_port.name.str(ctx), this_net);
+
+            if (ctx->nets.count(this_net->name) == 0)
+                ctx->nets[this_net->name] = this_net;
+        }
+}
+
+void json_import_cell(Context *ctx, string modname, const std::vector<IdString> &netnames, JsonNode *cell_node,
+                      string cell_name)
+{
+    JsonNode *cell_type, *param_node, *attr_node;
+
+    cell_type = cell_node->data_dict.at("type");
+    if (cell_type == NULL)
+        return;
+
+    CellInfo *cell = new CellInfo;
+
+    cell->name = ctx->id(cell_name);
+    assert(cell_type->type == 'S');
+    cell->type = ctx->id(cell_type->data_string);
+    // No BEL assignment here/yet
+
+    if (json_debug)
+        log_info("  Processing %s $ %s\n", modname.c_str(), cell->name.c_str(ctx));
+
+    param_node = cell_node->data_dict.at("parameters");
+    if (param_node->type != 'D')
+        log_error("JSON parameter list of \'%s\' is not a data dictionary\n", cell->name.c_str(ctx));
+
+    //
+    // Loop through all parameters, adding them into the
+    // design to annotate the cell
+    //
+    for (int paramid = 0; paramid < GetSize(param_node->data_dict_keys); paramid++) {
+
+        json_import_cell_params(ctx, modname, cell, param_node, &cell->params, paramid);
+    }
+
+    attr_node = cell_node->data_dict.at("attributes");
+    if (attr_node->type != 'D')
+        log_error("JSON attribute list of \'%s\' is not a data dictionary\n", cell->name.c_str(ctx));
+
+    //
+    // Loop through all attributes, adding them into the
+    // design to annotate the cell
+    //
+    for (int attrid = 0; attrid < GetSize(attr_node->data_dict_keys); attrid++) {
+
+        json_import_cell_params(ctx, modname, cell, attr_node, &cell->attrs, attrid);
+    }
+
+    //
+    // Now connect the ports of this module.  The ports are defined by
+    // both the port directions node as well as the connections node.
+    // Both should contain dictionaries having the same keys.
+    //
+
+    JsonNode *pdir_node = NULL;
+    if (cell_node->data_dict.count("port_directions") > 0) {
+
+        pdir_node = cell_node->data_dict.at("port_directions");
+        if (pdir_node->type != 'D')
+            log_error("JSON port_directions node of \'%s\' "
+                      "in module \'%s\' is not a "
+                      "dictionary\n",
+                      cell->name.c_str(ctx), modname.c_str());
+
+    } else if (cell_node->data_dict.count("ports") > 0) {
+        pdir_node = cell_node->data_dict.at("ports");
+        if (pdir_node->type != 'D')
+            log_error("JSON ports node of \'%s\' "
+                      "in module \'%s\' is not a "
+                      "dictionary\n",
+                      cell->name.c_str(ctx), modname.c_str());
+    }
+
+    JsonNode *connections = cell_node->data_dict.at("connections");
+    if (connections->type != 'D')
+        log_error("JSON connections node of \'%s\' "
+                  "in module \'%s\' is not a "
+                  "dictionary\n",
+                  cell->name.c_str(ctx), modname.c_str());
+
+    if (GetSize(pdir_node->data_dict_keys) != GetSize(connections->data_dict_keys))
+        log_error("JSON number of connections doesnt "
+                  "match number of ports in node \'%s\' "
+                  "of module \'%s\'\n",
+                  cell->name.c_str(ctx), modname.c_str());
+
+    //
+    // Loop through all of the ports of this logic element
+    //
+    for (int portid = 0; portid < GetSize(pdir_node->data_dict_keys); portid++) {
+        //
+        string port_name;
+        JsonNode *dir_node, *wire_group_node;
+        //
+
+        port_name = pdir_node->data_dict_keys[portid];
+        dir_node = pdir_node->data_dict.at(port_name);
+        wire_group_node = connections->data_dict.at(port_name);
+
+        json_import_ports(ctx, modname, netnames, cell->name.str(ctx), port_name, dir_node, wire_group_node,
+                          [cell, ctx](PortType type, const std::string &name, NetInfo *net) {
+                              cell->ports[ctx->id(name)] = PortInfo{ctx->id(name), net, type};
+                              PortRef pr;
+                              pr.cell = cell;
+                              pr.port = ctx->id(name);
+                              if (net != nullptr) {
+                                  if (type == PORT_IN || type == PORT_INOUT) {
+                                      net->users.push_back(pr);
+                                  } else if (type == PORT_OUT) {
+                                      assert(net->driver.cell == nullptr);
+                                      net->driver = pr;
+                                  }
+                              }
+                          });
+    }
+
+    ctx->cells[cell->name] = cell;
+    // check_all_nets_driven(ctx);
+}
+
+static void insert_iobuf(Context *ctx, NetInfo *net, PortType type, const string &name)
+{
+    // Instantiate a architecture-independent IO buffer connected to a given
+    // net, of a given type, and named after the IO port.
