ice40: Validity check for LVDS IO

Signed-off-by: David Shah <davey1576@gmail.com>

ice40/arch.cc

@@ -975,6 +975,8 @@ void Arch::assignCellInfo(CellInfo *cell)
             cell->lcInfo.inputCount++;
         if (get_net_or_empty(cell, id_I3))
             cell->lcInfo.inputCount++;
+    } else if (cell->type == id_SB_IO) {
+        cell->ioInfo.lvds = str_or_default(cell->params, id_IO_STANDARD, "SB_LVCMOS") == "SB_LVDS_INPUT";
     }
 }
 

ice40/arch_place.cc

@@ -139,6 +139,27 @@ bool Arch::isValidBelForCell(CellInfo *cell, BelId bel) const
                 }
             }
         }
+        Loc ioLoc = getBelLocation(bel);
+        Loc compLoc = ioLoc;
+        compLoc.z = 1 - compLoc.z;
+
+        // Check LVDS pairing
+        if (cell->ioInfo.lvds) {
+            // Check correct z and complement location is free
+            if (ioLoc.z != 0)
+                return false;
+            BelId compBel = getBelByLocation(compLoc);
+            CellInfo *compCell = getBoundBelCell(compBel);
+            if (compCell)
+                return false;
+        } else {
+            // Check LVDS IO is not placed at complement location
+            BelId compBel = getBelByLocation(compLoc);
+            CellInfo *compCell = getBoundBelCell(compBel);
+            if (compCell && compCell->ioInfo.lvds)
+                return false;
+        }
+
         return getBelPackagePin(bel) != "";
     } else if (cell->type == id_SB_GB) {
         NPNR_ASSERT(cell->ports.at(id_GLOBAL_BUFFER_OUTPUT).net != nullptr);

ice40/archdefs.h

@@ -144,6 +144,11 @@ struct ArchCellInfo
             int inputCount;
             const NetInfo *clk, *cen, *sr;
         } lcInfo;
+        struct
+        {
+            bool lvds;
+            // TODO: clk packing checks...
+        } ioInfo;
     };
 };
 

ice40/constids.inc

@@ -435,3 +435,4 @@ X(ICESTORM_SPRAM)
 X(DFF_ENABLE)
 X(CARRY_ENABLE)
 X(NEG_CLK)
+X(IO_STANDARD)