Remove IO buffers when fed by SB_IO

Signed-off-by: David Shah <davey1576@gmail.com>

common/design_utils.h

@@ -22,6 +22,8 @@
 #ifndef DESIGN_UTILS_H
 #define DESIGN_UTILS_H
 
+#include <algorithm>
+
 NEXTPNR_NAMESPACE_BEGIN
 
 /*
@@ -35,23 +37,36 @@ void replace_port(CellInfo *old_cell, IdString old_name, CellInfo *rep_cell,
 // If a net drives a given port of a cell matching a predicate (in many
 // cases more than one cell type, e.g. SB_DFFxx so a predicate is used), return
 // the first instance of that cell (otherwise nullptr). If exclusive is set to
-// true, then this cell must be the only load
+// true, then this cell must be the only load. If ignore_cell is set, that cell
+// is not considered
 template <typename F1>
 CellInfo *net_only_drives(NetInfo *net, F1 cell_pred, IdString port,
-                          bool exclusive = false)
+                          bool exclusive = false, CellInfo *exclude = nullptr)
 {
     if (net == nullptr)
         return nullptr;
-    if (exclusive && (net->users.size() != 1)) {
+    if (exclusive) {
-        return nullptr;
+        if (exclude == nullptr) {
-    } else {
+            if (net->users.size() != 1)
-        for (const auto &load : net->users) {
+                return nullptr;
-            if (cell_pred(load.cell) && load.port == port) {
+        } else {
-                return load.cell;
+            if (net->users.size() > 2) {
+                return nullptr;
+            } else if (net->users.size() == 2) {
+                if (std::find_if(net->users.begin(), net->users.end(),
+                                 [exclude](const PortRef &ref) {
+                                     return ref.cell == exclude;
+                                 }) == net->users.end())
+                    return nullptr;
             }
         }
-        return nullptr;
     }
+    for (const auto &load : net->users) {
+        if (load.cell != exclude && cell_pred(load.cell) && load.port == port) {
+            return load.cell;
+        }
+    }
+    return nullptr;
 }
 
 // If a net is driven by a given port of a cell matching a predicate, return

frontend/json/jsonparse.cc

@@ -693,12 +693,16 @@ static void insert_iobuf(Design *design, NetInfo *net, PortType type,
     design->cells[iobuf->name] = iobuf;
 }
 
-void json_import_toplevel_port(Design *design, const string &modname, const string& portname, JsonNode *node) {
+void json_import_toplevel_port(Design *design, const string &modname,
+                               const string &portname, JsonNode *node)
+{
     JsonNode *dir_node = node->data_dict.at("direction");
     JsonNode *nets_node = node->data_dict.at("bits");
-    json_import_ports(design, modname, "Top Level IO", portname, dir_node, nets_node, [design](PortType type, const std::string &name, NetInfo *net){
+    json_import_ports(
-        insert_iobuf(design, net, type, name);
+            design, modname, "Top Level IO", portname, dir_node, nets_node,
-    });
+            [design](PortType type, const std::string &name, NetInfo *net) {
+                insert_iobuf(design, net, type, name);
+            });
 }
 
 void json_import(Design *design, string modname, JsonNode *node)
@@ -738,7 +742,9 @@ void json_import(Design *design, string modname, JsonNode *node)
 
             here = ports_parent->data_dict.at(
                     ports_parent->data_dict_keys[portid]);
-            json_import_toplevel_port(design, modname, ports_parent->data_dict_keys[portid], here);
+            json_import_toplevel_port(design, modname,
+                                      ports_parent->data_dict_keys[portid],
+                                      here);
         }
     }
     check_all_nets_driven(design);

ice40/cells.h

@@ -47,6 +47,9 @@ inline bool is_ff(const CellInfo *cell)
            cell->type == "SB_DFFNESS" || cell->type == "SB_DFFNES";
 }
 
+// Return true if a cell is a SB_IO
+inline bool is_sb_io(const CellInfo *cell) { return cell->type == "SB_IO"; }
+
 // Convert a SB_LUT primitive to (part of) an ICESTORM_LC, swapping ports
 // as needed. Set no_dff if a DFF is not being used, so that the output
 // can be reconnected

ice40/pack.cc

@@ -134,10 +134,69 @@ static void pack_constants(Design *design)
     }
 }
 
+static bool is_nextpnr_iob(CellInfo *cell)
+{
+    return cell->type == "$nextpnr_ibuf" || cell->type == "$nextpnr_obuf" ||
+           cell->type == "$nextpnr_iobuf";
+}
+
+// Pack IO buffers
+static void pack_io(Design *design)
+{
+    std::unordered_set<IdString> packed_cells;
+    std::vector<CellInfo *> new_cells;
+
+    for (auto cell : design->cells) {
+        CellInfo *ci = cell.second;
+        if (is_nextpnr_iob(ci)) {
+            if (ci->type == "$nextpnr_ibuf" || ci->type == "$nextpnr_iobuf") {
+                CellInfo *sb = net_only_drives(ci->ports.at("O").net, is_sb_io,
+                                               "PACKAGE_PIN", true, ci);
+                if (sb != nullptr) {
+                    // Trivial case, SB_IO used. Just destroy the net and the
+                    // iobuf
+                    packed_cells.insert(ci->name);
+                    log_info("%s feeds SB_IO %s, removing %s %s.\n",
+                             ci->name.c_str(), sb->name.c_str(),
+                             ci->type.c_str(), ci->name.c_str());
+                    NetInfo *net = sb->ports.at("PACKAGE_PIN").net;
+                    if (net != nullptr) {
+                        design->nets.erase(net->name);
+                        sb->ports.at("PACKAGE_PIN").net = nullptr;
+                    }
+                }
+            } else if (ci->type == "$nextpnr_obuf") {
+                CellInfo *sb = net_only_drives(ci->ports.at("I").net, is_sb_io,
+                                               "PACKAGE_PIN", true, ci);
+                if (sb != nullptr) {
+                    // Trivial case, SB_IO used. Just destroy the net and the
+                    // iobuf
+                    packed_cells.insert(ci->name);
+                    log_info("%s feeds SB_IO %s, removing %s %s.\n",
+                             ci->name.c_str(), sb->name.c_str(),
+                             ci->type.c_str(), ci->name.c_str());
+                    NetInfo *net = sb->ports.at("PACKAGE_PIN").net;
+                    if (net != nullptr) {
+                        design->nets.erase(net->name);
+                        sb->ports.at("PACKAGE_PIN").net = nullptr;
+                    }
+                }
+            }
+        }
+    }
+    for (auto pcell : packed_cells) {
+        design->cells.erase(pcell);
+    }
+    for (auto ncell : new_cells) {
+        design->cells[ncell->name] = ncell;
+    }
+}
+
 // Main pack function
 void pack_design(Design *design)
 {
     pack_constants(design);
+    pack_io(design);
     pack_lut_lutffs(design);
     pack_nonlut_ffs(design);
 }

ice40/pack_tests/io_wrapper.v

@@ -153,7 +153,7 @@ module io_wrapper(input clk_pin, cen_pin, rst_pin, ina_pin, inb_pin,
         .PULLUP(1'b0),
         .NEG_TRIGGER(1'b0)
     ) outd_iob (
-        .PACKAGE_PIN(outa_pin),
+        .PACKAGE_PIN(outd_pin),
         .LATCH_INPUT_VALUE(),
         .CLOCK_ENABLE(),
         .INPUT_CLK(),