Added sequential solving support to sat_solve
authorClifford Wolf <clifford@clifford.at>
Sun, 9 Jun 2013 11:35:46 +0000 (13:35 +0200)
committerClifford Wolf <clifford@clifford.at>
Sun, 9 Jun 2013 11:35:46 +0000 (13:35 +0200)
kernel/satgen.h
passes/sat/example.ys
passes/sat/sat_solve.cc

index ee2e85d72d9cc847371add04ebe6f0acffa47aa3..ec0805bb90089dbc3a36c262491ffcd3b3468c32 100644 (file)
@@ -38,6 +38,7 @@ struct SatGen
        RTLIL::Design *design;
        SigMap *sigmap;
        std::string prefix;
+       SigPool initial_signals;
 
        SatGen(ezSAT *ez, RTLIL::Design *design, SigMap *sigmap, std::string prefix = std::string()) :
                        ez(ez), design(design), sigmap(sigmap), prefix(prefix)
@@ -51,8 +52,9 @@ struct SatGen
                this->prefix = prefix;
        }
 
-       std::vector<int> importSigSpec(RTLIL::SigSpec &sig)
+       std::vector<int> importSigSpec(RTLIL::SigSpec &sig, int timestep = -1)
        {
+               assert(timestep < 0 || timestep > 0);
                RTLIL::SigSpec s = sig;
                sigmap->apply(s);
                s.expand();
@@ -61,11 +63,14 @@ struct SatGen
                vec.reserve(s.chunks.size());
 
                for (auto &c : s.chunks)
-                       if (c.wire == NULL)
+                       if (c.wire == NULL) {
                                vec.push_back(c.data.as_bool() ? ez->TRUE : ez->FALSE);
-                       else
-                               vec.push_back(ez->literal(prefix + stringf(c.wire->width == 1 ?
-                                               "%s" : "%s [%d]", RTLIL::id2cstr(c.wire->name), c.offset)));
+                       } else {
+                               std::string name = prefix;
+                               name += timestep == -1 ? "" : stringf("@%d:", timestep);
+                               name += stringf(c.wire->width == 1 ?  "%s" : "%s [%d]", RTLIL::id2cstr(c.wire->name), c.offset);
+                               vec.push_back(ez->literal(name));
+                       }
                return vec;
        }
 
@@ -89,14 +94,14 @@ struct SatGen
                        vec_y.push_back(ez->literal());
        }
 
-       bool importCell(RTLIL::Cell *cell)
+       bool importCell(RTLIL::Cell *cell, int timestep = -1)
        {
                if (cell->type == "$_AND_" || cell->type == "$_OR_" || cell->type == "$_XOR_" ||
                                cell->type == "$and" || cell->type == "$or" || cell->type == "$xor" || cell->type == "$xnor" ||
                                cell->type == "$add" || cell->type == "$sub") {
-                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"));
-                       std::vector<int> b = importSigSpec(cell->connections.at("\\B"));
-                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"));
+                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"), timestep);
+                       std::vector<int> b = importSigSpec(cell->connections.at("\\B"), timestep);
+                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"), timestep);
                        extendSignalWidth(a, b, y, cell);
                        if (cell->type == "$and" || cell->type == "$_AND_")
                                ez->assume(ez->vec_eq(ez->vec_and(a, b), y));
@@ -114,26 +119,26 @@ struct SatGen
                }
 
                if (cell->type == "$_INV_" || cell->type == "$not") {
-                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"));
-                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"));
+                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"), timestep);
+                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"), timestep);
                        ez->assume(ez->vec_eq(ez->vec_not(a), y));
                        return true;
                }
 
                if (cell->type == "$_MUX_" || cell->type == "$mux") {
-                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"));
-                       std::vector<int> b = importSigSpec(cell->connections.at("\\B"));
-                       std::vector<int> s = importSigSpec(cell->connections.at("\\S"));
-                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"));
+                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"), timestep);
+                       std::vector<int> b = importSigSpec(cell->connections.at("\\B"), timestep);
+                       std::vector<int> s = importSigSpec(cell->connections.at("\\S"), timestep);
+                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"), timestep);
                        ez->assume(ez->vec_eq(ez->vec_ite(s.at(0), b, a), y));
                        return true;
                }
 
