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OpenSTA/search/ClkSkew.cc

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// OpenSTA, Static Timing Analyzer
// Copyright (c) 2025, Parallax Software, Inc.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.
//
// The origin of this software must not be misrepresented; you must not
// claim that you wrote the original software.
//
// Altered source versions must be plainly marked as such, and must not be
// misrepresented as being the original software.
//
// This notice may not be removed or altered from any source distribution.
#include "ClkSkew.hh"
#include <cmath> // abs
#include <algorithm>
#include "Fuzzy.hh"
#include "Report.hh"
#include "Debug.hh"
#include "DispatchQueue.hh"
#include "Units.hh"
#include "TimingArc.hh"
#include "Liberty.hh"
#include "Network.hh"
#include "Graph.hh"
#include "Sdc.hh"
#include "Bfs.hh"
#include "Path.hh"
#include "StaState.hh"
#include "PathAnalysisPt.hh"
#include "SearchPred.hh"
#include "Search.hh"
#include "Crpr.hh"
#include "PathEnd.hh"
namespace sta {
using std::abs;
// Source/target clock skew.
class ClkSkew
{
public:
ClkSkew();
ClkSkew(Path *src_path,
Path *tgt_path,
bool include_internal_latency,
StaState *sta);
ClkSkew(const ClkSkew &clk_skew);
void operator=(const ClkSkew &clk_skew);
Path *srcPath() { return src_path_; }
Path *tgtPath() { return tgt_path_; }
float srcLatency(const StaState *sta);
float tgtLatency(const StaState *sta);
float srcInternalClkLatency(const StaState *sta);
float tgtInternalClkLatency(const StaState *sta);
Crpr crpr(const StaState *sta);
float uncertainty(const StaState *sta);
float skew() const { return skew_; }
static bool srcTgtPathNameLess(ClkSkew &clk_skew1,
ClkSkew &clk_skew2,
const StaState *sta);
private:
float clkTreeDelay(Path *clk_path,
const StaState *sta);
Path *src_path_;
Path *tgt_path_;
bool include_internal_latency_;
float skew_;
};
ClkSkew::ClkSkew() :
src_path_(nullptr),
tgt_path_(nullptr),
include_internal_latency_(false),
skew_(0.0)
{
}
ClkSkew::ClkSkew(Path *src_path,
Path *tgt_path,
bool include_internal_latency,
StaState *sta) :
src_path_(src_path),
tgt_path_(tgt_path),
include_internal_latency_(include_internal_latency)
{
skew_ = srcLatency(sta)
- tgtLatency(sta)
- delayAsFloat(crpr(sta))
+ uncertainty(sta);
}
ClkSkew::ClkSkew(const ClkSkew &clk_skew)
{
src_path_ = clk_skew.src_path_;
tgt_path_ = clk_skew.tgt_path_;
include_internal_latency_ = clk_skew.include_internal_latency_;
skew_ = clk_skew.skew_;
}
void
ClkSkew::operator=(const ClkSkew &clk_skew)
{
src_path_ = clk_skew.src_path_;
tgt_path_ = clk_skew.tgt_path_;
include_internal_latency_ = clk_skew.include_internal_latency_;
skew_ = clk_skew.skew_;
}
float
ClkSkew::srcLatency(const StaState *sta)
{
Arrival src_arrival = src_path_->arrival();
return delayAsFloat(src_arrival) - src_path_->clkEdge(sta)->time()
+ clkTreeDelay(src_path_, sta);
}
float
ClkSkew::srcInternalClkLatency(const StaState *sta)
{
return clkTreeDelay(src_path_, sta);
}
float
ClkSkew::tgtLatency(const StaState *sta)
{
Arrival tgt_arrival = tgt_path_->arrival();
return delayAsFloat(tgt_arrival) - tgt_path_->clkEdge(sta)->time()
+ clkTreeDelay(tgt_path_, sta);
}
float
ClkSkew::tgtInternalClkLatency(const StaState *sta)
{
return clkTreeDelay(tgt_path_, sta);
}
float
ClkSkew::clkTreeDelay(Path *clk_path,
const StaState *sta)
{
if (include_internal_latency_) {
const Vertex *vertex = clk_path->vertex(sta);
const Pin *pin = vertex->pin();
const LibertyPort *port = sta->network()->libertyPort(pin);
const MinMax *min_max = clk_path->minMax(sta);
const RiseFall *rf = clk_path->transition(sta);
float slew = delayAsFloat(clk_path->slew(sta));
return port->clkTreeDelay(slew, rf, min_max);
}
else
return 0.0;
}
Crpr
ClkSkew::crpr(const StaState *sta)
{
CheckCrpr *check_crpr = sta->search()->checkCrpr();
return check_crpr->checkCrpr(src_path_, tgt_path_);
}
float
ClkSkew::uncertainty(const StaState *sta)
{
const TimingRole *check_role = (src_path_->minMax(sta) == SetupHold::max())
? TimingRole::setup()
: TimingRole::hold();
// Uncertainty decreases slack, but increases skew.
