diff --git a/common/kernel/relptr.h b/common/kernel/relptr.h
index f0f45b7d03..4a98dd682b 100644
--- a/common/kernel/relptr.h
+++ b/common/kernel/relptr.h
@@ -33,6 +33,8 @@ template <typename T> struct RelPtr
 
     const T *get() const { return reinterpret_cast<const T *>(reinterpret_cast<const char *>(this) + offset); }
 
+    bool is_null() const { return offset == 0; }
+
     const T &operator[](std::size_t index) const { return get()[index]; }
 
     const T &operator*() const { return *(get()); }
diff --git a/himbaechel/chipdb.h b/himbaechel/chipdb.h
index 2ac7f60b42..17430ac4c2 100644
--- a/himbaechel/chipdb.h
+++ b/himbaechel/chipdb.h
@@ -138,6 +138,7 @@ NPNR_PACKED_STRUCT(struct PadInfoPOD {
 NPNR_PACKED_STRUCT(struct PackageInfoPOD {
     int32_t name;
     RelSlice<PadInfoPOD> pads;
+    RelPtr<uint8_t> extra_data;
 });
 
 NPNR_PACKED_STRUCT(struct TileInstPOD {
diff --git a/himbaechel/himbaechel_dbgen/chip.py b/himbaechel/himbaechel_dbgen/chip.py
index 19aa8914d6..8650813d93 100644
--- a/himbaechel/himbaechel_dbgen/chip.py
+++ b/himbaechel/himbaechel_dbgen/chip.py
@@ -411,6 +411,7 @@ class PackageInfo(BBAStruct):
     strs: StringPool
     name: IdString
     pads: list[int] = field(default_factory=list)
+    extra_data: object = None
 
     def create_pad(self, package_pin: str, tile: str, bel: str, pad_function: str, pad_bank: int, flags: int = 0):
         pad = PadInfo(package_pin = self.strs.id(package_pin), tile = self.strs.id(tile), bel = self.strs.id(bel),
@@ -424,10 +425,18 @@ def serialise_lists(self, context: str, bba: BBAWriter):
         bba.label(f"{context}_pads")
         for i, pad in enumerate(self.pads):
             pad.serialise(f"{context}_pad{i}", bba)
+        if self.extra_data is not None:
+            self.extra_data.serialise_lists(f"{context}_extra_data", bba)
+            bba.label(f"{context}_extra_data")
+            self.extra_data.serialise(f"{context}_extra_data", bba)
 
     def serialise(self, context: str, bba: BBAWriter):
         bba.u32(self.name.index)
         bba.slice(f"{context}_pads", len(self.pads))
+        if self.extra_data is not None:
+            bba.ref(f"{context}_extra_data")
+        else:
+            bba.u32(0)
 
 class TimingValue(BBAStruct):
     def __init__(self, fast_min=0, fast_max=None, slow_min=None, slow_max=None):
diff --git a/himbaechel/uarch/gowin/cst.cc b/himbaechel/uarch/gowin/cst.cc
index a933cc19c6..5229a4c2a5 100644
--- a/himbaechel/uarch/gowin/cst.cc
+++ b/himbaechel/uarch/gowin/cst.cc
@@ -240,8 +240,38 @@ struct GowinCstReader
     }
 };
 
+
+static void add_sip_constraints(Context *ctx, const Extra_package_data_POD *extra) {
+    for(auto cst : extra->cst) {
+        auto it = ctx->cells.find(IdString(cst.net));
+        if (it == ctx->cells.end()) {
+            log_info("Cell %s not found\n", IdString(cst.net).c_str(ctx));
+            continue;
+        }
+        Loc loc = Loc(cst.col, cst.row, cst.bel);
+        BelId bel = ctx->getBelByLocation(loc);
+        if (bel == BelId()) {
+            log_error("Pin not found.\n");
+        }
+        it->second->setAttr(IdString(ID_BEL), std::string(ctx->nameOfBel(bel)));
+
+        if(cst.iostd > 0) {
+            std::string attr = "&IO_TYPE=";
+            attr += IdString(cst.iostd).c_str(ctx);
+            boost::algorithm::to_upper(attr);
+            it->second->setAttr(ctx->id(attr), 1);
+        }
+    }
+}
+
 bool gowin_apply_constraints(Context *ctx, std::istream &in)
 {
+    // implicit constraints from SiP pins
+    if(!ctx->package_info->extra_data.is_null()) {
+        const Extra_package_data_POD *extra = reinterpret_cast<const Extra_package_data_POD *>(ctx->package_info->extra_data.get());
+        add_sip_constraints(ctx, extra);
+    }
+
     GowinCstReader reader(ctx, in);
     return reader.run();
 }
diff --git a/himbaechel/uarch/gowin/gowin.h b/himbaechel/uarch/gowin/gowin.h
index 1588b27b91..001c1cfb07 100644
--- a/himbaechel/uarch/gowin/gowin.h
+++ b/himbaechel/uarch/gowin/gowin.h
@@ -130,6 +130,18 @@ NPNR_PACKED_STRUCT(struct Wire_bel_POD {
     int32_t side;
 });
 
+NPNR_PACKED_STRUCT(struct Constraint_POD {
+    int32_t net;
+    int32_t row;
+    int32_t col;
+    int32_t bel;
+    int32_t iostd;
+});
+
+NPNR_PACKED_STRUCT(struct Extra_package_data_POD {
+    RelSlice<Constraint_POD> cst;
+});
+
 NPNR_PACKED_STRUCT(struct Extra_chip_data_POD {
     int32_t chip_flags;
     Bottom_io_POD bottom_io;
diff --git a/himbaechel/uarch/gowin/gowin_arch_gen.py b/himbaechel/uarch/gowin/gowin_arch_gen.py
index 7daed96354..473efa21a9 100644
--- a/himbaechel/uarch/gowin/gowin_arch_gen.py
+++ b/himbaechel/uarch/gowin/gowin_arch_gen.py
@@ -244,6 +244,23 @@ def serialise(self, context: str, bba: BBAWriter):
         bba.slice(f"{context}_dcs_bels", len(self.dcs_bels))
         bba.slice(f"{context}_dhcen_bels", len(self.dhcen_bels))
 
+@dataclass
+class PackageExtraData(BBAStruct):
+    strs: StringPool
+    cst: list
+
+    def serialise_lists(self, context: str, bba: BBAWriter):
+        bba.label(f"{context}_constraints")
+        for (net, row, col, bel, iostd) in self.cst:
+            bba.u32(self.strs.id(net).index)
+            bba.u32(row)
+            bba.u32(col)
+            bba.u32(ord(bel[0])-ord('A')+IOBA_Z)
+            bba.u32(self.strs.id(iostd).index if iostd else 0)
+
+    def serialise(self, context: str, bba: BBAWriter):
+        bba.slice(f"{context}_constraints", len(self.cst))
+
 @dataclass
 class PadExtraData(BBAStruct):
     # Which PLL does this pad belong to.
@@ -1206,6 +1223,10 @@ def ioloc_to_tile_bel(ioloc):
             continue
         created_pkgs.add(partno)
         pkg = chip.create_package(partno)
+
+        if variant in db.sip_cst and pkgname in db.sip_cst[variant]:
+            pkg.extra_data = PackageExtraData(chip.strs, db.sip_cst[variant][pkgname])
+
         for pinno, pininfo in db.pinout[variant][pkgname].items():
             io_loc, cfgs = pininfo
             tile, bel = ioloc_to_tile_bel(io_loc)