+    //
+    // During packing, this generic IO buffer will be converted to an
+    // architecure primitive.
+    //
+    CellInfo *iobuf = new CellInfo();
+    iobuf->name = ctx->id(name);
+    std::copy(net->attrs.begin(), net->attrs.end(), std::inserter(iobuf->attrs, iobuf->attrs.begin()));
+    if (type == PORT_IN) {
+        if (ctx->verbose)
+            log_info("processing input port %s\n", name.c_str());
+        iobuf->type = ctx->id("$nextpnr_ibuf");
+        iobuf->ports[ctx->id("O")] = PortInfo{ctx->id("O"), net, PORT_OUT};
+        // Special case: input, etc, directly drives inout
+        if (net->driver.cell != nullptr) {
+            assert(net->driver.cell->type == ctx->id("$nextpnr_iobuf"));
+            net = net->driver.cell->ports.at(ctx->id("I")).net;
+        }
+        assert(net->driver.cell == nullptr);
+        net->driver.port = ctx->id("O");
+        net->driver.cell = iobuf;
+    } else if (type == PORT_OUT) {
+        if (ctx->verbose)
+            log_info("processing output port %s\n", name.c_str());
+        iobuf->type = ctx->id("$nextpnr_obuf");
+        iobuf->ports[ctx->id("I")] = PortInfo{ctx->id("I"), net, PORT_IN};
+        PortRef ref;
+        ref.cell = iobuf;
+        ref.port = ctx->id("I");
+        net->users.push_back(ref);
+    } else if (type == PORT_INOUT) {
+        if (ctx->verbose)
+            log_info("processing inout port %s\n", name.c_str());
+        iobuf->type = ctx->id("$nextpnr_iobuf");
+        iobuf->ports[ctx->id("I")] = PortInfo{ctx->id("I"), nullptr, PORT_IN};
+
+        // Split the input and output nets for bidir ports
+        NetInfo *net2 = new NetInfo();
+        net2->name = ctx->id("$" + net->name.str(ctx) + "$iobuf_i");
+        net2->driver = net->driver;
+        if (net->driver.cell != nullptr) {
+            net2->driver.cell->ports[net2->driver.port].net = net2;
+            net->driver.cell = nullptr;
+        }
+        ctx->nets[net2->name] = net2;
+        iobuf->ports[ctx->id("I")].net = net2;
+        PortRef ref;
+        ref.cell = iobuf;
+        ref.port = ctx->id("I");
+        net2->users.push_back(ref);
+
+        iobuf->ports[ctx->id("O")] = PortInfo{ctx->id("O"), net, PORT_OUT};
+        assert(net->driver.cell == nullptr);
+        net->driver.port = ctx->id("O");
+        net->driver.cell = iobuf;
+    } else {
+        assert(false);
+    }
+    ctx->cells[iobuf->name] = iobuf;
+}
+
+void json_import_toplevel_port(Context *ctx, const string &modname, const std::vector<IdString> &netnames,
+                               const string &portname, JsonNode *node)
+{
+    JsonNode *dir_node = node->data_dict.at("direction");
+    JsonNode *nets_node = node->data_dict.at("bits");
+    json_import_ports(
+            ctx, modname, netnames, "Top Level IO", portname, dir_node, nets_node,
+            [ctx](PortType type, const std::string &name, NetInfo *net) { insert_iobuf(ctx, net, type, name); });
+}
+
+void json_import(Context *ctx, string modname, JsonNode *node)
+{
+    if (is_blackbox(node))
+        return;
+
+    log_info("Importing module %s\n", modname.c_str());
+
+    // Import netnames
+    std::vector<IdString> netnames;
+    if (node->data_dict.count("netnames")) {
+        JsonNode *cell_parent = node->data_dict.at("netnames");
+        for (int nnid = 0; nnid < GetSize(cell_parent->data_dict_keys); nnid++) {
