Merge pull request #103 from YosysHQ/timingapi

Timing constraints API, multiple clock domains

18 files changed, 881 insertions, 180 deletions

diff --git a/common/nextpnr.cc b/common/nextpnr.cc
index 903ab9e4..be3bfe14 100644
--- a/common/nextpnr.cc
+++ b/common/nextpnr.cc
@@ -53,6 +53,107 @@ void IdString::initialize_add(const BaseCtx *ctx, const char *s, int idx)
     ctx->idstring_idx_to_str->push_back(&insert_rc.first->first);
 }
 
+TimingConstrObjectId BaseCtx::timingWildcardObject()
+{
+    TimingConstrObjectId id;
+    id.index = 0;
+    return id;
+}
+
+TimingConstrObjectId BaseCtx::timingClockDomainObject(NetInfo *clockDomain)
+{
+    NPNR_ASSERT(clockDomain->clkconstr != nullptr);
+    if (clockDomain->clkconstr->domain_tmg_id != TimingConstrObjectId()) {
+        return clockDomain->clkconstr->domain_tmg_id;
+    } else {
+        TimingConstraintObject obj;
+        TimingConstrObjectId id;
+        id.index = int(constraintObjects.size());
+        obj.id = id;
+        obj.type = TimingConstraintObject::CLOCK_DOMAIN;
+        obj.entity = clockDomain->name;
+        clockDomain->clkconstr->domain_tmg_id = id;
+        constraintObjects.push_back(obj);
+        return id;
+    }
+}
+
+TimingConstrObjectId BaseCtx::timingNetObject(NetInfo *net)
+{
+    if (net->tmg_id != TimingConstrObjectId()) {
+        return net->tmg_id;
+    } else {
+        TimingConstraintObject obj;
+        TimingConstrObjectId id;
+        id.index = int(constraintObjects.size());
+        obj.id = id;
+        obj.type = TimingConstraintObject::NET;
+        obj.entity = net->name;
+        constraintObjects.push_back(obj);
+        net->tmg_id = id;
+        return id;
+    }
+}
+
+TimingConstrObjectId BaseCtx::timingCellObject(CellInfo *cell)
+{
+    if (cell->tmg_id != TimingConstrObjectId()) {
+        return cell->tmg_id;
+    } else {
+        TimingConstraintObject obj;
+        TimingConstrObjectId id;
+        id.index = int(constraintObjects.size());
+        obj.id = id;
+        obj.type = TimingConstraintObject::CELL;
+        obj.entity = cell->name;
+        constraintObjects.push_back(obj);
+        cell->tmg_id = id;
+        return id;
+    }
+}
+
+TimingConstrObjectId BaseCtx::timingPortObject(CellInfo *cell, IdString port)
+{
+    if (cell->ports.at(port).tmg_id != TimingConstrObjectId()) {
+        return cell->ports.at(port).tmg_id;
+    } else {
+        TimingConstraintObject obj;
+        TimingConstrObjectId id;
+        id.index = int(constraintObjects.size());
+        obj.id = id;
+        obj.type = TimingConstraintObject::CELL_PORT;
+        obj.entity = cell->name;
+        obj.port = port;
+        constraintObjects.push_back(obj);
+        cell->ports.at(port).tmg_id = id;
+        return id;
+    }
+}
+
+void BaseCtx::addConstraint(std::unique_ptr<TimingConstraint> constr)
+{
+    for (auto fromObj : constr->from)
+        constrsFrom.emplace(fromObj, constr.get());
+    for (auto toObj : constr->to)
+        constrsTo.emplace(toObj, constr.get());
+    IdString name = constr->name;
+    constraints[name] = std::move(constr);
+}
+
+void BaseCtx::removeConstraint(IdString constrName)
+{
+    TimingConstraint *constr = constraints[constrName].get();
+    for (auto fromObj : constr->from) {
+        auto fromConstrs = constrsFrom.equal_range(fromObj);
+        constrsFrom.erase(std::find(fromConstrs.first, fromConstrs.second, std::make_pair(fromObj, constr)));
+    }
+    for (auto toObj : constr->to) {
+        auto toConstrs = constrsFrom.equal_range(toObj);
+        constrsFrom.erase(std::find(toConstrs.first, toConstrs.second, std::make_pair(toObj, constr)));
+    }
+    constraints.erase(constrName);
+}
+
 const char *BaseCtx::nameOfBel(BelId bel) const
 {
     const Context *ctx = getCtx();
@@ -306,4 +407,14 @@ void Context::check() const
     }
 }
 
+void BaseCtx::addClock(IdString net, float freq)
+{
+    log_info("constraining clock net '%s' to %.02f MHz\n", net.c_str(this), freq);
+    std::unique_ptr<ClockConstraint> cc(new ClockConstraint());
+    cc->period = getCtx()->getDelayFromNS(1000 / freq);
+    cc->high = getCtx()->getDelayFromNS(500 / freq);
+    cc->low = getCtx()->getDelayFromNS(500 / freq);
+    nets.at(net)->clkconstr = std::move(cc);
+}
+
 NEXTPNR_NAMESPACE_END
diff --git a/common/nextpnr.h b/common/nextpnr.h
index 4434c438..a6617ae4 100644
--- a/common/nextpnr.h
+++ b/common/nextpnr.h
@@ -194,6 +194,14 @@ struct Loc
     bool operator!=(const Loc &other) const { return (x != other.x) || (y != other.y) || (z != other.z); }
 };
 
+struct TimingConstrObjectId
+{
+    int32_t index = -1;
+
+    bool operator==(const TimingConstrObjectId &other) const { return index == other.index; }
+    bool operator!=(const TimingConstrObjectId &other) const { return index != other.index; }
+};
+
 NEXTPNR_NAMESPACE_END
 
 namespace std {
@@ -208,6 +216,15 @@ template <> struct hash<NEXTPNR_NAMESPACE_PREFIX Loc>
         return seed;
     }
 };
+
+template <> struct hash<NEXTPNR_NAMESPACE_PREFIX TimingConstrObjectId>
+{
+    std::size_t operator()(const NEXTPNR_NAMESPACE_PREFIX TimingConstrObjectId &obj) const noexcept
+    {
+        return hash<int>()(obj.index);
+    }
+};
+
 } // namespace std
 
 #include "archdefs.h"
@@ -266,6 +283,8 @@ struct PipMap
     PlaceStrength strength = STRENGTH_NONE;
 };
 
+struct ClockConstraint;
+
 struct NetInfo : ArchNetInfo
 {
     IdString name;
@@ -278,6 +297,10 @@ struct NetInfo : ArchNetInfo
     // wire -> uphill_pip
     std::unordered_map<WireId, PipMap> wires;
 
+    std::unique_ptr<ClockConstraint> clkconstr;
+
+    TimingConstrObjectId tmg_id;
+
     Region *region = nullptr;
 };
 
@@ -293,6 +316,7 @@ struct PortInfo
     IdString name;
     NetInfo *net;
     PortType type;
+    TimingConstrObjectId tmg_id;
 };
 
 struct CellInfo : ArchCellInfo
@@ -320,6 +344,7 @@ struct CellInfo : ArchCellInfo
     // parent.[xyz] := 0 when (constr_parent == nullptr)
 
     Region *region = nullptr;
+    TimingConstrObjectId tmg_id;
 };
 
 enum TimingPortClass
@@ -335,6 +360,68 @@ enum TimingPortClass
     TMG_IGNORE,          // Asynchronous to all clocks, "don't care", and should be ignored (false path) for analysis
 };
 
+enum ClockEdge
+{
+    RISING_EDGE,
+    FALLING_EDGE
+};
+
+struct TimingClockingInfo
+{
+    IdString clock_port; // Port name of clock domain
+    ClockEdge edge;
+    DelayInfo setup, hold; // Input timing checks
+    DelayInfo clockToQ;    // Output clock-to-Q time
+};
+
+struct ClockConstraint
+{
+    DelayInfo high;
+    DelayInfo low;
+    DelayInfo period;
+
+    TimingConstrObjectId domain_tmg_id;
+};
+
+struct TimingConstraintObject
+{
+    TimingConstrObjectId id;
+    enum
+    {
+        ANYTHING,
+        CLOCK_DOMAIN,
+        NET,
+        CELL,
+        CELL_PORT
+    } type;
+    IdString entity; // Name of clock net; net or cell
+    IdString port;   // Name of port on a cell
+};
+
+struct TimingConstraint
+{
+    IdString name;
+
+    enum
+    {
+        FALSE_PATH,
+        MIN_DELAY,
+        MAX_DELAY,
+        MULTICYCLE,
+    } type;
+
+    delay_t value;
+
+    std::unordered_set<TimingConstrObjectId> from;
+    std::unordered_set<TimingConstrObjectId> to;
+};
+
+inline bool operator==(const std::pair<const TimingConstrObjectId, TimingConstraint *> &a,
+                       const std::pair<TimingConstrObjectId, TimingConstraint *> &b)
+{
+    return a.first == b.first && a.second == b.second;
+}
+
 struct DeterministicRNG
 {
     uint64_t rngstate;
@@ -431,6 +518,11 @@ struct BaseCtx
         idstring_idx_to_str = new std::vector<const std::string *>;
         IdString::initialize_add(this, "", 0);
         IdString::initialize_arch(this);
+
+        TimingConstraintObject wildcard;
+        wildcard.id.index = 0;
+        wildcard.type = TimingConstraintObject::ANYTHING;
+        constraintObjects.push_back(wildcard);
     }
 
