ecp5: Trim IO connected to top level ports

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

1 files changed, 73 insertions, 15 deletions

diff --git a/ecp5/pack.cc b/ecp5/pack.cc
index 66428e95..ab31a8f3 100644
--- a/ecp5/pack.cc
+++ b/ecp5/pack.cc
@@ -235,6 +235,43 @@ class Ecp5Packer
         }
     }
 
+    // Return true if an port is a top level port that provides its own IOBUF
+    bool is_top_port(PortRef &port) {
+        if (port.cell == nullptr)
+            return false;
+        if (port.cell->type == id_DCUA) {
+            return port.port == id_CH0_HDINP || port.port == id_CH0_HDINN || port.port == id_CH0_HDOUTP ||
+                   port.port == id_CH0_HDOUTN ||
+                   port.port == id_CH1_HDINP || port.port == id_CH1_HDINN || port.port == id_CH1_HDOUTP ||
+                   port.port == id_CH1_HDOUTN;
+        } else if (port.cell->type == id_EXTREFB) {
+            return port.port == id_REFCLKP || port.port == id_REFCLKN;
+        } else {
+            return false;
+        }
+    }
+
+    // Return true if a net only drives a top port
+    bool drives_top_port(NetInfo *net, PortRef &tp) {
+        if (net == nullptr)
+            return false;
+        for (auto user : net->users) {
+            if (is_top_port(user)) {
+                if (net->users.size() > 1)
+                    log_error("   port %s.%s must be connected to (and only to) a top level pin\n", user.cell->name.c_str(ctx), user.port.c_str(ctx));
+                tp = user;
+                return true;
+            }
+        }
+        if (net->driver.cell != nullptr && is_top_port(net->driver)) {
+            if (net->users.size() > 1)
+                log_error("   port %s.%s must be connected to (and only to) a top level pin\n", net->driver.cell->name.c_str(ctx), net->driver.port.c_str(ctx));
+            tp = net->driver;
+            return true;
+        }
+        return false;
+    }
+
     // Simple "packer" to remove nextpnr IOBUFs, this assumes IOBUFs are manually instantiated
     void pack_io()
     {
@@ -244,10 +281,14 @@ class Ecp5Packer
             CellInfo *ci = cell.second;
             if (is_nextpnr_iob(ctx, ci)) {
                 CellInfo *trio = nullptr;
+                NetInfo *ionet = nullptr;
+                PortRef tp;
                 if (ci->type == ctx->id("$nextpnr_ibuf") || ci->type == ctx->id("$nextpnr_iobuf")) {
-                    trio = net_only_drives(ctx, ci->ports.at(ctx->id("O")).net, is_trellis_io, ctx->id("B"), true, ci);
+                    ionet = ci->ports.at(ctx->id("O")).net;
+                    trio = net_only_drives(ctx, ionet, is_trellis_io, ctx->id("B"), true, ci);
 
                 } else if (ci->type == ctx->id("$nextpnr_obuf")) {
+                    ionet = ci->ports.at(ctx->id("I")).net;
                     trio = net_only_drives(ctx, ci->ports.at(ctx->id("I")).net, is_trellis_io, ctx->id("B"), true, ci);
                 }
                 if (trio != nullptr) {
@@ -266,6 +307,20 @@ class Ecp5Packer
                             ctx->nets.erase(net2->name);
                         }
                     }
+                } else if (drives_top_port(ionet, tp)) {
+                    log_info("%s feeds %s %s.%s, removing %s %s.\n", ci->name.c_str(ctx), tp.cell->type.c_str(ctx), tp.cell->name.c_str(ctx),
+                             tp.port.c_str(ctx),
+                             ci->type.c_str(ctx), ci->name.c_str(ctx));
+                    if (ionet != nullptr) {
+                        ctx->nets.erase(ionet->name);
+                        tp.cell->ports.at(tp.port).net = nullptr;
+                    }
+                    if (ci->type == ctx->id("$nextpnr_iobuf")) {
+                        NetInfo *net2 = ci->ports.at(ctx->id("I")).net;
+                        if (net2 != nullptr) {
+                            ctx->nets.erase(net2->name);
+                        }
+                    }
                 } else {
                     // Create a TRELLIS_IO buffer
                     std::unique_ptr<CellInfo> tr_cell =
@@ -276,22 +331,25 @@ class Ecp5Packer
                 }
 
                 packed_cells.insert(ci->name);
-                for (const auto &attr : ci->attrs)
-                    trio->attrs[attr.first] = attr.second;
-
-                auto loc_attr = trio->attrs.find(ctx->id("LOC"));
-                if (loc_attr != trio->attrs.end()) {
-                    std::string pin = loc_attr->second;
-                    BelId pinBel = ctx->getPackagePinBel(pin);
-                    if (pinBel == BelId()) {
-                        log_error("IO pin '%s' constrained to pin '%s', which does not exist for package '%s'.\n",
-                                  trio->name.c_str(ctx), pin.c_str(), ctx->args.package.c_str());
-                    } else {
-                        log_info("pin '%s' constrained to Bel '%s'.\n", trio->name.c_str(ctx),
-                                 ctx->getBelName(pinBel).c_str(ctx));
+                if (trio != nullptr) {
+                    for (const auto &attr : ci->attrs)
+                        trio->attrs[attr.first] = attr.second;
+
+                    auto loc_attr = trio->attrs.find(ctx->id("LOC"));
+                    if (loc_attr != trio->attrs.end()) {
+                        std::string pin = loc_attr->second;
+                        BelId pinBel = ctx->getPackagePinBel(pin);
+                        if (pinBel == BelId()) {
+                            log_error("IO pin '%s' constrained to pin '%s', which does not exist for package '%s'.\n",
+                                      trio->name.c_str(ctx), pin.c_str(), ctx->args.package.c_str());
+                        } else {
+                            log_info("pin '%s' constrained to Bel '%s'.\n", trio->name.c_str(ctx),
+                                     ctx->getBelName(pinBel).c_str(ctx));
+                        }
+                        trio->attrs[ctx->id("BEL")] = ctx->getBelName(pinBel).str(ctx);
                     }
-                    trio->attrs[ctx->id("BEL")] = ctx->getBelName(pinBel).str(ctx);
                 }
+
             }
         }
         flush_cells();