+            JsonNode *here;
+
+            here = cell_parent->data_dict.at(cell_parent->data_dict_keys[nnid]);
+            std::string basename = cell_parent->data_dict_keys[nnid];
+            if (here->data_dict.count("bits")) {
+                JsonNode *bits = here->data_dict.at("bits");
+                assert(bits->type == 'A');
+                size_t num_bits = bits->data_array.size();
+                for (size_t i = 0; i < num_bits; i++) {
+                    int netid = bits->data_array.at(i)->data_number;
+                    if (netid >= int(netnames.size()))
+                        netnames.resize(netid + 1);
+                    netnames.at(netid) = ctx->id(
+                            basename + (num_bits == 1 ? "" : std::string("[") + std::to_string(i) + std::string("]")));
+                }
+            }
+        }
+    }
+
+    if (node->data_dict.count("cells")) {
+        JsonNode *cell_parent = node->data_dict.at("cells");
+        //
+        //
+        // Loop through all of the logic elements in a flattened design
+        //
+        //
+        for (int cellid = 0; cellid < GetSize(cell_parent->data_dict_keys); cellid++) {
+            JsonNode *here = cell_parent->data_dict.at(cell_parent->data_dict_keys[cellid]);
+            json_import_cell(ctx, modname, netnames, here, cell_parent->data_dict_keys[cellid]);
+        }
+    }
+
+    if (node->data_dict.count("ports")) {
+        JsonNode *ports_parent = node->data_dict.at("ports");
+
+        // N.B. ports must be imported after cells for tristate behaviour
+        // to be correct
+        // Loop through all ports
+        for (int portid = 0; portid < GetSize(ports_parent->data_dict_keys); portid++) {
+            JsonNode *here;
+
+            here = ports_parent->data_dict.at(ports_parent->data_dict_keys[portid]);
+            json_import_toplevel_port(ctx, modname, netnames, ports_parent->data_dict_keys[portid], here);
+        }
+    }
+    check_all_nets_driven(ctx);
+}
+}; // End Namespace JsonParser
+
+bool parse_json_file(std::istream &f, std::string &filename, Context *ctx)
+{
+    try {
+        using namespace JsonParser;
+
+        JsonNode root(f);
+
+        if (root.type != 'D')
+            log_error("JSON root node is not a dictionary.\n");
+
+        if (root.data_dict.count("modules") != 0) {
+            JsonNode *modules = root.data_dict.at("modules");
+
+            if (modules->type != 'D')
+                log_error("JSON modules node is not a dictionary.\n");
+
+            for (auto &it : modules->data_dict)
+                json_import(ctx, it.first, it.second);
+        }
+
+        log_info("Checksum: 0x%08x\n", ctx->checksum());
+        log_break();
+        return true;
+    } catch (log_execution_error_exception) {
+        return false;
+    }
+}
+
+NEXTPNR_NAMESPACE_END
diff --git a/json/jsonparse.h b/json/jsonparse.h
new file mode 100644
index 00000000..fe71444f
--- /dev/null
+++ b/json/jsonparse.h
@@ -0,0 +1,33 @@
+/*
+ *  nextpnr -- Next Generation Place and Route
+ *
+ *  Copyright (C) 2018  SymbioticEDA
+ *
+ *  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 JSON_PARSER
+#define JSON_PARSER
+
+#include <istream>
+#include <string>
+#include "nextpnr.h"
+
+NEXTPNR_NAMESPACE_BEGIN
+
+extern bool parse_json_file(std::istream &, std::string &, Context *);
+
+NEXTPNR_NAMESPACE_END
+
+#endif