                if (cell->type == "$pmux" || cell->type == "$safe_pmux") {
-                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"));
-                       std::vector<int> b = importSigSpec(cell->connections.at("\\B"));
-                       std::vector<int> s = importSigSpec(cell->connections.at("\\S"));
-                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"));
+                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"), timestep);
+                       std::vector<int> b = importSigSpec(cell->connections.at("\\B"), timestep);
+                       std::vector<int> s = importSigSpec(cell->connections.at("\\S"), timestep);
+                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"), timestep);
                        std::vector<int> tmp = a;
                        for (size_t i = 0; i < s.size(); i++) {
                                std::vector<int> part_of_b(b.begin()+i*a.size(), b.begin()+(i+1)*a.size());
@@ -146,8 +151,8 @@ struct SatGen
                }
 
                if (cell->type == "$pos" || cell->type == "$neg") {
-                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"));
-                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"));
+                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"), timestep);
+                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"), timestep);
                        if (cell->type == "$pos") {
                                ez->assume(ez->vec_eq(a, y));
                        } else {
@@ -159,8 +164,8 @@ struct SatGen
 
                if (cell->type == "$reduce_and" || cell->type == "$reduce_or" || cell->type == "$reduce_xor" ||
                                cell->type == "$reduce_xnor" || cell->type == "$reduce_bool" || cell->type == "$logic_not") {
-                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"));
-                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"));
+                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"), timestep);
+                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"), timestep);
                        if (cell->type == "$reduce_and")
                                ez->SET(ez->expression(ez->OpAnd, a), y.at(0));
                        if (cell->type == "$reduce_or" || cell->type == "$reduce_bool")
@@ -177,9 +182,9 @@ struct SatGen
                }
 
                if (cell->type == "$logic_and" || cell->type == "$logic_or") {
-                       int a = ez->expression(ez->OpOr, importSigSpec(cell->connections.at("\\A")));
-                       int b = ez->expression(ez->OpOr, importSigSpec(cell->connections.at("\\B")));
-                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"));
+                       int a = ez->expression(ez->OpOr, importSigSpec(cell->connections.at("\\A"), timestep));
+                       int b = ez->expression(ez->OpOr, importSigSpec(cell->connections.at("\\B"), timestep));
+                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"), timestep);
                        if (cell->type == "$logic_and")
                                ez->SET(ez->expression(ez->OpAnd, a, b), y.at(0));
                        else
@@ -191,9 +196,9 @@ struct SatGen
 
                if (cell->type == "$lt" || cell->type == "$le" || cell->type == "$eq" || cell->type == "$ne" || cell->type == "$ge" || cell->type == "$gt") {
                        bool is_signed = cell->parameters["\\A_SIGNED"].as_bool() && cell->parameters["\\B_SIGNED"].as_bool();
-                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"));
-                       std::vector<int> b = importSigSpec(cell->connections.at("\\B"));
-                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"));
+                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"), timestep);
+                       std::vector<int> b = importSigSpec(cell->connections.at("\\B"), timestep);
+                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"), timestep);
                        extendSignalWidth(a, b, cell);
                        if (cell->type == "$lt")
                                ez->SET(is_signed ? ez->vec_lt_signed(a, b) : ez->vec_lt_unsigned(a, b), y.at(0));
@@ -213,9 +218,9 @@ struct SatGen
                }
 
                if (cell->type == "$shl" || cell->type == "$shr" || cell->type == "$sshl" || cell->type == "$sshr") {
-                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"));
-                       std::vector<int> b = importSigSpec(cell->connections.at("\\B"));
-                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"));
+                       std::vector<int> a = importSigSpec(cell->connections.at("\\A"), timestep);
+                       std::vector<int> b = importSigSpec(cell->connections.at("\\B"), timestep);
+                       std::vector<int> y = importSigSpec(cell->connections.at("\\Y"), timestep);
                        char shift_left = cell->type == "$shl" || cell->type == "$sshl";
                        bool sign_extend = cell->type == "$sshr";
                        while (y.size() < a.size())
@@ -234,7 +239,19 @@ struct SatGen
                        return true;
                }
 
