nexus: Add constant/inversion packing

Signed-off-by: David Shah <dave@ds0.me>

4 files changed, 78 insertions, 17 deletions

diff --git a/nexus/arch.h b/nexus/arch.h
index 4da60706..d5481bac 100644
--- a/nexus/arch.h
+++ b/nexus/arch.h
@@ -783,19 +783,21 @@ enum CellPinStyle
 
     PINGLB_MASK = 0x100,
 
-    PINBIT_GATED = 0x1000, // pin must be enabled in bitstream if used
-    PINBIT_1 = 0x2000,     // pin has an explicit bit that must be set if tied to 1
+    PINBIT_GATED = 0x1000,  // pin must be enabled in bitstream if used
+    PINBIT_1 = 0x2000,      // pin has an explicit bit that must be set if tied to 1
+    PINBIT_CIBMUX = 0x4000, // pin's CIBMUX must be floating for pin to be 1
 
     PINSTYLE_NONE = 0x0000, // default
-    PINSTYLE_CIB = 0x0012,  // 'CIB' signal, floats high but explicitly zeroed if not used
+    PINSTYLE_CIB = 0x4012,  // 'CIB' signal, floats high but explicitly zeroed if not used
     PINSTYLE_CLK = 0x0107,  // CLK type signal, invertible and defaults to disconnected
     PINSTYLE_CE = 0x0027,   // CE type signal, invertible and defaults to enabled
     PINSTYLE_LSR = 0x0017,  // LSR type signal, invertible and defaults to not reset
     PINSTYLE_DEDI = 0x0000, // dedicated signals, leave alone
-    PINSTYLE_PU = 0x0022,   // signals that float high and default high
+    PINSTYLE_PU = 0x4022,   // signals that float high and default high
+    PINSTYLE_T = 0x4027,    // PIO 'T' signal
 
     PINSTYLE_INV_PD = 0x0017, // invertible, pull down by default
-    PINSTYLE_INV_PU = 0x0027, // invertible, pull up by default
+    PINSTYLE_INV_PU = 0x4027, // invertible, pull up by default
 
     PINSTYLE_IOL_CE = 0x2027, // CE type signal, with explicit 'const-1' config bit
     PINSTYLE_GATE = 0x1011,   // gated signal that defaults to 0
diff --git a/nexus/fasm.cc b/nexus/fasm.cc
index 50b41e06..3029f4dc 100644
--- a/nexus/fasm.cc
+++ b/nexus/fasm.cc
@@ -170,7 +170,7 @@ struct NexusFasmWriter
         std::string tile = tile_name(pip.tile, tile_by_type_and_loc(pip.tile, pd.tile_type));
         std::string source_wire = escape_name(ctx->pip_src_wire_name(pip).str(ctx));
         std::string dest_wire = escape_name(ctx->pip_dst_wire_name(pip).str(ctx));
-        write_bit(stringf("%s.PIP.%s.%s", tile.c_str(), dest_wire.c_str(), source_wire.c_str()));
+        out << stringf("%s.PIP.%s.%s", tile.c_str(), dest_wire.c_str(), source_wire.c_str()) << std::endl;
     }
     // Write out all the pips corresponding to a net
     void write_net(const NetInfo *net)
@@ -184,6 +184,25 @@ struct NexusFasmWriter
             write_pip(p);
         blank();
     }
+    // Find the CIBMUX output for a signal
+    WireId find_cibmux(const CellInfo *cell, IdString pin)
+    {
+        WireId cursor = ctx->getBelPinWire(cell->bel, pin);
+        if (cursor == WireId())
+            return WireId();
+        for (int i = 0; i < 10; i++) {
+            std::string cursor_name = IdString(ctx->wire_data(cursor).name).str(ctx);
+            if (cursor_name.find("JCIBMUXOUT") == 0) {
+                return cursor;
+            }
+            for (PipId pip : ctx->getPipsUphill(cursor))
+                if (ctx->checkPipAvail(pip)) {
+                    cursor = ctx->getPipSrcWire(pip);
+                    break;
+                }
+        }
+        return WireId();
+    }
     // Write out the mux config for a cell
     void write_cell_muxes(const CellInfo *cell)
     {
@@ -206,8 +225,26 @@ struct NexusFasmWriter
             // Pins that must be explictly set to 1 rather than just left floating
             if ((pin_style & PINBIT_1) && (pin_mux == PINMUX_1))
                 write_bit(stringf("%sMUX.1", ctx->nameOf(port.first)));
+            // Handle CIB muxes - these must be set such that floating pins really are floating to VCC and not connected
+            // to another CIB signal
+            if ((pin_style & PINBIT_CIBMUX) && port.second.net == nullptr) {
+                WireId cibmuxout = find_cibmux(cell, port.first);
+                if (cibmuxout != WireId()) {
+                    write_comment(stringf("CIBMUX for unused pin %s", ctx->nameOf(port.first)));
+                    bool found = false;
+                    for (PipId pip : ctx->getPipsUphill(cibmuxout)) {
+                        if (ctx->checkPipAvail(pip) && ctx->checkWireAvail(ctx->getPipSrcWire(pip))) {
+                            write_pip(pip);
+                            found = true;
+                            break;
+                        }
+                    }
+                    NPNR_ASSERT(found);
+                }
+            }
         }
     }
+
     // Write config for an OXIDE_COMB cell
     void write_comb(const CellInfo *cell)
     {
@@ -244,10 +281,7 @@ struct NexusFasmWriter
         pop();
         write_enum(cell, "REGDDR");
         write_enum(cell, "SRMODE");
-        write_enum(cell, "CLKMUX");
-        write_enum(cell, "CEMUX");
-        write_enum(cell, "LSRMUX");
-        write_enum(cell, "GSR");
+        write_cell_muxes(cell);
         pop(2);
     }
     // Write config for an SEIO33_CORE cell
@@ -267,6 +301,7 @@ struct NexusFasmWriter
         const char *iodir = is_input ? "INPUT" : (is_output ? "OUTPUT" : "BIDIR");
         write_bit(stringf("BASE_TYPE.%s_%s", iodir, str_or_default(cell->attrs, id_IO_TYPE, "LVCMOS33").c_str()));
         write_ioattr(cell, "PULLMODE", "NONE");
+        write_cell_muxes(cell);
         pop(2);
     }
     // Write config for an SEIO18_CORE cell
@@ -287,6 +322,7 @@ struct NexusFasmWriter
         const char *iodir = is_input ? "INPUT" : (is_output ? "OUTPUT" : "BIDIR");
         write_bit(stringf("BASE_TYPE.%s_%s", iodir, str_or_default(cell->attrs, id_IO_TYPE, "LVCMOS18H").c_str()));
         write_ioattr(cell, "PULLMODE", "NONE");
+        write_cell_muxes(cell);
         pop(3);
     }
     // Write config for an OSC_CORE cell
@@ -302,6 +338,7 @@ struct NexusFasmWriter
         write_enum(cell, "LF_OUTPUT_EN");
         write_enum(cell, "DEBUG_N", "DISABLED");
         write_int_vector(stringf("HF_CLK_DIV[7:0]"), ctx->parse_lattice_param(cell, id_HF_CLK_DIV, 8, 0).intval, 8);
+        write_cell_muxes(cell);
         pop(2);
     }
     // Write out FASM for the whole design
diff --git a/nexus/pack.cc b/nexus/pack.cc
index b9472ed1..e9b4336d 100644
--- a/nexus/pack.cc
+++ b/nexus/pack.cc
@@ -321,7 +321,12 @@ struct NexusPacker
     {
         NetInfo *net = get_net_or_empty(cell, port);
         if (net == nullptr || net->driver.cell == nullptr) {
-            // Pin is disconnected, return its default value
+            // Pin is disconnected
+            // If a mux value exists already, honour it
+            CellPinMux exist_mux = ctx->get_cell_pinmux(cell, port);
+            if (exist_mux != PINMUX_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 PINMUX_0;
@@ -434,7 +439,7 @@ struct NexusPacker
 