     ~BaseCtx()
@@ -524,6 +616,30 @@ struct BaseCtx
     void refreshUiPip(PipId pip) { pipUiReload.insert(pip); }
 
     void refreshUiGroup(GroupId group) { groupUiReload.insert(group); }
+
+    // --------------------------------------------------------------
+
+    // Timing Constraint API
+
+    // constraint name -> constraint
+    std::unordered_map<IdString, std::unique_ptr<TimingConstraint>> constraints;
+    // object ID -> object
+    std::vector<TimingConstraintObject> constraintObjects;
+    // object ID -> constraint
+    std::unordered_multimap<TimingConstrObjectId, TimingConstraint *> constrsFrom;
+    std::unordered_multimap<TimingConstrObjectId, TimingConstraint *> constrsTo;
+
+    TimingConstrObjectId timingWildcardObject();
+    TimingConstrObjectId timingClockDomainObject(NetInfo *clockDomain);
+    TimingConstrObjectId timingNetObject(NetInfo *net);
+    TimingConstrObjectId timingCellObject(CellInfo *cell);
+    TimingConstrObjectId timingPortObject(CellInfo *cell, IdString port);
+
+    void addConstraint(std::unique_ptr<TimingConstraint> constr);
+    void removeConstraint(IdString constrName);
+
+    // Intended to simplify Python API
+    void addClock(IdString net, float freq);
 };
 
 NEXTPNR_NAMESPACE_END
diff --git a/common/place_common.cc b/common/place_common.cc
index 4cb5ae11..a13a963c 100644
--- a/common/place_common.cc
+++ b/common/place_common.cc
@@ -36,8 +36,8 @@ wirelen_t get_net_metric(const Context *ctx, const NetInfo *net, MetricType type
     bool driver_gb = ctx->getBelGlobalBuf(driver_cell->bel);
     if (driver_gb)
         return 0;
-    IdString clock_port;
-    bool timing_driven = ctx->timing_driven && type == MetricType::COST && ctx->getPortTimingClass(driver_cell, net->driver.port, clock_port) != TMG_IGNORE;
+    int clock_count;
+    bool timing_driven = ctx->timing_driven && type == MetricType::COST && ctx->getPortTimingClass(driver_cell, net->driver.port, clock_count) != TMG_IGNORE;
     delay_t negative_slack = 0;
     delay_t worst_slack = std::numeric_limits<delay_t>::max();
     Loc driver_loc = ctx->getBelLocation(driver_cell->bel);
diff --git a/common/router1.cc b/common/router1.cc
index adad37e9..958c24d4 100644
--- a/common/router1.cc
+++ b/common/router1.cc
@@ -808,7 +808,7 @@ bool router1(Context *ctx, const Router1Cfg &cfg)
 #endif
 
         log_info("Checksum: 0x%08x\n", ctx->checksum());
-        timing_analysis(ctx, true /* slack_histogram */, true /* print_path */);
+        timing_analysis(ctx, true /* slack_histogram */, true /* print_fmax */, true /* print_path */);
 
         ctx->unlock();
         return true;
diff --git a/common/timing.cc b/common/timing.cc
index c5a99f54..40e4d344 100644
--- a/common/timing.cc
+++ b/common/timing.cc
@@ -22,6 +22,7 @@
 #include <algorithm>
 #include <boost/range/adaptor/reversed.hpp>
 #include <deque>
+#include <map>
 #include <unordered_map>
 #include <utility>
 #include "log.h"
@@ -29,17 +30,72 @@
 
 NEXTPNR_NAMESPACE_BEGIN
 
+namespace {
+struct ClockEvent
+{
+    IdString clock;
+    ClockEdge edge;
+
+    bool operator==(const ClockEvent &other) const { return clock == other.clock && edge == other.edge; }
+};
+
+struct ClockPair
+{
+    ClockEvent start, end;
+
+    bool operator==(const ClockPair &other) const { return start == other.start && end == other.end; }
+};
+} // namespace
+
+NEXTPNR_NAMESPACE_END
+namespace std {
+
+template <> struct hash<NEXTPNR_NAMESPACE_PREFIX ClockEvent>
+{
+    std::size_t operator()(const NEXTPNR_NAMESPACE_PREFIX ClockEvent &obj) const noexcept
+    {
+        std::size_t seed = 0;
+        boost::hash_combine(seed, hash<NEXTPNR_NAMESPACE_PREFIX IdString>()(obj.clock));
+        boost::hash_combine(seed, hash<int>()(int(obj.edge)));
+        return seed;
+    }
+};
+
+template <> struct hash<NEXTPNR_NAMESPACE_PREFIX ClockPair>
+{
+    std::size_t operator()(const NEXTPNR_NAMESPACE_PREFIX ClockPair &obj) const noexcept
+    {
+        std::size_t seed = 0;
+        boost::hash_combine(seed, hash<NEXTPNR_NAMESPACE_PREFIX ClockEvent>()(obj.start));
+        boost::hash_combine(seed, hash<NEXTPNR_NAMESPACE_PREFIX ClockEvent>()(obj.start));
+        return seed;
+    }
+};
+
+} // namespace std
+NEXTPNR_NAMESPACE_BEGIN
+
 typedef std::vector<const PortRef *> PortRefVector;
 typedef std::map<int, unsigned> DelayFrequency;
 
+struct CriticalPath
+{
+    PortRefVector ports;
+    delay_t path_delay;
+    delay_t path_period;
+};
+
+typedef std::unordered_map<ClockPair, CriticalPath> CriticalPathMap;
+
 struct Timing
 {
     Context *ctx;
     bool net_delays;
     bool update;
     delay_t min_slack;
-    PortRefVector *crit_path;
+    CriticalPathMap *crit_path;
     DelayFrequency *slack_histogram;
+    IdString async_clock;
 
     struct TimingData
     {
@@ -49,23 +105,24 @@ struct Timing
         unsigned max_path_length = 0;
         delay_t min_remaining_budget;
         bool false_startpoint = false;
+        std::unordered_map<ClockEvent, delay_t> arrival_time;
     };
 
-    Timing(Context *ctx, bool net_delays, bool update, PortRefVector *crit_path = nullptr,
+    Timing(Context *ctx, bool net_delays, bool update, CriticalPathMap *crit_path = nullptr,
            DelayFrequency *slack_histogram = nullptr)
             : ctx(ctx), net_delays(net_delays), update(update), min_slack(1.0e12 / ctx->target_freq),
-              crit_path(crit_path), slack_histogram(slack_histogram)
+              crit_path(crit_path), slack_histogram(slack_histogram), async_clock(ctx->id("$async$"))
     {
     }
 
     delay_t walk_paths()
     {
-        const auto clk_period = delay_t(1.0e12 / ctx->target_freq);
+        const auto clk_period = ctx->getDelayFromNS(1.0e9 / ctx->target_freq).maxDelay();
 
         // First, compute the topographical order of nets to walk through the circuit, assuming it is a _acyclic_ graph
         // TODO(eddieh): Handle the case where it is cyclic, e.g. combinatorial loops
         std::vector<NetInfo *> topographical_order;
-        std::unordered_map<const NetInfo *, TimingData> net_data;
+        std::unordered_map<const NetInfo *, std::unordered_map<ClockEvent, TimingData>> net_data;
         // In lieu of deleting edges from the graph, simply count the number of fanins to each output port
         std::unordered_map<const PortInfo *, unsigned> port_fanin;
 
