diff --git a/nexus/arch.cc b/nexus/arch.cc
index dfcf9510..f309c872 100644
--- a/nexus/arch.cc
+++ b/nexus/arch.cc
@@ -117,6 +117,22 @@ Arch::Arch(ArchArgs args) : args(args)
     for (size_t i = 0; i < chip_info->num_tiles; i++) {
         tileStatus[i].boundcells.resize(db->loctypes[chip_info->grid[i].loc_type].num_bels);
     }
+    // Validate and set up package
+    package_idx = -1;
+    for (size_t i = 0; i < chip_info->num_packages; i++) {
+        if (package == chip_info->packages[i].short_name.get()) {
+            package_idx = i;
+            break;
+        }
+    }
+    if (package_idx == -1) {
+        std::string all_packages = "";
+        for (size_t i = 0; i < chip_info->num_packages; i++) {
+            all_packages += " ";
+            all_packages += chip_info->packages[i].short_name.get();
+        }
+        log_error("Unknown package '%s'. Available package options:%s\n", package.c_str(), all_packages.c_str());
+    }
 }
 
 // -----------------------------------------------------------------------
@@ -487,6 +503,79 @@ void Arch::set_cell_pinmux(CellInfo *cell, IdString pin, CellPinMux state)
 
 // -----------------------------------------------------------------------
 
+const PadInfoPOD *Arch::get_pin_data(const std::string &pin) const
+{
+    for (size_t i = 0; i < chip_info->num_pads; i++) {
+        const PadInfoPOD *pad = &(chip_info->pads[i]);
+        if (pin == pad->pins[package_idx].get())
+            return pad;
+    }
+    return nullptr;
+}
+
+Loc Arch::get_pad_loc(const PadInfoPOD *pad) const
+{
+    Loc loc;
+    switch (pad->side) {
+    case PIO_LEFT:
+        loc.x = 0;
+        loc.y = pad->offset;
+        break;
+    case PIO_RIGHT:
+        loc.x = chip_info->width - 1;
+        loc.y = pad->offset;
+        break;
+    case PIO_TOP:
+        loc.x = pad->offset;
+        loc.y = 0;
+        break;
+    case PIO_BOTTOM:
+        loc.x = pad->offset;
+        loc.y = chip_info->height - 1;
+    }
+    loc.z = pad->pio_index;
+    return loc;
+}
+
+BelId Arch::get_pin_bel(const std::string &pin) const
+{
+    const PadInfoPOD *pad = get_pin_data(pin);
+    if (pad == nullptr)
+        return BelId();
+    return getBelByLocation(get_pad_loc(pad));
+}
+
+const PadInfoPOD *Arch::get_bel_pad(BelId bel) const
+{
+    Loc loc = getBelLocation(bel);
+    int side = -1, offset = -1;
+    // Convert (x, y) to (side, offset)
+    if (loc.x == 0) {
+        side = PIO_LEFT;
+        offset = loc.y;
+    } else if (loc.x == (chip_info->width - 1)) {
+        side = PIO_RIGHT;
+        offset = loc.y;
+    } else if (loc.y == 0) {
+        side = PIO_TOP;
+        offset = loc.x;
+    } else if (loc.y == (chip_info->height - 1)) {
+        side = PIO_BOTTOM;
+        offset = loc.x;
+    } else {
+        return nullptr;
+    }
+    // Lookup in the list of pads
+    for (size_t i = 0; i < chip_info->num_pads; i++) {
+        const PadInfoPOD *pad = &(chip_info->pads[i]);
+        if (pad->side == side && pad->offset == offset && pad->pio_index == loc.z)
+            return pad;
+    }
+    return nullptr;
+}
+
+// -----------------------------------------------------------------------
+
 #ifdef WITH_HEAP
 const std::string Arch::defaultPlacer = "heap";
 #else
diff --git a/nexus/arch.h b/nexus/arch.h
index 89723853..886ee557 100644
--- a/nexus/arch.h
+++ b/nexus/arch.h
@@ -258,6 +258,8 @@ NPNR_PACKED_STRUCT(struct ChipInfoPOD {
     uint16_t width;
     uint16_t height;
     uint32_t num_tiles;
+    uint32_t num_pads;
+    uint32_t num_packages;
     RelPtr<GridLocationPOD> grid;
     RelPtr<GlobalInfoPOD> globals;
     RelPtr<PadInfoPOD> pads;
@@ -827,6 +829,8 @@ struct Arch : BaseCtx
     const DatabasePOD *db;
     const ChipInfoPOD *chip_info;
 
+    int package_idx;
+
     // Binding states
     struct LogicTileStatus
     {
@@ -1430,6 +1434,13 @@ struct Arch : BaseCtx
 
     // -------------------------------------------------
 
+    const PadInfoPOD *get_pin_data(const std::string &pin) const;
+    Loc get_pad_loc(const PadInfoPOD *pad) const;
+    BelId get_pin_bel(const std::string &pin) const;
+    const PadInfoPOD *get_bel_pad(BelId bel) const;
+
+    // -------------------------------------------------
+
     // List of IO constraints, used by PDC parser
     std::unordered_map<IdString, std::unordered_map<IdString, Property>> io_attr;
 
diff --git a/nexus/bba_version.inc b/nexus/bba_version.inc
index 7ed6ff82..1e8b3149 100644
--- a/nexus/bba_version.inc
+++ b/nexus/bba_version.inc
@@ -1 +1 @@
-5
+6
diff --git a/nexus/pack.cc b/nexus/pack.cc
index 602457f5..688d74ab 100644
--- a/nexus/pack.cc
+++ b/nexus/pack.cc
@@ -473,6 +473,23 @@ struct NexusPacker
         }
     }
 
+    void pack_io()
+    {
+        for (auto cell : sorted(ctx->cells)) {
+            CellInfo *ci = cell.second;
+            if (ci->type == id_SEIO33_CORE || ci->type == id_SEIO18_CORE) {
+                auto fnd_loc = ci->attrs.find(id_LOC);
+                if (fnd_loc == ci->attrs.end())
+                    continue;
+                BelId bel = ctx->get_pin_bel(fnd_loc->second.as_string());
+                if (bel == BelId())
+                    log_error("cannot constrain IO '%s', no PIO pin named '%s'\n", ctx->nameOf(ci),
+                              fnd_loc->second.as_string().c_str());
+                ci->attrs[id_BEL] = ctx->getBelName(bel).str(ctx);
+            }
+        }
+    }
+
     explicit NexusPacker(Context *ctx) : ctx(ctx) {}
 
     void operator()()
@@ -480,6 +497,7 @@ struct NexusPacker
         ctx->get_cell_pin_data(cell_db);
         pack_ffs();
         pack_luts();
+        pack_io();
     }
 };