nexus: LUT permutation support

Signed-off-by: gatecat <gatecat@ds0.me>

4 files changed, 72 insertions, 4 deletions

diff --git a/nexus/arch.cc b/nexus/arch.cc
index fa81485a..95474800 100644
--- a/nexus/arch.cc
+++ b/nexus/arch.cc
@@ -1030,7 +1030,7 @@ const std::vector<std::string> Arch::availablePlacers = {"sa",
 
 };
 
-const std::string Arch::defaultRouter = "router2";
+const std::string Arch::defaultRouter = "router1";
 const std::vector<std::string> Arch::availableRouters = {"router1", "router2"};
 
 NEXTPNR_NAMESPACE_END
diff --git a/nexus/arch.h b/nexus/arch.h
index deb9b6db..300c3760 100644
--- a/nexus/arch.h
+++ b/nexus/arch.h
@@ -86,6 +86,7 @@ NPNR_PACKED_STRUCT(struct LocWireInfoPOD {
 enum PipFlags
 {
     PIP_FIXED_CONN = 0x8000,
+    PIP_LUT_PERM = 0x4000,
 };
 
 NPNR_PACKED_STRUCT(struct PipInfoPOD {
@@ -979,10 +980,38 @@ struct Arch : BaseArch<ArchRanges>
         return tileStatus[bel.tile].boundcells[bel.index] == nullptr;
     }
 
+    bool is_pseudo_pip_disabled(PipId pip) const
+    {
+        const auto &data = pip_data(pip);
+        if (data.flags & PIP_LUT_PERM) {
+            int lut_idx = (data.flags >> 8) & 0xF;
+            int from_pin = (data.flags >> 4) & 0xF;
+            int to_pin = (data.flags >> 0) & 0xF;
+            auto &ts = tileStatus.at(pip.tile);
+            if (!ts.lts)
+                return false;
+            const CellInfo *lut = ts.lts->cells[((lut_idx / 2) << 3) | (BEL_LUT0 + (lut_idx % 2))];
+            if (lut) {
+                if (lut->lutInfo.is_memory)
+                    return true;
+                if (lut->lutInfo.is_carry && (from_pin == 3 || to_pin == 3))
+                    return true; // Upper pin is special for carries
+            }
+            if (lut_idx == 4 || lut_idx == 5) {
+                const CellInfo *ramw = ts.lts->cells[((lut_idx / 2) << 3) | BEL_RAMW];
+                if (ramw)
+                    return true; // Don't permute RAM write address
+            }
+        }
+        return false;
+    }
+
     bool checkPipAvail(PipId pip) const override
     {
         if (disabled_pips.count(pip))
             return false;
+        if (is_pseudo_pip_disabled(pip))
+            return false;
         return BaseArch::checkPipAvail(pip);
     }
 
@@ -990,6 +1019,8 @@ struct Arch : BaseArch<ArchRanges>
     {
         if (disabled_pips.count(pip))
             return false;
+        if (is_pseudo_pip_disabled(pip))
+            return false;
         return BaseArch::checkPipAvailForNet(pip, net);
     }
 
diff --git a/nexus/bba_version.inc b/nexus/bba_version.inc
index f599e28b..b4de3947 100644
--- a/nexus/bba_version.inc
+++ b/nexus/bba_version.inc
@@ -1 +1 @@
-10
+11
diff --git a/nexus/fasm.cc b/nexus/fasm.cc
index 964828cb..bb0a7941 100644
--- a/nexus/fasm.cc
+++ b/nexus/fasm.cc
@@ -207,7 +207,7 @@ struct NexusFasmWriter
     void write_pip(PipId pip)
     {
         auto &pd = ctx->pip_data(pip);
-        if (pd.flags & PIP_FIXED_CONN)
+        if ((pd.flags & PIP_FIXED_CONN) || (pd.flags & PIP_LUT_PERM))
             return;
         std::string tile = tile_name(pip.tile, tile_by_type_and_loc(pip.tile, IdString(pd.tile_type)));
         std::string source_wire = escape_name(ctx->pip_src_wire_name(pip).str(ctx));
@@ -317,6 +317,43 @@ struct NexusFasmWriter
         }
     }
 
+    unsigned permute_init(const CellInfo *cell)
+    {
+        unsigned orig_init = int_or_default(cell->params, id_INIT, 0);
+        std::array<std::vector<unsigned>, 4> phys_to_log;
+        const std::array<IdString, 4> ports{id_A, id_B, id_C, id_D};
+        for (unsigned i = 0; i < 4; i++) {
+            WireId pin_wire = ctx->getBelPinWire(cell->bel, ports[i]);
+            for (PipId pip : ctx->getPipsUphill(pin_wire)) {
+                if (!ctx->getBoundPipNet(pip))
+                    continue;
+                const auto &data = ctx->pip_data(pip);
+                if (data.flags & PIP_FIXED_CONN) { // non-permuting
+                    phys_to_log[i].push_back(i);
+                } else { // permuting
+                    NPNR_ASSERT(data.flags & PIP_LUT_PERM);
+                    unsigned from_pin = (data.flags >> 4) & 0xF;
+                    unsigned to_pin = (data.flags >> 0) & 0xF;
+                    NPNR_ASSERT(to_pin == i);
+                    phys_to_log[from_pin].push_back(i);
+                }
+            }
+        }
+        unsigned permuted_init = 0;
+        for (unsigned i = 0; i < 16; i++) {
+            unsigned log_idx = 0;
+            for (unsigned j = 0; j < 4; j++) {
+                if ((i >> j) & 0x1) {
+                    for (auto log_pin : phys_to_log[j])
+                        log_idx |= (1 << log_pin);
+                }
+            }
+            if ((orig_init >> log_idx) & 0x1)
+                permuted_init |= (1 << i);
+        }
+        return permuted_init;
+    }
+
     // Write config for an OXIDE_COMB cell
     void write_comb(const CellInfo *cell)
     {
@@ -327,7 +364,7 @@ struct NexusFasmWriter
         push_tile(bel.tile, id_PLC);
         push(stringf("SLICE%c", slice));
         if (cell->params.count(id_INIT))
-            write_int_vector(stringf("K%d.INIT[15:0]", k), int_or_default(cell->params, id_INIT, 0), 16);
+            write_int_vector(stringf("K%d.INIT[15:0]", k), permute_init(cell), 16);
         if (cell->lutInfo.is_carry) {
             write_bit("MODE.CCU2");
             write_enum(cell, "CCU2.INJECT", "NO");