ecp5: Infrastructure for FF packing

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

3 files changed, 71 insertions, 0 deletions

diff --git a/ecp5/cells.cc b/ecp5/cells.cc
index 13025da9..4beaabd2 100644
--- a/ecp5/cells.cc
+++ b/ecp5/cells.cc
@@ -18,6 +18,7 @@
  */
 
 #include "cells.h"
+#include <algorithm>
 #include "design_utils.h"
 #include "log.h"
 #include "util.h"
@@ -121,4 +122,47 @@ std::unique_ptr<CellInfo> create_ecp5_cell(Context *ctx, IdString type, std::str
     return new_cell;
 }
 
+static void set_param_safe(bool has_ff, CellInfo *lc, IdString name, const std::string &value)
+{
+    NPNR_ASSERT(!has_ff || lc->params.at(name) == value);
+    lc->params[name] = value;
+}
+
+static void replace_port_safe(bool has_ff, CellInfo *ff, IdString ff_port, CellInfo *lc, IdString lc_port)
+{
+    if (has_ff) {
+        assert(lc->ports.at(lc_port).net == ff->ports.at(ff_port).net);
+        NetInfo *ffnet = ff->ports.at(ff_port).net;
+        if (ffnet != nullptr)
+            ffnet->users.erase(
+                    std::remove_if(ffnet->users.begin(), ffnet->users.end(),
+                                   [ff, ff_port](PortRef port) { return port.cell == ff && port.port == ff_port; }),
+                    ffnet->users.end());
+    } else {
+        replace_port(ff, ff_port, lc, lc_port);
+    }
+}
+
+void ff_to_lc(Context *ctx, CellInfo *ff, CellInfo *lc, int index, bool driven_by_lut)
+{
+    bool has_ff = lc->ports.at(ctx->id("Q0")).net != nullptr || lc->ports.at(ctx->id("Q1")).net != nullptr;
+    std::string reg = "REG" + std::to_string(index);
+    set_param_safe(has_ff, lc, ctx->id("SRMODE"), str_or_default(ff->params, ctx->id("SRMODE"), "LSR_OVER_CE"));
+    set_param_safe(has_ff, lc, ctx->id("GSR"), str_or_default(ff->params, ctx->id("GSR"), "DISABLED"));
+    set_param_safe(has_ff, lc, ctx->id("CEMUX"), str_or_default(ff->params, ctx->id("CEMUX"), "1"));
+    set_param_safe(has_ff, lc, ctx->id("LSRMUX"), str_or_default(ff->params, ctx->id("LSRMUX"), "LSR"));
+    lc->params[ctx->id(reg + "_SD")] = driven_by_lut ? "1" : "0";
+    lc->params[ctx->id(reg + "_REGSET")] = str_or_default(ff->params, ctx->id("REGSET"), "RESET");
+    replace_port_safe(has_ff, ff, ctx->id("CLK"), lc, ctx->id("CLK"));
+    replace_port_safe(has_ff, ff, ctx->id("LSR"), lc, ctx->id("LSR"));
+    replace_port_safe(has_ff, ff, ctx->id("CE"), lc, ctx->id("CE"));
+
+    replace_port(ff, ctx->id("Q"), lc, ctx->id("Q" + std::to_string(index)));
+    if (driven_by_lut) {
+        replace_port(ff, ctx->id("DI"), lc, ctx->id("DI" + std::to_string(index)));
+    } else {
+        replace_port(ff, ctx->id("DI"), lc, ctx->id("M" + std::to_string(index)));
+    }
+}
+
 NEXTPNR_NAMESPACE_END
diff --git a/ecp5/cells.h b/ecp5/cells.h
index 2d11da20..d8d17061 100644
--- a/ecp5/cells.h
+++ b/ecp5/cells.h
@@ -46,6 +46,8 @@ inline bool is_pfumx(const BaseCtx *ctx, const CellInfo *cell) { return cell->ty
 
 inline bool is_l6mux(const BaseCtx *ctx, const CellInfo *cell) { return cell->type == ctx->id("L6MUX21"); }
 
+void ff_to_lc(Context *ctx, CellInfo *ff, CellInfo *lc, int index, bool driven_by_lut);
+
 NEXTPNR_NAMESPACE_END
 
 #endif
diff --git a/ecp5/pack.cc b/ecp5/pack.cc
index c44c0c4c..13b24872 100644
--- a/ecp5/pack.cc
+++ b/ecp5/pack.cc
@@ -52,6 +52,23 @@ class Ecp5Packer
         new_cells.clear();
     }
 
+    // Find FFs associated with LUTs, or LUT expansion muxes
+    void find_lutff_pairs()
+    {
+        for (auto cell : sorted(ctx->cells)) {
+            CellInfo *ci = cell.second;
+            if (is_lut(ctx, ci) || is_pfumx(ctx, ci) || is_l6mux(ctx, ci)) {
+                NetInfo *znet = ci->ports.at(ctx->id("Z")).net;
+                if (znet != nullptr) {
+                    CellInfo *ff = net_only_drives(ctx, znet, is_ff, ctx->id("DI"), false);
+                    if (ff != nullptr) {
+                        lutffPairs[ci->name] = ff->name;
+                    }
+                }
+            }
+        }
+    }
+
     // Simple "packer" to remove nextpnr IOBUFs, this assumes IOBUFs are manually instantiated
     void pack_io()
     {
@@ -126,6 +143,13 @@ class Ecp5Packer
                 replace_port(ci, ctx->id("Z"), packed.get(), ctx->id("OFX0"));
                 ctx->nets.erase(f0->name);
                 ctx->nets.erase(f1->name);
+
+                if (lutffPairs.find(ci->name) != lutffPairs.end()) {
+                    CellInfo *ff = ctx->cells.at(lutffPairs[ci->name]).get();
+                    ff_to_lc(ctx, ff, packed.get(), 0, true);
+                    packed_cells.insert(ff->name);
+                }
+
                 new_cells.push_back(std::move(packed));
                 packed_cells.insert(lc0->name);
                 packed_cells.insert(lc1->name);
@@ -157,6 +181,7 @@ class Ecp5Packer
     };
 
     std::unordered_map<IdString, SliceUsage> sliceUsage;
+    std::unordered_map<IdString, IdString> lutffPairs;
 };
 
 // Main pack function