Added fallback to VCC as the preferred constant if the architecture does not specify one.

Signed-off-by: Maciej Kurc <mkurc@antmicro.com>

3 files changed, 20 insertions, 6 deletions

diff --git a/fpga_interchange/arch.cc b/fpga_interchange/arch.cc
index 05b50ae2..6a7c4fe1 100644
--- a/fpga_interchange/arch.cc
+++ b/fpga_interchange/arch.cc
@@ -301,6 +301,12 @@ void Arch::init()
     for (size_t tile_type = 0; tile_type < chip_info->tile_types.size(); ++tile_type) {
         pseudo_pip_data.init_tile_type(getCtx(), tile_type);
     }
+
+    // Warn if there is no preferred constant net defined in the architecture
+    IdString const_net_name(getCtx()->chip_info->constants->best_constant_net);
+    if (const_net_name == IdString()) {
+        log_warning("The architecture does not specify preferred constant net. Using VCC as default.\n");
+    }
 }
 
 // -----------------------------------------------------------------------
@@ -877,7 +883,12 @@ static void prepare_sites_for_routing(Context *ctx)
     IdString gnd_net_name(ctx->chip_info->constants->gnd_net_name);
 
     IdString const_net_name(ctx->chip_info->constants->best_constant_net);
-    NPNR_ASSERT(const_net_name == vcc_net_name || const_net_name == gnd_net_name);
+    NPNR_ASSERT(const_net_name == IdString() || const_net_name == vcc_net_name || const_net_name == gnd_net_name);
+
+    // FIXME: Use VCC if the architecture does not device the best constant
+    if (const_net_name == IdString()) {
+        const_net_name = vcc_net_name;
+    }
 
     for (BelId bel : ctx->getBels()) {
         CellInfo *cell = ctx->getBoundBelCell(bel);
diff --git a/fpga_interchange/luts.cc b/fpga_interchange/luts.cc
index 03c01803..2a847253 100644
--- a/fpga_interchange/luts.cc
+++ b/fpga_interchange/luts.cc
@@ -429,8 +429,7 @@ bool LutMapper::remap_luts(const Context *ctx, SiteLutMappingResult *lut_mapping
                 if ((used_pins & (1 << bel_pin_idx)) == 0) {
                     NPNR_ASSERT(bel_to_cell_pin_remaps[cell_idx][bel_pin_idx] == -1);
                     cell.lutCell.pin_connections.emplace(lutBel.pins.at(bel_pin_idx), LutCell::PinConnection::Const);
-                }
-                else {
+                } else {
                     cell.lutCell.pin_connections.emplace(lutBel.pins.at(bel_pin_idx), LutCell::PinConnection::Signal);
                 }
             }
@@ -442,8 +441,7 @@ bool LutMapper::remap_luts(const Context *ctx, SiteLutMappingResult *lut_mapping
                     NPNR_ASSERT(bel_to_cell_pin_remaps[cell_idx][bel_pin_idx] == -1);
                     auto pin = lutBel.pins.at(bel_pin_idx);
                     cell.lutCell.pin_connections.emplace(pin, LutCell::PinConnection::Const);
-                }
-                else {
+                } else {
                     cell.lutCell.pin_connections.emplace(lutBel.pins.at(bel_pin_idx), LutCell::PinConnection::Signal);
                 }
             }
diff --git a/fpga_interchange/site_arch.cc b/fpga_interchange/site_arch.cc
index bb9c9a11..d0a5c48c 100644
--- a/fpga_interchange/site_arch.cc
+++ b/fpga_interchange/site_arch.cc
@@ -140,7 +140,12 @@ SiteArch::SiteArch(const SiteInformation *site_info)
     IdString gnd_net_name(ctx->chip_info->constants->gnd_net_name);
 
     IdString const_net_name(ctx->chip_info->constants->best_constant_net);
-    NPNR_ASSERT(const_net_name == vcc_net_name || const_net_name == gnd_net_name);
+    NPNR_ASSERT(const_net_name == IdString() || const_net_name == vcc_net_name || const_net_name == gnd_net_name);
+
+    // FIXME: Use VCC if the architecture does not device the best constant
+    if (const_net_name == IdString()) {
+        const_net_name = vcc_net_name;
+    }
 
     for (CellInfo *cell : site_info->cells_in_site) {
         for (const auto &pin_pair : cell->cell_bel_pins) {