@@ -84,22 +141,34 @@ struct Timing
             }
 
             for (auto o : output_ports) {
-                IdString clockPort;
-                TimingPortClass portClass = ctx->getPortTimingClass(cell.second.get(), o->name, clockPort);
+                int clocks = 0;
+                TimingPortClass portClass = ctx->getPortTimingClass(cell.second.get(), o->name, clocks);
                 // If output port is influenced by a clock (e.g. FF output) then add it to the ordering as a timing
                 // start-point
                 if (portClass == TMG_REGISTER_OUTPUT) {
-                    DelayInfo clkToQ;
-                    ctx->getCellDelay(cell.second.get(), clockPort, o->name, clkToQ);
                     topographical_order.emplace_back(o->net);
-                    net_data.emplace(o->net, TimingData{clkToQ.maxDelay()});
+                    for (int i = 0; i < clocks; i++) {
+                        TimingClockingInfo clkInfo = ctx->getPortClockingInfo(cell.second.get(), o->name, i);
+                        const NetInfo *clknet = get_net_or_empty(cell.second.get(), clkInfo.clock_port);
+                        IdString clksig = clknet ? clknet->name : async_clock;
+                        net_data[o->net][ClockEvent{clksig, clknet ? clkInfo.edge : RISING_EDGE}] =
+                                TimingData{clkInfo.clockToQ.maxDelay()};
+                    }
+
                 } else {
                     if (portClass == TMG_STARTPOINT || portClass == TMG_GEN_CLOCK || portClass == TMG_IGNORE) {
                         topographical_order.emplace_back(o->net);
                         TimingData td;
                         td.false_startpoint = (portClass == TMG_GEN_CLOCK || portClass == TMG_IGNORE);
-                        net_data.emplace(o->net, std::move(td));
+                        td.max_arrival = 0;
+                        net_data[o->net][ClockEvent{async_clock, RISING_EDGE}] = td;
                     }
+
+                    // Don't analyse paths from a clock input to other pins - they will be considered by the
+                    // special-case handling register input/output class ports
+                    if (portClass == TMG_CLOCK_INPUT)
+                        continue;
+
                     // Otherwise, for all driven input ports on this cell, if a timing arc exists between the input and
                     // the current output port, increment fanin counter
                     for (auto i : input_ports) {
@@ -120,14 +189,15 @@ struct Timing
             queue.pop_front();
 
             for (auto &usr : net->users) {
-                IdString clockPort;
-                TimingPortClass usrClass = ctx->getPortTimingClass(usr.cell, usr.port, clockPort);
+                int user_clocks;
+                TimingPortClass usrClass = ctx->getPortTimingClass(usr.cell, usr.port, user_clocks);
                 if (usrClass == TMG_IGNORE || usrClass == TMG_CLOCK_INPUT)
                     continue;
                 for (auto &port : usr.cell->ports) {
                     if (port.second.type != PORT_OUT || !port.second.net)
                         continue;
-                    TimingPortClass portClass = ctx->getPortTimingClass(usr.cell, port.first, clockPort);
+                    int port_clocks;
+                    TimingPortClass portClass = ctx->getPortTimingClass(usr.cell, port.first, port_clocks);
 
                     // Skip if this is a clocked output (but allow non-clocked ones)
                     if (portClass == TMG_REGISTER_OUTPUT || portClass == TMG_STARTPOINT || portClass == TMG_IGNORE ||
@@ -174,137 +244,213 @@ struct Timing
 
         // Go forwards topographically to find the maximum arrival time and max path length for each net
         for (auto net : topographical_order) {
-            auto &nd = net_data.at(net);
-            const auto net_arrival = nd.max_arrival;
-            const auto net_length_plus_one = nd.max_path_length + 1;
-            nd.min_remaining_budget = clk_period;
-            for (auto &usr : net->users) {
-                IdString clockPort;
-                TimingPortClass portClass = ctx->getPortTimingClass(usr.cell, usr.port, clockPort);
-                if (portClass == TMG_REGISTER_INPUT || portClass == TMG_ENDPOINT || portClass == TMG_IGNORE) {
-                } else {
+            if (!net_data.count(net))
+                continue;
+            auto &nd_map = net_data.at(net);
+            for (auto &startdomain : nd_map) {
+                ClockEvent start_clk = startdomain.first;
+                auto &nd = startdomain.second;
+                if (nd.false_startpoint)
+                    continue;
+                const auto net_arrival = nd.max_arrival;
+                const auto net_length_plus_one = nd.max_path_length + 1;
+                nd.min_remaining_budget = clk_period;
+                for (auto &usr : net->users) {
+                    int port_clocks;
+                    TimingPortClass portClass = ctx->getPortTimingClass(usr.cell, usr.port, port_clocks);
                     auto net_delay = net_delays ? ctx->getNetinfoRouteDelay(net, usr) : delay_t();
-                    auto budget_override = ctx->getBudgetOverride(net, usr, net_delay);
                     auto usr_arrival = net_arrival + net_delay;
-                    // Iterate over all output ports on the same cell as the sink
-                    for (auto port : usr.cell->ports) {
-                        if (port.second.type != PORT_OUT || !port.second.net)
-                            continue;
-                        DelayInfo comb_delay;
-                        // Look up delay through this path
-                        bool is_path = ctx->getCellDelay(usr.cell, usr.port, port.first, comb_delay);
-                        if (!is_path)
-                            continue;
-                        auto &data = net_data[port.second.net];
-                        auto &arrival = data.max_arrival;
-                        arrival = std::max(arrival, usr_arrival + comb_delay.maxDelay());
-                        if (!budget_override) { // Do not increment path length if budget overriden since it doesn't
-                                                // require a share of the slack
-                            auto &path_length = data.max_path_length;
-                            path_length = std::max(path_length, net_length_plus_one);
+
+                    if (portClass == TMG_REGISTER_INPUT || portClass == TMG_ENDPOINT || portClass == TMG_IGNORE ||
+                        portClass == TMG_CLOCK_INPUT) {
+                        // Skip
+                    } else {
+                        auto budget_override = ctx->getBudgetOverride(net, usr, net_delay);
+                        // Iterate over all output ports on the same cell as the sink
+                        for (auto port : usr.cell->ports) {
+                            if (port.second.type != PORT_OUT || !port.second.net)
+                                continue;
+                            DelayInfo comb_delay;
+                            // Look up delay through this path
+                            bool is_path = ctx->getCellDelay(usr.cell, usr.port, port.first, comb_delay);
+                            if (!is_path)
+                                continue;
+                            auto &data = net_data[port.second.net][start_clk];
+                            auto &arrival = data.max_arrival;
+                            arrival = std::max(arrival, usr_arrival + comb_delay.maxDelay());
+                            if (!budget_override) { // Do not increment path length if budget overriden since it doesn't
+                                // require a share of the slack
+                                auto &path_length = data.max_path_length;
+                                path_length = std::max(path_length, net_length_plus_one);
+                            }
                         }
                     }
                 }
             }
         }
 
-        const NetInfo *crit_net = nullptr;
+        std::unordered_map<ClockPair, std::pair<delay_t, NetInfo *>> crit_nets;
 
         // Now go backwards topographically to determine the minimum path slack, and to distribute all path slack evenly
         // between all nets on the path
         for (auto net : boost::adaptors::reverse(topographical_order)) {
-            auto &nd = net_data.at(net);
-            // Ignore false startpoints
-            if (nd.false_startpoint) continue;
-            const delay_t net_length_plus_one = nd.max_path_length + 1;
-            auto &net_min_remaining_budget = nd.min_remaining_budget;
-            for (auto &usr : net->users) {
-                auto net_delay = net_delays ? ctx->getNetinfoRouteDelay(net, usr) : delay_t();
-                auto budget_override = ctx->getBudgetOverride(net, usr, net_delay);
-                IdString associatedClock;
-                TimingPortClass portClass = ctx->getPortTimingClass(usr.cell, usr.port, associatedClock);
-                if (portClass == TMG_REGISTER_INPUT || portClass == TMG_ENDPOINT) {
-                    const auto net_arrival = nd.max_arrival;
-                    auto path_budget = clk_period - (net_arrival + net_delay);
-                    if (update) {
-                        auto budget_share = budget_override ? 0 : path_budget / net_length_plus_one;
-                        usr.budget = std::min(usr.budget, net_delay + budget_share);
-                        net_min_remaining_budget = std::min(net_min_remaining_budget, path_budget - budget_share);
-                    }
+            if (!net_data.count(net))
+                continue;
+            auto &nd_map = net_data.at(net);
+            for (auto &startdomain : nd_map) {
+                auto &nd = startdomain.second;
+                // Ignore false startpoints
+                if (nd.false_startpoint)
+                    continue;
+                const delay_t net_length_plus_one = nd.max_path_length + 1;
+                auto &net_min_remaining_budget = nd.min_remaining_budget;
+                for (auto &usr : net->users) {
+                    auto net_delay = net_delays ? ctx->getNetinfoRouteDelay(net, usr) : delay_t();
+                    auto budget_override = ctx->getBudgetOverride(net, usr, net_delay);
+                    int port_clocks;
+                    TimingPortClass portClass = ctx->getPortTimingClass(usr.cell, usr.port, port_clocks);
+                    if (portClass == TMG_REGISTER_INPUT || portClass == TMG_ENDPOINT) {
+                        auto process_endpoint = [&](IdString clksig, ClockEdge edge, delay_t setup) {
+                            const auto net_arrival = nd.max_arrival;
+                            const auto endpoint_arrival = net_arrival + net_delay + setup;
+                            delay_t period;
+                            // Set default period
+                            if (edge == startdomain.first.edge) {
+                                period = clk_period;
+                            } else {
+                                period = clk_period / 2;
+                            }
+                            if (clksig != async_clock) {
+                                if (ctx->nets.at(clksig)->clkconstr) {
+                                    if (edge == startdomain.first.edge) {
+                                        // same edge
+                                        period = ctx->nets.at(clksig)->clkconstr->period.minDelay();
+                                    } else if (edge == RISING_EDGE) {
+                                        // falling -> rising
+                                        period = ctx->nets.at(clksig)->clkconstr->low.minDelay();
+                                    } else if (edge == FALLING_EDGE) {
+                                        // rising -> falling
+                                        period = ctx->nets.at(clksig)->clkconstr->high.minDelay();
+                                    }
+                                }
+                            }
+                            auto path_budget = period - endpoint_arrival;
+
+                            if (update) {
+                                auto budget_share = budget_override ? 0 : path_budget / net_length_plus_one;
+                                usr.budget = std::min(usr.budget, net_delay + budget_share);
+                                net_min_remaining_budget =
+                                        std::min(net_min_remaining_budget, path_budget - budget_share);
+                            }
+
+                            if (path_budget < min_slack)
+                                min_slack = path_budget;
+
+                            if (slack_histogram) {
+                                int slack_ps = ctx->getDelayNS(path_budget) * 1000;
+                                (*slack_histogram)[slack_ps]++;
+                            }
+                            ClockEvent dest_ev{clksig, edge};
+                            ClockPair clockPair{startdomain.first, dest_ev};
+                            nd.arrival_time[dest_ev] = std::max(nd.arrival_time[dest_ev], endpoint_arrival);
+
+                            if (crit_path) {
+                                if (!crit_nets.count(clockPair) || crit_nets.at(clockPair).first < endpoint_arrival) {
+                                    crit_nets[clockPair] = std::make_pair(endpoint_arrival, net);
+                                    (*crit_path)[clockPair].path_delay = endpoint_arrival;
+                                    (*crit_path)[clockPair].path_period = period;
+                                    (*crit_path)[clockPair].ports.clear();
+                                    (*crit_path)[clockPair].ports.push_back(&usr);
+                                }
+                            }
+                        };
+                        if (portClass == TMG_REGISTER_INPUT) {
+                            for (int i = 0; i < port_clocks; i++) {
+                                TimingClockingInfo clkInfo = ctx->getPortClockingInfo(usr.cell, usr.port, i);
+                                const NetInfo *clknet = get_net_or_empty(usr.cell, clkInfo.clock_port);
+                                IdString clksig = clknet ? clknet->name : async_clock;
+                                process_endpoint(clksig, clknet ? clkInfo.edge : RISING_EDGE, clkInfo.setup.maxDelay());
+                            }
+                        } else {
+                            process_endpoint(async_clock, RISING_EDGE, 0);
+                        }
 
