mistral: Add some packing logic based on nexus

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

4 files changed, 202 insertions, 3 deletions

diff --git a/mistral/archdefs.cc b/mistral/archdefs.cc
new file mode 100644
index 00000000..8a2bbe7a
--- /dev/null
+++ b/mistral/archdefs.cc
@@ -0,0 +1,33 @@
+/*
+ *  nextpnr -- Next Generation Place and Route
+ *
+ *  Copyright (C) 2021 gatecat <gatecat@ds0.me>
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#include "nextpnr.h"
+
+NEXTPNR_NAMESPACE_BEGIN
+
+CellPinState ArchCellInfo::get_pin_state(IdString pin) const
+{
+    auto fnd = pin_data.find(pin);
+    if (fnd != pin_data.end())
+        return fnd->second.state;
+    else
+        return PIN_SIG;
+}
+
+NEXTPNR_NAMESPACE_END
diff --git a/mistral/archdefs.h b/mistral/archdefs.h
index 2ae1bccb..ab00cb26 100644
--- a/mistral/archdefs.h
+++ b/mistral/archdefs.h
@@ -192,6 +192,8 @@ struct ArchCellInfo : BaseClusterInfo
     };
 
     std::unordered_map<IdString, ArchPinInfo> pin_data;
+
+    CellPinState get_pin_state(IdString pin) const;
 };
 
 NEXTPNR_NAMESPACE_END
diff --git a/mistral/constids.inc b/mistral/constids.inc
index c4af45e6..c17d9f89 100644
--- a/mistral/constids.inc
+++ b/mistral/constids.inc
@@ -58,6 +58,9 @@ X(MISTRAL_NOT)
 X(MISTRAL_BUF)
 X(MISTRAL_CONST)
 X(MISTRAL_ALUT_ARITH)
+X(LUT)
+X(LUT0)
+X(LUT1)
 
 X(D0)
 X(D1)
@@ -65,4 +68,7 @@ X(CI)
 X(CO)
 X(SO)
 
-X(WIRE)
\ No newline at end of file
+X(WIRE)
+
+X(GND)
+X(VCC)
diff --git a/mistral/pack.cc b/mistral/pack.cc
index 78a000d9..be0128fe 100644
--- a/mistral/pack.cc
+++ b/mistral/pack.cc
@@ -17,18 +17,176 @@
  *
  */
 
+#include "design_utils.h"
 #include "log.h"
 #include "nextpnr.h"
 #include "util.h"
 