             if (req_mux == PINMUX_INV) {
                 // Pin is inverted. If there is a hard inverter; then use it
-                if ((pin_style & PINOPT_MASK) == PINOPT_INV) {
+                if (pin_style & PINOPT_INV) {
                     uninvert_port(cell, port_name);
                     ctx->set_cell_pinmux(cell, port_name, PINMUX_INV);
                 }
@@ -624,13 +629,30 @@ struct NexusPacker
         }
     }
 
+    void pack_constants()
+    {
+        // Make sure we have high and low nets available
+        get_const_net(id_VHI);
+        get_const_net(id_VLO);
+        // Iterate through cells
+        for (auto cell : sorted(ctx->cells)) {
+            CellInfo *ci = cell.second;
+            // Skip certain cells at this point
+            if (ci->type != id_LUT4 && ci->type != id_INV && ci->type != id_VHI && ci->type != id_VLO)
+                process_inv_constants(cell.second);
+        }
+        // Remove superfluous inverters and constant drivers
+        trim_design();
+    }
+
     explicit NexusPacker(Context *ctx) : ctx(ctx) {}
 
     void operator()()
     {
+        pack_io();
         pack_ffs();
+        pack_constants();
         pack_luts();
-        pack_io();
     }
 };
 
diff --git a/nexus/pins.cc b/nexus/pins.cc
index 33015add..f9ddd5f5 100644
--- a/nexus/pins.cc
+++ b/nexus/pins.cc
@@ -48,15 +48,15 @@ static const std::unordered_map<IdString, Arch::CellPinsData> base_cell_pin_data
          }},
         {id_SEIO18_CORE,
          {
-                 {id_T, PINSTYLE_CE},
+                 {id_T, PINSTYLE_T},
                  {id_B, PINSTYLE_DEDI},
-                 {{}, PINSTYLE_INV_PU},
+                 {{}, PINSTYLE_PU},
          }},
         {id_SEIO33_CORE,
          {
-                 {id_T, PINSTYLE_CE},
+                 {id_T, PINSTYLE_T},
                  {id_B, PINSTYLE_DEDI},
-                 {{}, PINSTYLE_INV_PU},
+                 {{}, PINSTYLE_PU},
          }},
         {id_OXIDE_EBR, {{id_CLKA, PINSTYLE_CLK},    {id_CLKB, PINSTYLE_CLK},    {id_CEA, PINSTYLE_CE},
                         {id_CEB, PINSTYLE_CE},      {id_CSA0, PINSTYLE_PU},     {id_CSA1, PINSTYLE_PU},