return -PathEnd::checkTgtClkUncertainty(tgt_path_, tgt_path_->clkEdge(sta),
check_role, sta);
}
bool
ClkSkew::srcTgtPathNameLess(ClkSkew &clk_skew1,
ClkSkew &clk_skew2,
const StaState *sta)
{
Network *network = sta->sdcNetwork();
const char *src_path1 = network->pathName(clk_skew1.srcPath()->pin(sta));
const char *src_path2 = network->pathName(clk_skew2.srcPath()->pin(sta));
const char *tgt_path1 = network->pathName(clk_skew1.tgtPath()->pin(sta));
const char *tgt_path2 = network->pathName(clk_skew2.tgtPath()->pin(sta));
return stringLess(src_path1, src_path2)
|| (stringEqual(src_path1, src_path2)
&& stringEqual(tgt_path1, tgt_path2));
}
////////////////////////////////////////////////////////////////
ClkSkews::ClkSkews(StaState *sta) :
StaState(sta),
fanout_pred_(sta)
{
}
void
ClkSkews::reportClkSkew(ConstClockSeq &clks,
const Corner *corner,
const SetupHold *setup_hold,
bool include_internal_latency,
int digits)
{
ClkSkewMap skews = findClkSkew(clks, corner, setup_hold,
include_internal_latency);
// Sort the clocks to report in a stable order.
ConstClockSeq sorted_clks;
for (const Clock *clk : clks)
sorted_clks.push_back(clk);
std::sort(sorted_clks.begin(), sorted_clks.end(), ClkNameLess());
for (const Clock *clk : sorted_clks) {
report_->reportLine("Clock %s", clk->name());
auto skew_itr = skews.find(clk);
if (skew_itr != skews.end())
reportClkSkew(skew_itr->second, digits);
else
report_->reportLine("No launch/capture paths found.");
report_->reportBlankLine();
}
}
void
ClkSkews::reportClkSkew(ClkSkew &clk_skew,
int digits)
{
Unit *time_unit = units_->timeUnit();
Path *src_path = clk_skew.srcPath();
Path *tgt_path = clk_skew.tgtPath();
float src_latency = clk_skew.srcLatency(this);
float tgt_latency = clk_skew.tgtLatency(this);
float src_internal_clk_latency = clk_skew.srcInternalClkLatency(this);
float tgt_internal_clk_latency = clk_skew.tgtInternalClkLatency(this);
float uncertainty = clk_skew.uncertainty(this);
if (src_internal_clk_latency != 0.0)
src_latency -= src_internal_clk_latency;
report_->reportLine("%7s source latency %s %s",
time_unit->asString(src_latency, digits),
sdc_network_->pathName(src_path->pin(this)),
src_path->transition(this)->to_string().c_str());
if (src_internal_clk_latency != 0.0)
report_->reportLine("%7s source internal clock delay",
time_unit->asString(src_internal_clk_latency, digits));
if (tgt_internal_clk_latency != 0.0)
tgt_latency -= tgt_internal_clk_latency;
report_->reportLine("%7s target latency %s %s",
time_unit->asString(-tgt_latency, digits),
sdc_network_->pathName(tgt_path->pin(this)),
tgt_path->transition(this)->to_string().c_str());
if (tgt_internal_clk_latency != 0.0)
report_->reportLine("%7s target internal clock delay",
time_unit->asString(-tgt_internal_clk_latency, digits));
if (uncertainty != 0.0)
report_->reportLine("%7s clock uncertainty",
time_unit->asString(uncertainty, digits));
report_->reportLine("%7s CRPR",
time_unit->asString(delayAsFloat(-clk_skew.crpr(this)),
digits));
report_->reportLine("--------------");
report_->reportLine("%7s %s skew",
time_unit->asString(clk_skew.skew(), digits),
