ice40: Validity check for LVDS IO

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

1 files changed, 21 insertions, 0 deletions

diff --git a/ice40/arch_place.cc b/ice40/arch_place.cc
index a050e39f..b436f7d7 100644
--- a/ice40/arch_place.cc
+++ b/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);