-                    if (path_budget < min_slack) {
-                        min_slack = path_budget;
-                        if (crit_path) {
-                            crit_path->clear();
-                            crit_path->push_back(&usr);
-                            crit_net = net;
+                    } else if (update) {
+
+                        // Iterate over all output ports on the same cell as the sink
+                        for (const auto &port : usr.cell->ports) {
+                            if (port.second.type != PORT_OUT || !port.second.net)
+                                continue;
+                            DelayInfo comb_delay;
+                            bool is_path = ctx->getCellDelay(usr.cell, usr.port, port.first, comb_delay);
+                            if (!is_path)
+                                continue;
+                            if (net_data.count(port.second.net) &&
+                                net_data.at(port.second.net).count(startdomain.first)) {
+                                auto path_budget =
+                                        net_data.at(port.second.net).at(startdomain.first).min_remaining_budget;
+                                auto budget_share = budget_override ? 0 : path_budget / net_length_plus_one;
+                                usr.budget = std::min(usr.budget, net_delay + budget_share);
+                                net_min_remaining_budget =
+                                        std::min(net_min_remaining_budget, path_budget - budget_share);
+                            }
                         }
                     }
-                    if (slack_histogram) {
-                        int slack_ps = ctx->getDelayNS(path_budget) * 1000;
-                        (*slack_histogram)[slack_ps]++;
-                    }
-                } else if (update) {
-                    // Iterate over all output ports on the same cell as the sink
-                    for (const auto &port : usr.cell->ports) {
-                        if (port.second.type != PORT_OUT || !port.second.net)
-                            continue;
-                        DelayInfo comb_delay;
-                        bool is_path = ctx->getCellDelay(usr.cell, usr.port, port.first, comb_delay);
-                        if (!is_path)
-                            continue;
-                        auto path_budget = net_data.at(port.second.net).min_remaining_budget;
-                        auto budget_share = budget_override ? 0 : path_budget / net_length_plus_one;
-                        usr.budget = std::min(usr.budget, net_delay + budget_share);
-                        net_min_remaining_budget = std::min(net_min_remaining_budget, path_budget - budget_share);
-                    }
                 }
             }
         }
 
         if (crit_path) {
             // Walk backwards from the most critical net
-            while (crit_net) {
-                const PortInfo *crit_ipin = nullptr;
-                delay_t max_arrival = std::numeric_limits<delay_t>::min();
-
-                // Look at all input ports on its driving cell
-                for (const auto &port : crit_net->driver.cell->ports) {
-                    if (port.second.type != PORT_IN || !port.second.net)
-                        continue;
-                    DelayInfo comb_delay;
-                    bool is_path =
-                            ctx->getCellDelay(crit_net->driver.cell, port.first, crit_net->driver.port, comb_delay);
-                    if (!is_path)
-                        continue;
-                    // If input port is influenced by a clock, skip
-                    IdString portClock;
-                    TimingPortClass portClass = ctx->getPortTimingClass(crit_net->driver.cell, port.first, portClock);
-                    if (portClass == TMG_REGISTER_INPUT || portClass == TMG_CLOCK_INPUT || portClass == TMG_ENDPOINT ||
-                        portClass == TMG_IGNORE)
-                        continue;
+            for (auto crit_pair : crit_nets) {
+                NetInfo *crit_net = crit_pair.second.second;
+                auto &cp_ports = (*crit_path)[crit_pair.first].ports;
+                while (crit_net) {
+                    const PortInfo *crit_ipin = nullptr;
+                    delay_t max_arrival = std::numeric_limits<delay_t>::min();
+
+                    // Look at all input ports on its driving cell
+                    for (const auto &port : crit_net->driver.cell->ports) {
+                        if (port.second.type != PORT_IN || !port.second.net)
+                            continue;
+                        DelayInfo comb_delay;
+                        bool is_path =
+                                ctx->getCellDelay(crit_net->driver.cell, port.first, crit_net->driver.port, comb_delay);
+                        if (!is_path)
+                            continue;
+                        // If input port is influenced by a clock, skip
+                        int port_clocks;
+                        TimingPortClass portClass =
+                                ctx->getPortTimingClass(crit_net->driver.cell, port.first, port_clocks);
+                        if (portClass == TMG_REGISTER_INPUT || portClass == TMG_CLOCK_INPUT ||
+                            portClass == TMG_ENDPOINT || portClass == TMG_IGNORE)
+                            continue;
 
-                    // And find the fanin net with the latest arrival time
-                    const auto net_arrival = net_data.at(port.second.net).max_arrival;
-                    if (net_arrival > max_arrival) {
-                        max_arrival = net_arrival;
-                        crit_ipin = &port.second;
+                        // And find the fanin net with the latest arrival time
+                        if (net_data.count(port.second.net) &&
+                            net_data.at(port.second.net).count(crit_pair.first.start)) {
+                            const auto net_arrival = net_data.at(port.second.net).at(crit_pair.first.start).max_arrival;
+                            if (net_arrival > max_arrival) {
+                                max_arrival = net_arrival;
+                                crit_ipin = &port.second;
+                            }
+                        }
                     }
-                }
 
-                if (!crit_ipin)
-                    break;
-
-                // Now convert PortInfo* into a PortRef*
-                for (auto &usr : crit_ipin->net->users) {
-                    if (usr.cell->name == crit_net->driver.cell->name && usr.port == crit_ipin->name) {
-                        crit_path->push_back(&usr);
+                    if (!crit_ipin)
                         break;
+
+                    // Now convert PortInfo* into a PortRef*
+                    for (auto &usr : crit_ipin->net->users) {
+                        if (usr.cell->name == crit_net->driver.cell->name && usr.port == crit_ipin->name) {
+                            cp_ports.push_back(&usr);
+                            break;
+                        }
                     }
+                    crit_net = crit_ipin->net;
                 }
-                crit_net = crit_ipin->net;
+                std::reverse(cp_ports.begin(), cp_ports.end());
             }
-            std::reverse(crit_path->begin(), crit_path->end());
         }
         return min_slack;
     }
@@ -365,30 +511,106 @@ void assign_budget(Context *ctx, bool quiet)
         log_info("Checksum: 0x%08x\n", ctx->checksum());
 }
 
