mistral: First pass at carry packing

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

mistral/archdefs.h

@@ -183,6 +183,7 @@ struct ArchCellInfo : BaseClusterInfo
             int lut_bits_count;
 
             bool is_carry, is_shared, is_extended;
+            bool carry_start, carry_end;
         } combInfo;
         struct
         {

mistral/constids.inc

@@ -39,9 +39,9 @@ X(Q)
 
 X(COMBOUT)
 X(SUM_OUT)
-X(CIN)
+X(CI)
 X(SHAREIN)
-X(COUT)
+X(CO)
 X(SHAREOUT)
 
 X(CARRY_START)
@@ -64,8 +64,6 @@ X(LUT1)
 
 X(D0)
 X(D1)
-X(CI)
-X(CO)
 X(SO)
 
 X(WIRE)

mistral/lab.cc

@@ -48,7 +48,7 @@ static void create_alm(Arch *arch, int x, int y, int z, uint32_t lab_idx)
                 share_in = arch->add_wire(x, y, id_CARRY_START);
             } else {
                 // Output of last tile
-                carry_in = arch->add_wire(x, y - 1, id_COUT);
+                carry_in = arch->add_wire(x, y - 1, id_CO);
                 share_in = arch->add_wire(x, y - 1, id_SHAREOUT);
             }
         } else {
@@ -57,7 +57,7 @@ static void create_alm(Arch *arch, int x, int y, int z, uint32_t lab_idx)
             share_in = arch->add_wire(x, y, arch->id(stringf("SHARE[%d]", (z * 2 + i) - 1)));
         }
         if (z == 9 && i == 1) {
-            carry_out = arch->add_wire(x, y, id_COUT);
+            carry_out = arch->add_wire(x, y, id_CO);
             share_out = arch->add_wire(x, y, id_SHAREOUT);
         } else {
             carry_out = arch->add_wire(x, y, arch->id(stringf("CARRY[%d]", z * 2 + i)));
@@ -75,9 +75,9 @@ static void create_alm(Arch *arch, int x, int y, int z, uint32_t lab_idx)
         arch->add_bel_pin(bel, id_F0, PORT_IN, arch->get_port(CycloneV::LAB, x, y, z, CycloneV::F0));
         arch->add_bel_pin(bel, id_F1, PORT_IN, arch->get_port(CycloneV::LAB, x, y, z, CycloneV::F1));
         // Carry/share chain
-        arch->add_bel_pin(bel, id_CIN, PORT_IN, carry_in);
+        arch->add_bel_pin(bel, id_CI, PORT_IN, carry_in);
         arch->add_bel_pin(bel, id_SHAREIN, PORT_IN, share_in);
-        arch->add_bel_pin(bel, id_COUT, PORT_OUT, carry_out);
+        arch->add_bel_pin(bel, id_CO, PORT_OUT, carry_out);
         arch->add_bel_pin(bel, id_SHAREOUT, PORT_OUT, share_out);
         // Combinational output
         alm.comb_out[i] = arch->add_wire(x, y, arch->id(stringf("COMBOUT[%d]", z * 2 + i)));
@@ -231,6 +231,8 @@ void Arch::assign_comb_info(CellInfo *cell) const
     cell->combInfo.is_carry = false;
     cell->combInfo.is_shared = false;
     cell->combInfo.is_extended = false;
+    cell->combInfo.carry_start = false;
+    cell->combInfo.carry_end = false;
 
     if (cell->type == id_MISTRAL_ALUT_ARITH) {
         cell->combInfo.is_carry = true;
@@ -241,7 +243,13 @@ void Arch::assign_comb_info(CellInfo *cell) const
         for (auto pin : {id_A, id_B, id_C, id_D0, id_D1}) {
             cell->combInfo.lut_in[i++] = get_net_or_empty(cell, pin);
         }
+
+        const NetInfo *ci = get_net_or_empty(cell, id_CI);
+        const NetInfo *co = get_net_or_empty(cell, id_CO);
+
         cell->combInfo.comb_out = get_net_or_empty(cell, id_SO);
+        cell->combInfo.carry_start = (ci == nullptr) || (ci->driver.cell == nullptr);
+        cell->combInfo.carry_end = (co == nullptr) || (co->users.empty());
     } else {
         cell->combInfo.lut_input_count = 0;
         switch (cell->type.index) {
@@ -296,6 +304,22 @@ void Arch::assign_ff_info(CellInfo *cell) const
     cell->ffInfo.datain = get_net_or_empty(cell, id_DATAIN);
 }
 