+               if (timestep > 0 && (cell->type == "$dff" || cell->type == "$_DFF_N_" || cell->type == "$_DFF_P_")) {
+                       if (timestep == 1) {
+                               initial_signals.add((*sigmap)(cell->connections.at("\\Q")));
+                       } else {
+                               std::vector<int> d = importSigSpec(cell->connections.at("\\D"), timestep-1);
+                               std::vector<int> q = importSigSpec(cell->connections.at("\\Q"), timestep);
+                               ez->assume(ez->vec_eq(d, q));
+                       }
+                       return true;
+               }
+
                // Unsupported internal cell types: $mul $div $mod $pow
+               // .. and all sequential cells except $dff and $_DFF_[NP]_
                return false;
        }
 };
index 3de8c7997eb7126d67d3ad33c34a81a8d6fa6049..dd1a117f87e4cdda11ee500d1665a2d0caa7487f 100644 (file)
@@ -4,3 +4,4 @@ sat_solve -set y 1'b1 example001
 sat_solve -set y 1'b1 example002
 sat_solve -set y_sshl 8'hf0 -set y_sshr 8'hf0 -set sh 4'd3 example003
 sat_solve -set y 1'b1 example004
+sat_solve -show rst,counter -set-at 3 y 1'b1 -seq 4 example004
index bf243ae2ec3dc1844f9824f20a47d950ef13c747..8e82e4ec312adc5e4521726639034df44cb431e2 100644 (file)
@@ -130,12 +130,25 @@ struct SatSolvePass : public Pass {
                log("        show the model for the specified signal. if no -show option is\n");
                log("        passed then a set of signals to be shown is automatically selected.\n");
                log("\n");
+               log("The following options can be used to set up a sequential problem:\n");
+               log("\n");
+               log("    -seq <N>\n");
+               log("        set up a sequential problem with <N> time steps. The steps will\n");
+               log("        be numbered from 1 to N.\n");
+               log("\n");
+               log("    -set-at <N> <signal> <value>\n");
+               log("    -unset-at <N> <signal>\n");
+               log("        set or unset the specified signal to the specified value in the\n");
+               log("        given timestep. this has priority over a -set for the same signal.\n");
+               log("\n");
        }
        virtual void execute(std::vector<std::string> args, RTLIL::Design *design)
        {
                std::vector<std::pair<std::string, std::string>> sets;
+               std::map<int, std::vector<std::pair<std::string, std::string>>> sets_at;
+               std::map<int, std::vector<std::string>> unsets_at;
                std::vector<std::string> shows;
-               int loopcount = 0;
+               int loopcount = 0, seq_len = 0;
 
                log_header("Executing SAT_SOLVE pass (solving SAT problems in the circuit).\n");
 
@@ -155,6 +168,23 @@ struct SatSolvePass : public Pass {
                                sets.push_back(std::pair<std::string, std::string>(lhs, rhs));
                                continue;
                        }
+                       if (args[argidx] == "-seq" && argidx+1 < args.size()) {
+                               seq_len = atoi(args[++argidx].c_str());
+                               continue;
+                       }
+                       if (args[argidx] == "-set-at" && argidx+3 < args.size()) {
+                               int timestep = atoi(args[++argidx].c_str());
+                               std::string lhs = args[++argidx].c_str();
+                               std::string rhs = args[++argidx].c_str();
+                               sets_at[timestep].push_back(std::pair<std::string, std::string>(lhs, rhs));
+                               continue;
+                       }
+                       if (args[argidx] == "-unset-at" && argidx+2 < args.size()) {
+                               int timestep = atoi(args[++argidx].c_str());
+                               std::string lhs = args[++argidx].c_str();
+                               unsets_at[timestep].push_back(lhs);
+                               continue;
+                       }
                        if (args[argidx] == "-show" && argidx+1 < args.size()) {
                                shows.push_back(args[++argidx]);
                                continue;
@@ -186,47 +216,119 @@ struct SatSolvePass : public Pass {
                std::map<RTLIL::Cell*,RTLIL::SigSpec> show_driven;
                CellTypes ct(design);
 