-void timing_analysis(Context *ctx, bool print_histogram, bool print_path)
+void timing_analysis(Context *ctx, bool print_histogram, bool print_fmax, bool print_path)
 {
-    PortRefVector crit_path;
+    auto format_event = [ctx](const ClockEvent &e, int field_width = 0) {
+        std::string value;
+        if (e.clock == ctx->id("$async$"))
+            value = std::string("<async>");
+        else
+            value = (e.edge == FALLING_EDGE ? std::string("negedge ") : std::string("posedge ")) + e.clock.str(ctx);
+        if (int(value.length()) < field_width)
+            value.insert(value.length(), field_width - int(value.length()), ' ');
+        return value;
+    };
+
+    CriticalPathMap crit_paths;
     DelayFrequency slack_histogram;
 
-    Timing timing(ctx, true /* net_delays */, false /* update */, print_path ? &crit_path : nullptr,
+    Timing timing(ctx, true /* net_delays */, false /* update */, (print_path || print_fmax) ? &crit_paths : nullptr,
                   print_histogram ? &slack_histogram : nullptr);
-    auto min_slack = timing.walk_paths();
+    timing.walk_paths();
+    std::map<IdString, std::pair<ClockPair, CriticalPath>> clock_reports;
+    std::map<IdString, double> clock_fmax;
+    std::vector<ClockPair> xclock_paths;
+    std::set<IdString> empty_clocks; // set of clocks with no interior paths
+    if (print_path || print_fmax) {
+        for (auto path : crit_paths) {
+            const ClockEvent &a = path.first.start;
+            const ClockEvent &b = path.first.end;
+            empty_clocks.insert(a.clock);
+            empty_clocks.insert(b.clock);
+        }
+        for (auto path : crit_paths) {
+            const ClockEvent &a = path.first.start;
+            const ClockEvent &b = path.first.end;
+            if (a.clock != b.clock || a.clock == ctx->id("$async$"))
+                continue;
+            double Fmax;
+            empty_clocks.erase(a.clock);
+            if (a.edge == b.edge)
+                Fmax = 1000 / ctx->getDelayNS(path.second.path_delay);
+            else
+                Fmax = 500 / ctx->getDelayNS(path.second.path_delay);
+            if (!clock_fmax.count(a.clock) || Fmax < clock_fmax.at(a.clock)) {
+                clock_reports[a.clock] = path;
+                clock_fmax[a.clock] = Fmax;
+            }
+        }
+
+        for (auto &path : crit_paths) {
+            const ClockEvent &a = path.first.start;
+            const ClockEvent &b = path.first.end;
+            if (a.clock == b.clock && a.clock != ctx->id("$async$"))
+                continue;
+            xclock_paths.push_back(path.first);
+        }
+
+        if (clock_reports.empty()) {
+            log_warning("No clocks found in design");
+        }
+
+        std::sort(xclock_paths.begin(), xclock_paths.end(), [ctx](const ClockPair &a, const ClockPair &b) {
+            if (a.start.clock.str(ctx) < b.start.clock.str(ctx))
+                return true;
+            if (a.start.clock.str(ctx) > b.start.clock.str(ctx))
+                return false;
+            if (a.start.edge < b.start.edge)
+                return true;
+            if (a.start.edge > b.start.edge)
+                return false;
+            if (a.end.clock.str(ctx) < b.end.clock.str(ctx))
+                return true;
+            if (a.end.clock.str(ctx) > b.end.clock.str(ctx))
+                return false;
+            if (a.end.edge < b.end.edge)
+                return true;
+            return false;
+        });
+    }
 
     if (print_path) {
-        if (crit_path.empty()) {
-            log_info("Design contains no timing paths\n");
-        } else {
+        auto print_path_report = [ctx](ClockPair &clocks, PortRefVector &crit_path) {
             delay_t total = 0;
-            log_break();
-            log_info("Critical path report:\n");
-            log_info("curr total\n");
-
             auto &front = crit_path.front();
             auto &front_port = front->cell->ports.at(front->port);
             auto &front_driver = front_port.net->driver;
 
-            IdString last_port;
-            ctx->getPortTimingClass(front_driver.cell, front_driver.port, last_port);
+            int port_clocks;
+            auto portClass = ctx->getPortTimingClass(front_driver.cell, front_driver.port, port_clocks);
+            IdString last_port = front_driver.port;
+            if (portClass == TMG_REGISTER_OUTPUT) {
+                for (int i = 0; i < port_clocks; i++) {
+                    TimingClockingInfo clockInfo = ctx->getPortClockingInfo(front_driver.cell, front_driver.port, i);
+                    const NetInfo *clknet = get_net_or_empty(front_driver.cell, clockInfo.clock_port);
+                    if (clknet != nullptr && clknet->name == clocks.start.clock &&
+                        clockInfo.edge == clocks.start.edge) {
+                        last_port = clockInfo.clock_port;
+                    }
+                }
+            }
+
+            log_info("curr total\n");
             for (auto sink : crit_path) {
                 auto sink_cell = sink->cell;
                 auto &port = sink_cell->ports.at(sink->port);
@@ -396,7 +618,12 @@ void timing_analysis(Context *ctx, bool print_histogram, bool print_path)
                 auto &driver = net->driver;
                 auto driver_cell = driver.cell;
                 DelayInfo comb_delay;
-                ctx->getCellDelay(sink_cell, last_port, driver.port, comb_delay);
+                if (last_port == driver.port) {
+                    // Case where we start with a STARTPOINT etc
+                    comb_delay = ctx->getDelayFromNS(0);
+                } else {
+                    ctx->getCellDelay(sink_cell, last_port, driver.port, comb_delay);
+                }
                 total += comb_delay.maxDelay();
                 log_info("%4.1f %4.1f  Source %s.%s\n", ctx->getDelayNS(comb_delay.maxDelay()), ctx->getDelayNS(total),
                          driver_cell->name.c_str(ctx), driver.port.c_str(ctx));
@@ -427,12 +654,63 @@ void timing_analysis(Context *ctx, bool print_histogram, bool print_path)
                 }
                 last_port = sink->port;
             }
+        };
+
+        for (auto &clock : clock_reports) {
             log_break();
+            std::string start = clock.second.first.start.edge == FALLING_EDGE ? std::string("negedge") : std::string("posedge");
+            std::string end = clock.second.first.end.edge == FALLING_EDGE ? std::string("negedge") : std::string("posedge");
+            log_info("Critical path report for clock '%s' (%s -> %s):\n", clock.first.c_str(ctx), start.c_str(), end.c_str());
+            auto &crit_path = clock.second.second.ports;
+            print_path_report(clock.second.first, crit_path);
+        }
+
+        for (auto &xclock : xclock_paths) {
+            log_break();
+            std::string start = format_event(xclock.start);
+            std::string end = format_event(xclock.end);
+            log_info("Critical path report for cross-domain path '%s' -> '%s':\n", start.c_str(), end.c_str());
+            auto &crit_path = crit_paths.at(xclock).ports;
+            print_path_report(xclock, crit_path);
         }
     }
+    if (print_fmax) {
+        log_break();
+        unsigned max_width = 0;
+        for (auto &clock : clock_reports)
+            max_width = std::max<unsigned>(max_width, clock.first.str(ctx).size());
+        for (auto &clock : clock_reports) {
+            const auto &clock_name = clock.first.str(ctx);
+            const int width = max_width - clock_name.size();
+            if (ctx->nets.at(clock.first)->clkconstr) {
+                float target = 1000 / ctx->getDelayNS(ctx->nets.at(clock.first)->clkconstr->period.minDelay());
+                log_info("Max frequency for clock %*s'%s': %.02f MHz (%s at %.02f MHz)\n", width, "", clock_name.c_str(),
+                         clock_fmax[clock.first], (target < clock_fmax[clock.first]) ? "PASS" : "FAIL", target);
+            } else {
+                log_info("Max frequency for clock %*s'%s': %.02f MHz\n", width, "", clock_name.c_str(), clock_fmax[clock.first]);
+            }
+        }
+        for (auto &eclock : empty_clocks) {
+            if (eclock != ctx->id("$async$"))
+                log_info("Clock '%s' has no interior paths\n", eclock.c_str(ctx));
+        }
+        log_break();
+
+        int start_field_width = 0, end_field_width = 0;
+        for (auto &xclock : xclock_paths) {
+            start_field_width = std::max((int)format_event(xclock.start).length(), start_field_width);
+            end_field_width = std::max((int)format_event(xclock.end).length(), end_field_width);
+        }
 
-    delay_t default_slack = delay_t((1.0e9 / ctx->getDelayNS(1)) / ctx->target_freq);
-    log_info("estimated Fmax = %.2f MHz\n", 1e3 / ctx->getDelayNS(default_slack - min_slack));
+        for (auto &xclock : xclock_paths) {
+            const ClockEvent &a = xclock.start;
+            const ClockEvent &b = xclock.end;
+            auto &path = crit_paths.at(xclock);
+            auto ev_a = format_event(a, start_field_width), ev_b = format_event(b, end_field_width);
+            log_info("Max delay %s -> %s: %0.02f ns\n", ev_a.c_str(), ev_b.c_str(), ctx->getDelayNS(path.path_delay));
+        }
+        log_break();
+    }
 
     if (print_histogram && slack_histogram.size() > 0) {
         unsigned num_bins = 20;
diff --git a/common/timing.h b/common/timing.h
index cfb71ae0..1fd76310 100644
--- a/common/timing.h
+++ b/common/timing.h
@@ -29,7 +29,7 @@ void assign_budget(Context *ctx, bool quiet = false);
 
 // Perform timing analysis and print out the fmax, and optionally the
 //    critical path
-void timing_analysis(Context *ctx, bool slack_histogram = true, bool print_path = false);
+void timing_analysis(Context *ctx, bool slack_histogram = true, bool print_fmax = true, bool print_path = false);
 
 NEXTPNR_NAMESPACE_END
 
diff --git a/docs/archapi.md b/docs/archapi.md
index 40eabd9d..3c938865 100644
--- a/docs/archapi.md
+++ b/docs/archapi.md
@@ -404,6 +404,10 @@ actual penalty used is a multiple of this value (i.e. a weighted version of this
 
 Convert an `delay_t` to an actual real-world delay in nanoseconds.
 