+namespace {
+// Check if the other side of a carry chain wire is being used
+bool carry_used(const Arch *arch, BelId bel, IdString pin)
+{
+    WireId wire = arch->getBelPinWire(bel, pin);
+    for (auto bp : arch->getWireBelPins(wire)) {
+        if (bp.bel == bel)
+            continue;
+        CellInfo *ci = arch->getBoundBelCell(bp.bel);
+        if (ci != nullptr && ci->combInfo.is_carry)
+            return true;
+    }
+    return false;
+}
+} // namespace
+
 // Validity checking functions
 bool Arch::is_alm_legal(uint32_t lab, uint8_t alm) const
 {
@@ -342,6 +366,16 @@ bool Arch::is_alm_legal(uint32_t lab, uint8_t alm) const
             return false;
     }
 
+    // Never allow two disjoint carry chains to accidentally stack
+    for (int i = 0; i < 2; i++) {
+        if (!luts[i])
+            continue;
+        if (luts[i]->combInfo.carry_start && carry_used(this, alm_data.lut_bels[i], id_CI))
+            return false;
+        if (luts[i]->combInfo.carry_end && carry_used(this, alm_data.lut_bels[i], id_CO))
+            return false;
+    }
+
     // For each ALM half; check FF control set sharing and input routeability
     for (int i = 0; i < 2; i++) {
         // There are two ways to route from the fabric into FF data - either routing through a LUT or using the E/F

mistral/pack.cc

@@ -275,11 +275,52 @@ struct MistralPacker
         }
     }
 
+    void constrain_carries()
+    {
+        for (auto cell : sorted(ctx->cells)) {
+            CellInfo *ci = cell.second;
+            if (ci->type != id_MISTRAL_ALUT_ARITH)
+                continue;
+            const NetInfo *cin = get_net_or_empty(ci, id_CI);
+            if (cin != nullptr && cin->driver.cell != nullptr)
+                continue; // not the start of a chain
+            std::vector<CellInfo *> chain;
+            CellInfo *cursor = ci;
+            while (true) {
+                chain.push_back(cursor);
+                const NetInfo *co = get_net_or_empty(cursor, id_CO);
+                if (co == nullptr || co->users.empty())
+                    break;
+                if (co->users.size() > 1)
+                    log_error("Carry net %s has more than one sink!\n", ctx->nameOf(co));
+                auto &usr = co->users.at(0);
+                if (usr.port != id_CI)
+                    log_error("Carry net %s drives port %s, expected CI\n", ctx->nameOf(co), ctx->nameOf(usr.port));
+                cursor = usr.cell;
+            }
+
+            chain.at(0)->constr_abs_z = true;
+            chain.at(0)->constr_z = 0;
+            chain.at(0)->cluster = chain.at(0)->name;
+
+            for (int i = 1; i < int(chain.size()); i++) {
+                chain.at(i)->constr_x = 0;
+                chain.at(i)->constr_y = (i / 20);
+                // 2 COMB, 4 FF per ALM
+                chain.at(i)->constr_z = ((i / 2) % 10) * 6 + (i % 2);
+                chain.at(i)->constr_abs_z = true;
+                chain.at(i)->cluster = chain.at(0)->name;
+                chain.at(0)->constr_children.push_back(chain.at(i));
+            }
+        }
+    }
+
     void run()
     {
         init_constant_nets();
         pack_constants();
         pack_io();
+        constrain_carries();
     }
 };
 }; // namespace