src_path->minMax(this) == MinMax::max() ? "setup" : "hold");
}
float
ClkSkews::findWorstClkSkew(const Corner *corner,
const SetupHold *setup_hold,
bool include_internal_latency)
{
ConstClockSeq clks;
for (const Clock *clk : *sdc_->clocks())
clks.push_back(clk);
ClkSkewMap skews = findClkSkew(clks, corner, setup_hold, include_internal_latency);
float worst_skew = 0.0;
for (const auto& [clk, clk_skew] : skews) {
float skew = clk_skew.skew();
if (abs(skew) > abs(worst_skew))
worst_skew = skew;
}
return worst_skew;
}
ClkSkewMap
ClkSkews::findClkSkew(ConstClockSeq &clks,
const Corner *corner,
const SetupHold *setup_hold,
bool include_internal_latency)
{
ClkSkewMap skews;
corner_ = corner;
setup_hold_ = setup_hold;
include_internal_latency_ = include_internal_latency;
clk_set_.clear();
for (const Clock *clk : clks)
clk_set_.insert(clk);
if (thread_count_ > 1) {
std::vector<ClkSkewMap> partial_skews(thread_count_, skews);
for (Vertex *src_vertex : *graph_->regClkVertices()) {
if (hasClkPaths(src_vertex)) {
dispatch_queue_->dispatch([this, src_vertex, &partial_skews](int i) {
findClkSkewFrom(src_vertex, partial_skews[i]);
});
}
}
dispatch_queue_->finishTasks();
// Reduce skews from each register source.
for (size_t i = 0; i < partial_skews.size(); i++) {
for (auto& [clk, partial_skew] : partial_skews[i]) {
auto ins = skews.insert(std::make_pair(clk, partial_skew));
if (!ins.second) {
ClkSkew &final_skew = ins.first->second;
if (abs(partial_skew.skew()) > abs(final_skew.skew())
|| (fuzzyEqual(abs(partial_skew.skew()), abs(final_skew.skew()))
// Break ties based on source/target path names.
&& ClkSkew::srcTgtPathNameLess(partial_skew, final_skew, this)))
final_skew = partial_skew;
}
}
}
}
else {
for (Vertex *src_vertex : *graph_->regClkVertices()) {
if (hasClkPaths(src_vertex))
findClkSkewFrom(src_vertex, skews);
}
}
return skews;
}
bool
ClkSkews::hasClkPaths(Vertex *vertex)
{
VertexPathIterator path_iter(vertex, this);
while (path_iter.hasNext()) {
Path *path = path_iter.next();
const Clock *path_clk = path->clock(this);
if (clk_set_.find(path_clk) != clk_set_.end())
return true;
}
return false;
}
void
ClkSkews::findClkSkewFrom(Vertex *src_vertex,
ClkSkewMap &skews)
{
VertexOutEdgeIterator edge_iter(src_vertex, graph_);
while (edge_iter.hasNext()) {
Edge *edge = edge_iter.next();
if (edge->role()->genericRole() == TimingRole::regClkToQ()) {
Vertex *q_vertex = edge->to(graph_);
const RiseFall *rf = edge->timingArcSet()->isRisingFallingEdge();
const RiseFallBoth *src_rf = rf
? rf->asRiseFallBoth()
: RiseFallBoth::riseFall();
findClkSkewFrom(src_vertex, q_vertex, src_rf, skews);
}
}
}
void
ClkSkews::findClkSkewFrom(Vertex *src_vertex,
Vertex *q_vertex,
const RiseFallBoth *src_rf,
ClkSkewMap &skews)
{
VertexSet endpoints = findFanout(q_vertex);
for (Vertex *end : endpoints) {
VertexInEdgeIterator edge_iter(end, graph_);
while (edge_iter.hasNext()) {
Edge *edge = edge_iter.next();
const TimingRole *role = edge->role();
if (role->isTimingCheck()
&& ((setup_hold_ == SetupHold::max()
&& role->genericRole() == TimingRole::setup())
|| ((setup_hold_ == SetupHold::min()
&& role->genericRole() == TimingRole::hold())))) {