+### DelayInfo getDelayFromNS(float v) const
+
+Convert a real-world delay in nanoseconds to a DelayInfo with equal min/max rising/falling values.
+
 ### uint32\_t getDelayChecksum(delay\_t v) const
 
 Convert a `delay_t` to an integer for checksum calculations.
@@ -461,11 +465,17 @@ Cell Delay Methods
 Returns the delay for the specified path through a cell in the `&delay` argument. The method returns
 false if there is no timing relationship from `fromPort` to `toPort`.
 
-### TimingPortClass getPortTimingClass(const CellInfo *cell, IdString port, IdString &clockPort) const
+### TimingPortClass getPortTimingClass(const CellInfo *cell, IdString port, int &clockInfoCount) const
 
 Return the _timing port class_ of a port. This can be a register or combinational input or output; clock input or
-output; general startpoint or endpoint; or a port ignored for timing purposes. For register ports, clockPort is set
-to the associated clock port.
+output; general startpoint or endpoint; or a port ignored for timing purposes. For register ports, clockInfoCount is set
+to the number of associated _clock edges_ that can be queried by getPortClockingInfo.
+
+### TimingClockingInfo getPortClockingInfo(const CellInfo *cell, IdString port, int index) const
+
+Return the _clocking info_ (including port name of clock, clock polarity and setup/hold/clock-to-out times) of a
+port. Where ports have more than one clock edge associated with them (such as DDR outputs), `index` can be used to obtain
+information for all edges. `index` must be in [0, clockInfoCount), behaviour is undefined otherwise.
 
 Placer Methods
 --------------
diff --git a/docs/constraints.md b/docs/constraints.md
new file mode 100644
index 00000000..263df7b6
--- /dev/null
+++ b/docs/constraints.md
@@ -0,0 +1,37 @@
+# Constraints
+
+There are three types of constraints available for end users of nextpnr.
+
+## Architecture-specific IO Cconstraints
+
+Architectures may provide support for their native (or any other) IO constraint format.
+The iCE40 architecture supports PCF constraints thus:
+
+    set_io led[0] 3
+
+and the ECP5 architecture supports a subset of LPF constraints:
+
+    LOCATE COMP "led[0]" SITE "E16";
+    IOBUF PORT "led[0]" IO_TYPE=LVCMOS25;
+
+
+## Absolute Placement Constraints
+
+nextpnr provides generic support for placement constraints by setting the Bel attribute on the cell to the name of
+the Bel you wish it to be placed at. For example:
+
+    (* BEL="X2/Y5/lc0" *)
+
+## Clock Constraints
+
+There are two ways to apply clock constraints in nextpnr. The `--clock {freq}` command line argument is used to
+apply a default frequency (in MHz) to all clocks without a more specific constraint.
+
+The Python API can apply clock constraints to specific named clocks. This is done by passing a Python file
+specifying these constraints to the `--pre-pack` command line argument. Inside the file, constraints are applied by
+calling the function `ctx.addClock` with the name of the clock and its frequency in MHz, for example:
+
+    ctx.addClock("csi_rx_i.dphy_clk", 96)
+    ctx.addClock("video_clk", 24)
+    ctx.addClock("uart_i.sys_clk_i", 12)
+
diff --git a/ecp5/arch.cc b/ecp5/arch.cc
index 9001ce6c..fe6a9545 100644
--- a/ecp5/arch.cc
+++ b/ecp5/arch.cc
@@ -539,10 +539,10 @@ bool Arch::getCellDelay(const CellInfo *cell, IdString fromPort, IdString toPort
             return true;
         }
 #if 0 // FIXME
-        if (fromPort == id_WCK && (toPort == id_F0 || toPort == id_F1)) {
-            delay.delay = 717;
-            return true;
-        }
+            if (fromPort == id_WCK && (toPort == id_F0 || toPort == id_F1)) {
+                delay.delay = 717;
+                return true;
+            }
 #endif
         if ((fromPort == id_A0 && toPort == id_WADO3) || (fromPort == id_A1 && toPort == id_WDO1) ||
             (fromPort == id_B0 && toPort == id_WADO1) || (fromPort == id_B1 && toPort == id_WDO3) ||
@@ -576,10 +576,10 @@ bool Arch::getCellDelay(const CellInfo *cell, IdString fromPort, IdString toPort
     }
 }
 
-TimingPortClass Arch::getPortTimingClass(const CellInfo *cell, IdString port, IdString &clockPort) const
+TimingPortClass Arch::getPortTimingClass(const CellInfo *cell, IdString port, int &clockInfoCount) const
 {
     auto disconnected = [cell](IdString p) { return !cell->ports.count(p) || cell->ports.at(p).net == nullptr; };
-
+    clockInfoCount = 0;
     if (cell->type == id_TRELLIS_SLICE) {
         int sd0 = int_or_default(cell->params, id("REG0_SD"), 0), sd1 = int_or_default(cell->params, id("REG1_SD"), 0);
         if (port == id_CLK || port == id_WCK)
@@ -598,13 +598,13 @@ TimingPortClass Arch::getPortTimingClass(const CellInfo *cell, IdString port, Id
             return TMG_COMB_OUTPUT;
         if (port == id_DI0 || port == id_DI1 || port == id_CE || port == id_LSR || (sd0 == 1 && port == id_M0) ||
             (sd1 == 1 && port == id_M1)) {
-            clockPort = id_CLK;
+            clockInfoCount = 1;
             return TMG_REGISTER_INPUT;
         }
         if (port == id_M0 || port == id_M1)
             return TMG_COMB_INPUT;
         if (port == id_Q0 || port == id_Q1) {
-            clockPort = id_CLK;
+            clockInfoCount = 1;
             return TMG_REGISTER_OUTPUT;
         }
 
@@ -614,7 +614,7 @@ TimingPortClass Arch::getPortTimingClass(const CellInfo *cell, IdString port, Id
 
         if (port == id_WD0 || port == id_WD1 || port == id_WAD0 || port == id_WAD1 || port == id_WAD2 ||
             port == id_WAD3 || port == id_WRE) {
-            clockPort = id_WCK;
+            clockInfoCount = 1;
             return TMG_REGISTER_INPUT;
         }
 
@@ -638,10 +638,8 @@ TimingPortClass Arch::getPortTimingClass(const CellInfo *cell, IdString port, Id
         for (auto c : boost::adaptors::reverse(port_name)) {
             if (std::isdigit(c))
                 continue;
-            if (c == 'A')
-                clockPort = id_CLKA;
-            else if (c == 'B')
-                clockPort = id_CLKB;
+            if (c == 'A' || c == 'B')
+                clockInfoCount = 1;
             else
                 NPNR_ASSERT_FALSE_STR("bad ram port");
             return (cell->ports.at(port).type == PORT_OUT) ? TMG_REGISTER_OUTPUT : TMG_REGISTER_INPUT;
@@ -658,6 +656,60 @@ TimingPortClass Arch::getPortTimingClass(const CellInfo *cell, IdString port, Id
     }
 }
 