-               for (auto &s : sets)
+               for (int timestep = -1; timestep <= seq_len; timestep++)
                {
-                       RTLIL::SigSpec lhs, rhs;
+                       // set timestep=-1 for non-seq problems and timestep=1:N for seq problems
+                       if ((timestep == -1 && seq_len > 0) || timestep == 0)
+                               continue;
+
+                       if (timestep > 0)
+                               log ("\nSetting up time step %d:\n", timestep);
+                       else
+                               log ("\nSetting up SAT problem:\n");
+
+                       RTLIL::SigSpec big_lhs, big_rhs;
+
+                       for (auto &s : sets)
+                       {
+                               RTLIL::SigSpec lhs, rhs;
+
+                               if (!parse_sigstr(lhs, module, s.first))
+                                       log_cmd_error("Failed to parse lhs set expression `%s'.\n", s.first.c_str());
+                               if (!parse_sigstr(rhs, module, s.second))
+                                       log_cmd_error("Failed to parse rhs set expression `%s'.\n", s.second.c_str());
+                               show_signal_pool.add(sigmap(lhs));
+                               show_signal_pool.add(sigmap(rhs));
+
+                               if (lhs.width != rhs.width)
+                                       log_cmd_error("Set expression with different lhs and rhs sizes: %s (%s, %d bits) vs. %s (%s, %d bits)\n",
+                                               s.first.c_str(), log_signal(lhs), lhs.width, s.second.c_str(), log_signal(rhs), rhs.width);
+
+                               log("Import set-constraint: %s = %s\n", log_signal(lhs), log_signal(rhs));
+                               big_lhs.remove2(lhs, &big_rhs);
+                               big_lhs.append(lhs);
+                               big_rhs.append(rhs);
+                       }
 
-                       if (!parse_sigstr(lhs, module, s.first))
-                               log_cmd_error("Failed to parse lhs set expression `%s'.\n", s.first.c_str());
-                       if (!parse_sigstr(rhs, module, s.second))
-                               log_cmd_error("Failed to parse rhs set expression `%s'.\n", s.second.c_str());
-                       show_signal_pool.add(sigmap(lhs));
-                       show_signal_pool.add(sigmap(rhs));
+                       for (auto &s : sets_at[timestep])
+                       {
+                               RTLIL::SigSpec lhs, rhs;
+
+                               if (!parse_sigstr(lhs, module, s.first))
+                                       log_cmd_error("Failed to parse lhs set expression `%s'.\n", s.first.c_str());
+                               if (!parse_sigstr(rhs, module, s.second))
+                                       log_cmd_error("Failed to parse rhs set expression `%s'.\n", s.second.c_str());
+                               show_signal_pool.add(sigmap(lhs));
+                               show_signal_pool.add(sigmap(rhs));
+
+                               if (lhs.width != rhs.width)
+                                       log_cmd_error("Set expression with different lhs and rhs sizes: %s (%s, %d bits) vs. %s (%s, %d bits)\n",
+                                               s.first.c_str(), log_signal(lhs), lhs.width, s.second.c_str(), log_signal(rhs), rhs.width);
+
+                               log("Import set-constraint for timestep: %s = %s\n", log_signal(lhs), log_signal(rhs));
+                               big_lhs.remove2(lhs, &big_rhs);
+                               big_lhs.append(lhs);
+                               big_rhs.append(rhs);
+                       }
+
+                       for (auto &s : unsets_at[timestep])
+                       {
+                               RTLIL::SigSpec lhs;
+
+                               if (!parse_sigstr(lhs, module, s))
+                                       log_cmd_error("Failed to parse lhs set expression `%s'.\n", s.c_str());
+                               show_signal_pool.add(sigmap(lhs));
 
-                       if (lhs.width != rhs.width)
-                               log_cmd_error("Set expression with different lhs and rhs sizes: %s (%s, %d bits) vs. %s (%s, %d bits)\n",
-                                       s.first.c_str(), log_signal(lhs), lhs.width, s.second.c_str(), log_signal(rhs), rhs.width);
+                               log("Import unset-constraint for timestep: %s\n", log_signal(lhs));
+                               big_lhs.remove2(lhs, &big_rhs);
+                       }
 
-                       log("Import constraint: %s = %s\n", log_signal(lhs), log_signal(rhs));
+                       log("Final constraint equation: %s = %s\n", log_signal(big_lhs), log_signal(big_rhs));
 