Vertex *tgt_vertex = edge->from(graph_);
const RiseFall *tgt_rf1 = edge->timingArcSet()->isRisingFallingEdge();
const RiseFallBoth *tgt_rf = tgt_rf1
? tgt_rf1->asRiseFallBoth()
: RiseFallBoth::riseFall();
findClkSkew(src_vertex, src_rf, tgt_vertex, tgt_rf, skews);
}
}
}
}
void
ClkSkews::findClkSkew(Vertex *src_vertex,
const RiseFallBoth *src_rf,
Vertex *tgt_vertex,
const RiseFallBoth *tgt_rf,
ClkSkewMap &skews)
{
Unit *time_unit = units_->timeUnit();
const SetupHold *tgt_min_max = setup_hold_->opposite();
VertexPathIterator src_iter(src_vertex, this);
while (src_iter.hasNext()) {
Path *src_path = src_iter.next();
const Clock *src_clk = src_path->clock(this);
if (src_path->isClock(this)
&& src_rf->matches(src_path->transition(this))
&& src_path->minMax(this) == setup_hold_
&& clk_set_.find(src_clk) != clk_set_.end()) {
Corner *src_corner = src_path->pathAnalysisPt(this)->corner();
if (corner_ == nullptr
|| src_corner == corner_) {
VertexPathIterator tgt_iter(tgt_vertex, this);
while (tgt_iter.hasNext()) {
Path *tgt_path = tgt_iter.next();
const Clock *tgt_clk = tgt_path->clock(this);
if (tgt_clk == src_clk
&& tgt_path->isClock(this)
&& tgt_rf->matches(tgt_path->transition(this))
&& tgt_path->minMax(this) == tgt_min_max
&& tgt_path->pathAnalysisPt(this)->corner() == src_corner) {
ClkSkew probe(src_path, tgt_path, include_internal_latency_, this);
ClkSkew &clk_skew = skews[src_clk];
debugPrint(debug_, "clk_skew", 2,
"%s %s %s -> %s %s %s crpr = %s skew = %s",
network_->pathName(src_path->pin(this)),
src_path->transition(this)->to_string().c_str(),
time_unit->asString(probe.srcLatency(this)),
network_->pathName(tgt_path->pin(this)),
tgt_path->transition(this)->to_string().c_str(),
time_unit->asString(probe.tgtLatency(this)),
delayAsString(probe.crpr(this), this),
time_unit->asString(probe.skew()));
if (clk_skew.srcPath() == nullptr
|| abs(probe.skew()) > abs(clk_skew.skew()))
clk_skew = probe;
}
}
}
}
}
}
VertexSet
ClkSkews::findFanout(Vertex *from)
{
VertexSet endpoints(graph_);
UnorderedSet<Vertex*> visited;
findFanout1(from, visited, endpoints);
return endpoints;
}
void
ClkSkews::findFanout1(Vertex *from,
UnorderedSet<Vertex*> &visited,
VertexSet &endpoints)
{
visited.insert(from);
if (from->hasChecks())
endpoints.insert(from);
if (fanout_pred_.searchFrom(from)) {
VertexOutEdgeIterator edge_iter(from, graph_);
while (edge_iter.hasNext()) {
Edge *edge = edge_iter.next();
Vertex *to = edge->to(graph_);
if (fanout_pred_.searchThru(edge)
&& fanout_pred_.searchTo(to)
// Do not revisit downstream fanout cones.
&& visited.insert(to).second)
findFanout1(to, visited, endpoints);
}
}
}
////////////////////////////////////////////////////////////////
FanOutSrchPred::FanOutSrchPred(const StaState *sta) :
SearchPred1(sta)
{
}
bool
FanOutSrchPred::searchThru(Edge *edge)
{
const TimingRole *role = edge->role();
return SearchPred1::searchThru(edge)
&& (role == TimingRole::wire()
|| role == TimingRole::combinational()
|| role == TimingRole::tristateEnable()
|| role == TimingRole::tristateDisable());
}
} // namespace
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