+TimingClockingInfo Arch::getPortClockingInfo(const CellInfo *cell, IdString port, int index) const
+{
+    TimingClockingInfo info;
+    info.setup.delay = 0;
+    info.hold.delay = 0;
+    info.clockToQ.delay = 0;
+    if (cell->type == id_TRELLIS_SLICE) {
+        int sd0 = int_or_default(cell->params, id("REG0_SD"), 0), sd1 = int_or_default(cell->params, id("REG1_SD"), 0);
+
+        if (port == id_WD0 || port == id_WD1 || port == id_WAD0 || port == id_WAD1 || port == id_WAD2 ||
+            port == id_WAD3 || port == id_WRE) {
+            info.edge = RISING_EDGE;
+            info.clock_port = id_WCK;
+            info.setup.delay = 100;
+            info.hold.delay = 0;
+        } else if (port == id_DI0 || port == id_DI1 || port == id_CE || port == id_LSR || (sd0 == 1 && port == id_M0) ||
+                   (sd1 == 1 && port == id_M1)) {
+            info.edge = cell->sliceInfo.clkmux == id("INV") ? FALLING_EDGE : RISING_EDGE;
+            info.clock_port = id_CLK;
+            info.setup.delay = 100;
+            info.hold.delay = 0;
+        } else {
+            info.edge = cell->sliceInfo.clkmux == id("INV") ? FALLING_EDGE : RISING_EDGE;
+            info.clock_port = id_CLK;
+            info.clockToQ.delay = 395;
+        }
+    } else if (cell->type == id_DP16KD) {
+        std::string port_name = port.str(this);
+        for (auto c : boost::adaptors::reverse(port_name)) {
+            if (std::isdigit(c))
+                continue;
+            if (c == 'A') {
+                info.clock_port = id_CLKA;
+                break;
+            } else if (c == 'B') {
+                info.clock_port = id_CLKB;
+                break;
+            } else
+                NPNR_ASSERT_FALSE_STR("bad ram port " + port.str(this));
+        }
+        info.edge = (str_or_default(cell->params, info.clock_port == id_CLKB ? id("CLKBMUX") : id("CLKAMUX"), "CLK") ==
+                     "INV")
+                            ? FALLING_EDGE
+                            : RISING_EDGE;
+        if (cell->ports.at(port).type == PORT_OUT) {
+            info.clockToQ.delay = 4280;
+        } else {
+            info.setup.delay = 100;
+            info.hold.delay = 0;
+        }
+    }
+    return info;
+}
+
 std::vector<std::pair<std::string, std::string>> Arch::getTilesAtLocation(int row, int col)
 {
     std::vector<std::pair<std::string, std::string>> ret;
diff --git a/ecp5/arch.h b/ecp5/arch.h
index 9daae11d..aa3c5348 100644
--- a/ecp5/arch.h
+++ b/ecp5/arch.h
@@ -859,6 +859,12 @@ struct Arch : BaseCtx
     delay_t getDelayEpsilon() const { return 20; }
     delay_t getRipupDelayPenalty() const { return 200; }
     float getDelayNS(delay_t v) const { return v * 0.001; }
+    DelayInfo getDelayFromNS(float ns) const
+    {
+        DelayInfo del;
+        del.delay = delay_t(ns * 1000);
+        return del;
+    }
     uint32_t getDelayChecksum(delay_t v) const { return v; }
     bool getBudgetOverride(const NetInfo *net_info, const PortRef &sink, delay_t &budget) const;
 
@@ -882,8 +888,10 @@ struct Arch : BaseCtx
     // Get the delay through a cell from one port to another, returning false
     // if no path exists
     bool getCellDelay(const CellInfo *cell, IdString fromPort, IdString toPort, DelayInfo &delay) const;
-    // Get the port class, also setting clockPort if applicable
-    TimingPortClass getPortTimingClass(const CellInfo *cell, IdString port, IdString &clockPort) const;
+    // Get the port class, also setting clockInfoCount to the number of TimingClockingInfos associated with a port
+    TimingPortClass getPortTimingClass(const CellInfo *cell, IdString port, int &clockInfoCount) const;
+    // Get the TimingClockingInfo of a port
+    TimingClockingInfo getPortClockingInfo(const CellInfo *cell, IdString port, int index) const;
     // Return true if a port is a net
     bool isGlobalNet(const NetInfo *net) const;
 
diff --git a/ecp5/arch_pybindings.cc b/ecp5/arch_pybindings.cc
index 9312b4ad..5e73a673 100644
--- a/ecp5/arch_pybindings.cc
+++ b/ecp5/arch_pybindings.cc
@@ -130,6 +130,10 @@ void arch_wrap_python()
                                                                                                              "cells");
     readonly_wrapper<Context, decltype(&Context::nets), &Context::nets, wrap_context<NetMap &>>::def_wrap(ctx_cls,
                                                                                                           "nets");
+
+    fn_wrapper_2a_v<Context, decltype(&Context::addClock), &Context::addClock, conv_from_str<IdString>,
+                    pass_through<float>>::def_wrap(ctx_cls, "addClock");
+
     WRAP_RANGE(Bel, conv_to_str<BelId>);
     WRAP_RANGE(Wire, conv_to_str<WireId>);
     WRAP_RANGE(AllPip, conv_to_str<PipId>);
diff --git a/ecp5/globals.cc b/ecp5/globals.cc
index 06412fef..9b0928a4 100644
--- a/ecp5/globals.cc
+++ b/ecp5/globals.cc
@@ -350,6 +350,13 @@ class Ecp5GlobalRouter
 
         place_dcc(dcc.get());
 
+        if (net->clkconstr) {
+            glbnet->clkconstr = std::unique_ptr<ClockConstraint>(new ClockConstraint());
+            glbnet->clkconstr->low = net->clkconstr->low;
+            glbnet->clkconstr->high = net->clkconstr->high;
+            glbnet->clkconstr->period = net->clkconstr->period;
+        }
+
         ctx->cells[dcc->name] = std::move(dcc);
         NetInfo *glbptr = glbnet.get();
         ctx->nets[glbnet->name] = std::move(glbnet);
diff --git a/generic/arch.cc b/generic/arch.cc
index 4f2e07a2..77417d27 100644
--- a/generic/arch.cc
+++ b/generic/arch.cc
@@ -463,11 +463,16 @@ bool Arch::getCellDelay(const CellInfo *cell, IdString fromPort, IdString toPort
 }
 
 // Get the port class, also setting clockPort if applicable
-TimingPortClass Arch::getPortTimingClass(const CellInfo *cell, IdString port, IdString &clockPort) const
+TimingPortClass Arch::getPortTimingClass(const CellInfo *cell, IdString port, int &clockInfoCount) const
 {
     return TMG_IGNORE;
 }
 
+TimingClockingInfo Arch::getPortClockingInfo(const CellInfo *cell, IdString port, int index) const
+{
+    NPNR_ASSERT_FALSE("no clocking info for generic");
+}
+
 bool Arch::isValidBelForCell(CellInfo *cell, BelId bel) const { return true; }
 bool Arch::isBelLocationValid(BelId bel) const { return true; }
 
diff --git a/generic/arch.h b/generic/arch.h
index 9311464e..dc4258cc 100644
--- a/generic/arch.h
+++ b/generic/arch.h
@@ -211,6 +211,14 @@ struct Arch : BaseCtx
     delay_t getDelayEpsilon() const { return 0.01; }
     delay_t getRipupDelayPenalty() const { return 1.0; }
     float getDelayNS(delay_t v) const { return v; }
+
+    DelayInfo getDelayFromNS(float ns) const
+    {
+        DelayInfo del;
+        del.delay = ns;
+        return del;
+    }
+
     uint32_t getDelayChecksum(delay_t v) const { return 0; }
     bool getBudgetOverride(const NetInfo *net_info, const PortRef &sink, delay_t &budget) const;
 
@@ -225,8 +233,10 @@ struct Arch : BaseCtx
     DecalXY getGroupDecal(GroupId group) const;
 
     bool getCellDelay(const CellInfo *cell, IdString fromPort, IdString toPort, DelayInfo &delay) const;
-    // Get the port class, also setting clockPort if applicable
-    TimingPortClass getPortTimingClass(const CellInfo *cell, IdString port, IdString &clockPort) const;
+    // Get the port class, also setting clockInfoCount to the number of TimingClockingInfos associated with a port
+    TimingPortClass getPortTimingClass(const CellInfo *cell, IdString port, int &clockInfoCount) const;
+    // Get the TimingClockingInfo of a port
+    TimingClockingInfo getPortClockingInfo(const CellInfo *cell, IdString port, int index) const;
 
     bool isValidBelForCell(CellInfo *cell, BelId bel) const;
     bool isBelLocationValid(BelId bel) const;
diff --git a/ice40/arch.cc b/ice40/arch.cc
index b5e20566..2a9e167b 100644
--- a/ice40/arch.cc
+++ b/ice40/arch.cc
@@ -856,8 +856,9 @@ bool Arch::getCellDelay(const CellInfo *cell, IdString fromPort, IdString toPort
 }
 