 NEXTPNR_NAMESPACE_BEGIN
+namespace {
+struct MistralPacker
+{
+    MistralPacker(Context *ctx) : ctx(ctx){};
+    Context *ctx;
+
+    NetInfo *gnd_net, *vcc_net;
+
+    void init_constant_nets()
+    {
+        CellInfo *gnd_drv = ctx->createCell(ctx->id("$PACKER_GND_DRV"), id_MISTRAL_CONST);
+        gnd_drv->params[id_LUT] = 0;
+        gnd_drv->addOutput(id_Q);
+        CellInfo *vcc_drv = ctx->createCell(ctx->id("$PACKER_VCC_DRV"), id_MISTRAL_CONST);
+        vcc_drv->params[id_LUT] = 1;
+        vcc_drv->addOutput(id_Q);
+        gnd_net = ctx->createNet(ctx->id("$PACKER_GND_NET"));
+        vcc_net = ctx->createNet(ctx->id("$PACKER_VCC_NET"));
+        connect_port(ctx, gnd_net, gnd_drv, id_Q);
+        connect_port(ctx, vcc_net, vcc_drv, id_Q);
+    }
+
+    CellPinState get_pin_needed_muxval(CellInfo *cell, IdString port)
+    {
+        NetInfo *net = get_net_or_empty(cell, port);
+        if (net == nullptr || net->driver.cell == nullptr) {
+            // Pin is disconnected
+            // If a mux value exists already, honour it
+            CellPinState exist_mux = cell->get_pin_state(port);
+            if (exist_mux != PIN_SIG)
+                return exist_mux;
+            // Otherwise, look up the default value and use that
+            CellPinStyle pin_style = ctx->get_cell_pin_style(cell, port);
+            if ((pin_style & PINDEF_MASK) == PINDEF_0)
+                return PIN_0;
+            else if ((pin_style & PINDEF_MASK) == PINDEF_1)
+                return PIN_1;
+            else
+                return PIN_SIG;
+        }
+        // Look to see if the driver is an inverter or constant
+        IdString drv_type = net->driver.cell->type;
+        if (drv_type == id_MISTRAL_NOT)
+            return PIN_INV;
+        else if (drv_type == id_GND)
+            return PIN_0;
+        else if (drv_type == id_VCC)
+            return PIN_1;
+        else
+            return PIN_SIG;
+    }
+
+    void uninvert_port(CellInfo *cell, IdString port)
+    {
+        // Rewire a port so it is driven by the input to an inverter
+        NetInfo *net = get_net_or_empty(cell, port);
+        NPNR_ASSERT(net != nullptr && net->driver.cell != nullptr && net->driver.cell->type == id_MISTRAL_NOT);
+        CellInfo *inv = net->driver.cell;
+        disconnect_port(ctx, cell, port);
+
+        NetInfo *inv_a = get_net_or_empty(inv, id_A);
+        if (inv_a != nullptr) {
+            connect_port(ctx, inv_a, cell, port);
+        }
+    }
+
+    void process_inv_constants(CellInfo *cell)
+    {
+        // TODO: we might need to create missing inputs here in some cases so we can tie them to the correct constant?
+        // Fold inverters and constants into a cell
+        for (auto &port : cell->ports) {
+            // Iterate over all inputs
+            if (port.second.type != PORT_IN)
+                continue;
+            IdString port_name = port.first;
+
+            CellPinState req_mux = get_pin_needed_muxval(cell, port_name);
+            if (req_mux == PIN_SIG) {
+                // No special setting required, ignore
+                continue;
+            }
+
+            CellPinStyle pin_style = ctx->get_cell_pin_style(cell, port_name);
+
+            if (req_mux == PIN_INV) {
+                // Pin is inverted. If there is a hard inverter; then use it
+                if (pin_style & PINOPT_INV) {
+                    uninvert_port(cell, port_name);
+                    cell->pin_data[port_name].state = PIN_INV;
+                }
+            } else if (req_mux == PIN_0 || req_mux == PIN_1) {
+                // Pin is tied to a constant
+                // If there is a hard constant option; use it
+                if ((pin_style & int(req_mux)) == req_mux) {
+                    disconnect_port(ctx, cell, port_name);
+                    cell->pin_data[port_name].state = req_mux;
+                } else {
+                    disconnect_port(ctx, cell, port_name);
+                    // There is no hard constant, we need to connect it to the relevant soft-constant net
+                    connect_port(ctx, (req_mux == PIN_1) ? vcc_net : gnd_net, cell, port_name);
+                }
+            }
+        }
+    }
+
+    void trim_design()
+    {
+        // Remove unused inverters and high/low drivers
+        std::vector<IdString> trim_cells;
+        std::vector<IdString> trim_nets;
+        for (auto cell : sorted(ctx->cells)) {
+            CellInfo *ci = cell.second;
+            if (ci->type != id_MISTRAL_NOT && ci->type != id_GND && ci->type != id_VCC)
+                continue;
+            IdString port = (ci->type == id_MISTRAL_NOT) ? id_Q : ci->type;
+            NetInfo *out = get_net_or_empty(ci, port);
+            if (out == nullptr) {
+                trim_cells.push_back(ci->name);
+                continue;
+            }
+            if (!out->users.empty())
+                continue;
+
+            disconnect_port(ctx, ci, id_A);
+
+            trim_cells.push_back(ci->name);
+            trim_nets.push_back(out->name);
+        }
+
+        for (IdString rem_net : trim_nets)
+            ctx->nets.erase(rem_net);
+        for (IdString rem_cell : trim_cells)
+            ctx->cells.erase(rem_cell);
+    }
+
+    void pack_constants()
+    {
+        // Iterate through cells
+        for (auto cell : sorted(ctx->cells)) {
+            CellInfo *ci = cell.second;
+            // Skip certain cells at this point
+            if (ci->type != id_MISTRAL_NOT && ci->type != id_GND && ci->type != id_VCC)
+                process_inv_constants(cell.second);
+        }
+        // Remove superfluous inverters and constant drivers
+        trim_design();
+    }
+
+    void run()
+    {
+        init_constant_nets();
+        pack_constants();
+    }
+};
+}; // namespace
 
 bool Arch::pack()
 {
     // TODO:
-    //  - Insert constant driver LUTs
-    //  - Fold constants and inverters into cell pins
     //  - Constrain IO
+
+    MistralPacker packer(getCtx());
+    packer.run();
+
     return true;
 }