-                       std::vector<int> lhs_vec = satgen.importSigSpec(lhs);
-                       std::vector<int> rhs_vec = satgen.importSigSpec(rhs);
+                       std::vector<int> lhs_vec = satgen.importSigSpec(big_lhs, timestep);
+                       std::vector<int> rhs_vec = satgen.importSigSpec(big_rhs, timestep);
                        ez.assume(ez.vec_eq(lhs_vec, rhs_vec));
+
+                       int import_cell_counter = 0;
+                       for (auto &c : module->cells)
+                               if (design->selected(module, c.second) && ct.cell_known(c.second->type)) {
+                                       // log("Import cell: %s\n", RTLIL::id2cstr(c.first));
+                                       if (satgen.importCell(c.second, timestep)) {
+                                               for (auto &p : c.second->connections)
+                                                       if (ct.cell_output(c.second->type, p.first))
+                                                               show_drivers.insert(sigmap(p.second), c.second);
+                                                       else
+                                                               show_driven[c.second].append(sigmap(p.second));
+                                               import_cell_counter++;
+                                       } else
+                                               log("Warning: failed to import cell %s (type %s) to SAT database.\n", RTLIL::id2cstr(c.first), RTLIL::id2cstr(c.second->type));
+                       }
+                       log("Imported %d cells to SAT database.\n", import_cell_counter);
                }
 
-               int import_cell_counter = 0;
-               for (auto &c : module->cells)
-                       if (design->selected(module, c.second) && ct.cell_known(c.second->type)) {
-                               // log("Import cell: %s\n", RTLIL::id2cstr(c.first));
-                               if (satgen.importCell(c.second)) {
-                                       for (auto &p : c.second->connections)
-                                               if (ct.cell_output(c.second->type, p.first))
-                                                       show_drivers.insert(sigmap(p.second), c.second);
-                                               else
-                                                       show_driven[c.second].append(sigmap(p.second));
-                                       import_cell_counter++;
-                               } else
-                                       log("Warning: failed to import cell %s (type %s) to SAT database.\n", RTLIL::id2cstr(c.first), RTLIL::id2cstr(c.second->type));
+               struct ModelBlockInfo {
+                       int timestep, offset, width;
+                       std::string description;
+                       bool operator < (const ModelBlockInfo &other) const {
+                               if (timestep != other.timestep)
+                                       return timestep < other.timestep;
+                               if (description != other.description)
+                                       return description < other.description;
+                               if (offset != other.offset)
+                                       return offset < other.offset;
+                               if (width != other.width)
+                                       return width < other.width;
+                               return false;
                        }
-               log("Imported %d cells to SAT database.\n", import_cell_counter);
+               };
 
-               RTLIL::SigSpec modelSig;
                std::vector<int> modelExpressions;
                std::vector<bool> modelValues;
+               std::set<ModelBlockInfo> modelInfo;
+
+               // Add "normal" show signals for every timestep
+
+               RTLIL::SigSpec modelSig;
 
                if (shows.size() == 0) {
                        SigPool handled_signals, final_signals;
@@ -256,52 +358,100 @@ struct SatSolvePass : public Pass {
                        }
                }
 
-               modelSig.expand();
+               modelSig.sort_and_unify();
+               // log("Model signals: %s\n", log_signal(modelSig));
+
+               for (auto &c : modelSig.chunks)
+                       if (c.wire != NULL) {
+                               ModelBlockInfo info;
+                               RTLIL::SigSpec chunksig = c;
+                               info.width = chunksig.width;
+                               info.description = log_signal(chunksig);
+
+                               for (int timestep = -1; timestep <= seq_len; timestep++) {
+                                       if ((timestep == -1 && seq_len > 0) || timestep == 0)
+                                               continue;
+                                       std::vector<int> vec = satgen.importSigSpec(chunksig, timestep);
+                                       info.timestep = timestep;
+                                       info.offset = modelExpressions.size();
+                                       modelExpressions.insert(modelExpressions.end(), vec.begin(), vec.end());
+                                       modelInfo.insert(info);
+                               }
+                       }
+
+               // Add zero step signals as collected by satgen
+
+               modelSig = satgen.initial_signals.export_all();
                for (auto &c : modelSig.chunks)
                        if (c.wire != NULL) {
+                               ModelBlockInfo info;
                                RTLIL::SigSpec chunksig = c;
-                               std::vector<int> vec = satgen.importSigSpec(chunksig);
-                               log_assert(vec.size() == 1);
-                               modelExpressions.push_back(vec[0]);
+                               info.timestep = 0;
+                               info.offset = modelExpressions.size();
+                               info.width = chunksig.width;
+                               info.description = log_signal(chunksig);
+                               std::vector<int> vec = satgen.importSigSpec(chunksig, 1);
+                               modelExpressions.insert(modelExpressions.end(), vec.begin(), vec.end());
+                               modelInfo.insert(info);
                        }
 