 // Get the port class, also setting clockPort to associated clock if applicable
-TimingPortClass Arch::getPortTimingClass(const CellInfo *cell, IdString port, IdString &clockPort) const
+TimingPortClass Arch::getPortTimingClass(const CellInfo *cell, IdString port, int &clockInfoCount) const
 {
+    clockInfoCount = 0;
     if (cell->type == id_ICESTORM_LC) {
         if (port == id_CLK)
             return TMG_CLOCK_INPUT;
@@ -870,18 +871,15 @@ TimingPortClass Arch::getPortTimingClass(const CellInfo *cell, IdString port, Id
             if (cell->lcInfo.inputCount == 0)
                 return TMG_IGNORE;
             if (cell->lcInfo.dffEnable) {
-                clockPort = id_CLK;
+                clockInfoCount = 1;
                 return TMG_REGISTER_OUTPUT;
-            }
-            else
+            } else
                 return TMG_COMB_OUTPUT;
-        }
-        else {
+        } else {
             if (cell->lcInfo.dffEnable) {
-                clockPort = id_CLK;
+                clockInfoCount = 1;
                 return TMG_REGISTER_INPUT;
-            }
-            else
+            } else
                 return TMG_COMB_INPUT;
         }
     } else if (cell->type == id_ICESTORM_RAM) {
@@ -889,23 +887,22 @@ TimingPortClass Arch::getPortTimingClass(const CellInfo *cell, IdString port, Id
         if (port == id_RCLK || port == id_WCLK)
             return TMG_CLOCK_INPUT;
 
-        if (port.str(this)[0] == 'R')
-            clockPort = id_RCLK;
-        else
-            clockPort = id_WCLK;
+        clockInfoCount = 1;
 
         if (cell->ports.at(port).type == PORT_OUT)
             return TMG_REGISTER_OUTPUT;
         else
             return TMG_REGISTER_INPUT;
     } else if (cell->type == id_ICESTORM_DSP || cell->type == id_ICESTORM_SPRAM) {
-        clockPort = id_CLK;
-        if (port == id_CLK)
+        if (port == id_CLK || port == id_CLOCK)
             return TMG_CLOCK_INPUT;
-        else if (cell->ports.at(port).type == PORT_OUT)
-            return TMG_REGISTER_OUTPUT;
-        else
-            return TMG_REGISTER_INPUT;
+        else {
+            clockInfoCount = 1;
+            if (cell->ports.at(port).type == PORT_OUT)
+                return TMG_REGISTER_OUTPUT;
+            else
+                return TMG_REGISTER_INPUT;
+        }
     } else if (cell->type == id_SB_IO) {
         if (port == id_D_IN_0 || port == id_D_IN_1)
             return TMG_STARTPOINT;
@@ -934,6 +931,51 @@ TimingPortClass Arch::getPortTimingClass(const CellInfo *cell, IdString port, Id
     log_error("no timing info for port '%s' of cell type '%s'\n", port.c_str(this), cell->type.c_str(this));
 }
 
+TimingClockingInfo Arch::getPortClockingInfo(const CellInfo *cell, IdString port, int index) const
+{
+    TimingClockingInfo info;
+    if (cell->type == id_ICESTORM_LC) {
+        info.clock_port = id_CLK;
+        info.edge = cell->lcInfo.negClk ? FALLING_EDGE : RISING_EDGE;
+        if (port == id_O) {
+            bool has_clktoq = getCellDelay(cell, id_CLK, id_O, info.clockToQ);
+            NPNR_ASSERT(has_clktoq);
+        } else {
+            info.setup.delay = 100;
+            info.hold.delay = 0;
+        }
+    } else if (cell->type == id_ICESTORM_RAM) {
+        if (port.str(this)[0] == 'R') {
+            info.clock_port = id_RCLK;
+            info.edge = bool_or_default(cell->params, id("NEG_CLK_R")) ? FALLING_EDGE : RISING_EDGE;
+        } else {
+            info.clock_port = id_WCLK;
+            info.edge = bool_or_default(cell->params, id("NEG_CLK_W")) ? FALLING_EDGE : RISING_EDGE;
+        }
+        if (cell->ports.at(port).type == PORT_OUT) {
+            bool has_clktoq = getCellDelay(cell, info.clock_port, port, info.clockToQ);
+            NPNR_ASSERT(has_clktoq);
+        } else {
+            info.setup.delay = 100;
+            info.hold.delay = 0;
+        }
+    } else if (cell->type == id_ICESTORM_DSP || cell->type == id_ICESTORM_SPRAM) {
+        info.clock_port = cell->type == id_ICESTORM_SPRAM ? id_CLOCK : id_CLK;
+        info.edge = RISING_EDGE;
+        if (cell->ports.at(port).type == PORT_OUT) {
+            bool has_clktoq = getCellDelay(cell, info.clock_port, port, info.clockToQ);
+            if (!has_clktoq)
+                info.clockToQ.delay = 100;
+        } else {
+            info.setup.delay = 100;
+            info.hold.delay = 0;
+        }
+    } else {
+        NPNR_ASSERT_FALSE("unhandled cell type in getPortClockingInfo");
+    }
+    return info;
+}
+
 bool Arch::isGlobalNet(const NetInfo *net) const
 {
     if (net == nullptr)
diff --git a/ice40/arch.h b/ice40/arch.h
index f7d31b0e..836dc46e 100644
--- a/ice40/arch.h
+++ b/ice40/arch.h
@@ -796,6 +796,12 @@ struct Arch : BaseCtx
     delay_t getDelayEpsilon() const { return 20; }
     delay_t getRipupDelayPenalty() const { return 200; }
     float getDelayNS(delay_t v) const { return v * 0.001; }
+    DelayInfo getDelayFromNS(float ns) const
+    {
+        DelayInfo del;
+        del.delay = delay_t(ns * 1000);
+        return del;
+    }
     uint32_t getDelayChecksum(delay_t v) const { return v; }
     bool getBudgetOverride(const NetInfo *net_info, const PortRef &sink, delay_t &budget) const;
 
@@ -819,8 +825,10 @@ struct Arch : BaseCtx
     // Get the delay through a cell from one port to another, returning false
     // if no path exists
     bool getCellDelay(const CellInfo *cell, IdString fromPort, IdString toPort, DelayInfo &delay) const;
-    // Get the port class, also setting clockDomain if applicable
-    TimingPortClass getPortTimingClass(const CellInfo *cell, IdString port, IdString &clockDomain) const;
+    // Get the port class, also setting clockInfoCount to the number of TimingClockingInfos associated with a port
+    TimingPortClass getPortTimingClass(const CellInfo *cell, IdString port, int &clockInfoCount) const;
+    // Get the TimingClockingInfo of a port
+    TimingClockingInfo getPortClockingInfo(const CellInfo *cell, IdString port, int index) const;
     // Return true if a port is a net
     bool isGlobalNet(const NetInfo *net) const;
 
diff --git a/ice40/arch_pybindings.cc b/ice40/arch_pybindings.cc
index f1639ba6..3fafb1f6 100644
--- a/ice40/arch_pybindings.cc
+++ b/ice40/arch_pybindings.cc
@@ -140,6 +140,10 @@ void arch_wrap_python()
                                                                                                              "cells");
     readonly_wrapper<Context, decltype(&Context::nets), &Context::nets, wrap_context<NetMap &>>::def_wrap(ctx_cls,
                                                                                                           "nets");
+
+    fn_wrapper_2a_v<Context, decltype(&Context::addClock), &Context::addClock, conv_from_str<IdString>,
+                    pass_through<float>>::def_wrap(ctx_cls, "addClock");
+
     WRAP_RANGE(Bel, conv_to_str<BelId>);
     WRAP_RANGE(Wire, conv_to_str<WireId>);
     WRAP_RANGE(AllPip, conv_to_str<PipId>);
diff --git a/ice40/pack.cc b/ice40/pack.cc
index edd12f92..7a27d505 100644
--- a/ice40/pack.cc
+++ b/ice40/pack.cc
@@ -462,7 +462,8 @@ static bool is_logic_port(BaseCtx *ctx, const PortRef &port)
 
 static void insert_global(Context *ctx, NetInfo *net, bool is_reset, bool is_cen, bool is_logic)
 {
-    log_info("promoting %s%s%s%s\n", net->name.c_str(ctx), is_reset ? " [reset]" : "", is_cen ? " [cen]" : "", is_logic ? " [logic]" : "");
+    log_info("promoting %s%s%s%s\n", net->name.c_str(ctx), is_reset ? " [reset]" : "", is_cen ? " [cen]" : "",
+             is_logic ? " [logic]" : "");
 
     std::string glb_name = net->name.str(ctx) + std::string("_$glb_") + (is_reset ? "sr" : (is_cen ? "ce" : "clk"));
     std::unique_ptr<CellInfo> gb = create_ice_cell(ctx, ctx->id("SB_GB"), "$gbuf_" + glb_name);
@@ -489,6 +490,14 @@ static void insert_global(Context *ctx, NetInfo *net, bool is_reset, bool is_cen
         }
     }
     net->users = keep_users;
+
+    if (net->clkconstr) {
+        glbnet->clkconstr = std::unique_ptr<ClockConstraint>(new ClockConstraint());
+        glbnet->clkconstr->low = net->clkconstr->low;
+        glbnet->clkconstr->high = net->clkconstr->high;
+        glbnet->clkconstr->period = net->clkconstr->period;
+    }
+
     ctx->nets[glbnet->name] = std::move(glbnet);
     ctx->cells[gb->name] = std::move(gb);
 }