+#if 0
+               // print CNF for debugging
+               ez.printDIMACS(stdout, true);
+#endif
+
 rerun_solver:
-               log("Solving problem with %d variables and %d clauses..\n", ez.numCnfVariables(), ez.numCnfClauses());
+               log("\nSolving problem with %d variables and %d clauses..\n", ez.numCnfVariables(), ez.numCnfClauses());
                if (ez.solve(modelExpressions, modelValues))
                {
-                       log("SAT solving finished - model found:\n\n");
+                       log("SAT solving finished - model found:\n");
+                       log("\n");
 
-                       int modelIdx = 0;
                        int maxModelName = 10;
                        int maxModelWidth = 10;
 
-                       modelSig.optimize();
-                       for (auto &c : modelSig.chunks)
-                               if (c.wire != NULL) {
-                                       maxModelName = std::max(maxModelName, int(c.wire->name.size()));
-                                       maxModelWidth = std::max(maxModelWidth, c.width);
+                       for (auto &info : modelInfo) {
+                               maxModelName = std::max(maxModelName, int(info.description.size()));
+                               maxModelWidth = std::max(maxModelWidth, info.width);
+                       }
+
+                       int last_timestep = -2;
+                       for (auto &info : modelInfo)
+                       {
+                               RTLIL::Const value;
+                               for (int i = 0; i < info.width; i++)
+                                       value.bits.push_back(modelValues.at(info.offset+i) ? RTLIL::State::S1 : RTLIL::State::S0);
+
+                               if (info.timestep != last_timestep) {
+                                       const char *hline = "--------------------------------------------------------";
+                                       if (last_timestep == -2) {
+                                               log(seq_len > 0 ? "  Time " : "  ");
+                                               log("%-*s %10s %10s %*s\n", maxModelName+10, "Signal Name", "Dec", "Hex", maxModelWidth+5, "Bin");
+                                       }
+                                       log(seq_len > 0 ? "  ---- " : "  ");
+                                       log("%*.*s %10.10s %10.10s %*.*s\n", maxModelName+10, maxModelName+10,
+                                                       hline, hline, hline, maxModelWidth+5, maxModelWidth+5, hline);
+                                       last_timestep = info.timestep;
                                }
 
-                       const char *hline = "--------------------------------------------------------";
-                       log("  %-*s %10s %10s %*s\n", maxModelName+10, "Signal Name", "Dec", "Hex", maxModelWidth+5, "Bin");
-                       log("  %*.*s %10.10s %10.10s %*.*s\n", maxModelName+10, maxModelName+10,
-                                       hline, hline, hline, maxModelWidth+5, maxModelWidth+5, hline);
+                               if (seq_len > 0) {
+                                       if (info.timestep > 0)
+                                               log("  %4d ", info.timestep);
+                                       else
+                                               log("  init ");
+                               } else
+                                       log("  ");
 
-                       for (auto &c : modelSig.chunks) {
-                               if (c.wire == NULL)
-                                       continue;
-                               RTLIL::Const value;
-                               for (int i = 0; i < c.width; i++)
-                                       value.bits.push_back(modelValues.at(modelIdx+i) ? RTLIL::State::S1 : RTLIL::State::S0);
-                               if (c.width <= 32)
-                                       log("  %-*s %10d %10x %*s\n", maxModelName+10, log_signal(c), value.as_int(), value.as_int(), maxModelWidth+5, value.as_string().c_str());
+                               if (info.width <= 32)
+                                       log("%-*s %10d %10x %*s\n", maxModelName+10, info.description.c_str(), value.as_int(), value.as_int(), maxModelWidth+5, value.as_string().c_str());
                                else
-                                       log("  %-*s %10s %10s %*s\n", maxModelName+10, log_signal(c), "--", "--", maxModelWidth+5, value.as_string().c_str());
-                               modelIdx += c.width;
+                                       log("%-*s %10s %10s %*s\n", maxModelName+10, info.description.c_str(), "--", "--", maxModelWidth+5, value.as_string().c_str());
                        }
 
+                       if (last_timestep == -2)
+                               log("  no model variables selected for display.\n");
+
                        if (loopcount != 0) {
-                               log("\n");
                                std::vector<int> clause;
                                for (size_t i = 0; i < modelExpressions.size(); i++)
                                        clause.push_back(modelValues.at(i) ? ez.NOT(modelExpressions.at(i)) : modelExpressions.at(i));