diff --git a/Changes b/Changes
index 861609fcf..91048143f 100644
--- a/Changes
+++ b/Changes
@@ -26,6 +26,8 @@ indicates the contributor was also the author of the fix; Thanks!
 
 ***  Add VARHIDDEN warning when signal name hides module name.
 
+***  Add experimental clock domain crossing checks.
+
 **** Support optional cell parenthesis, bug179. [by Byron Bradley]
 
 **** Support for loop i++, ++i, i--, --i, bug175. [by Byron Bradley]
diff --git a/bin/verilator b/bin/verilator
index e49b4bb19..a88cf99a3 100755
--- a/bin/verilator
+++ b/bin/verilator
@@ -193,6 +193,7 @@ descriptions in the next sections for more information.
     --bbox-unsup                Blackbox unsupported language features
     --bin <filename>            Override Verilator binary
     --cc                        Create C++ output
+    --cdc                       Clock domain crossing analysis
     --compiler <compiler-name>  Tune for specified C++ compiler
     --coverage                  Enable all coverage
     --coverage-line             Enable line coverage
@@ -254,6 +255,7 @@ descriptions in the next sections for more information.
     +define+<var>+<value>       Set preprocessor define
     +incdir+<dir>               Directory to search for includes
     +libext+<ext>+[ext]...      Extensions for finding modules
+    +notimingchecks             Ignored
 
 =head1 ARGUMENTS
 
@@ -308,6 +310,17 @@ output files.
 
 Specifies C++ without SystemC output mode; see also --sc and --sp.
 
+=item --cdc
+
+Experimental.  Perform some clock domain crossing checks and issue related
+warnings.  Additional warning information is written to the file
+{prefix}__cdc.txt.  Generally used with --lint-only.
+
+Currently only checks that asynchronous flop reset terms come from primary
+inputs (a check that most other CDC tools missed, so it was put here).  If
+you have interest in adding more traditional CDC checks, please contact the
+authors.
+
 =item --compiler I<compiler-name>
 
 Enables tunings and work-arounds for the specified C++ compiler.
@@ -992,6 +1005,7 @@ In certain optimization modes, it also creates:
     {prefix}__Syms.cpp			// Global symbol table C++
     {prefix}__Syms.h			// Global symbol table header
     {prefix}__Trace.cpp			// Wave file generation code (--trace)
+    {prefix}__cdc.txt			// Clock Domain Crossing checks (--cdc)
     {prefix}__stats.txt			// Statistics (--stats)
 
 It also creates internal files that can be mostly ignored:
diff --git a/src/Makefile_obj.in b/src/Makefile_obj.in
index f45dcdbc4..e667bf5e5 100644
--- a/src/Makefile_obj.in
+++ b/src/Makefile_obj.in
@@ -155,6 +155,7 @@ RAW_OBJS = \
 	V3Broken.o \
 	V3Case.o \
 	V3Cast.o \
+	V3Cdc.o \
 	V3Changed.o \
 	V3Clean.o \
 	V3ClkGater.o \
diff --git a/src/V3Cdc.cpp b/src/V3Cdc.cpp
new file mode 100644
index 000000000..d5ade9936
--- /dev/null
+++ b/src/V3Cdc.cpp
@@ -0,0 +1,629 @@
+//*************************************************************************
+// DESCRIPTION: Verilator: Clock Domain Crossing Lint
+//
+// Code available from: http://www.veripool.org/verilator
+//
+// AUTHORS: Wilson Snyder with Paul Wasson, Duane Gabli
+//
+//*************************************************************************
+//
+// Copyright 2003-2010 by Wilson Snyder.  This program is free software; you can
+// redistribute it and/or modify it under the terms of either the GNU
+// Lesser General Public License Version 3 or the Perl Artistic License
+// Version 2.0.
+//
+// Verilator 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.
+//
+//*************************************************************************
+// V3Cdc's Transformations:
+//
+// Create V3Graph-ish graph
+// Find all negedge reset flops
+// Trace back to previous flop
+//
+//*************************************************************************
+
+#include "config_build.h"
+#include "verilatedos.h"
+#include <cstdio>
+#include <cstdarg>
+#include <unistd.h>
+#include <algorithm>
+#include <iomanip>
+#include <vector>
+#include <deque>
+#include <list>
+#include <memory>
+
+#include "V3Global.h"
+#include "V3Cdc.h"
+#include "V3Ast.h"
+#include "V3Graph.h"
+#include "V3Const.h"
+#include "V3EmitV.h"
+#include "V3File.h"
+
+//######################################################################
+
+class CdcBaseVisitor : public AstNVisitor {
+public:
+    static int debug() {
+	static int level = -1;
+	if (VL_UNLIKELY(level < 0)) level = v3Global.opt.debugSrcLevel(__FILE__);
+	return level;
+    }
+};
+
+//######################################################################
+// Support classes
+
+class CdcEitherVertex : public V3GraphVertex {
+    AstScope*	m_scopep;
+    AstNode*	m_nodep;
+    AstSenTree*	m_srcDomainp;
+    bool	m_srcDomainSet;
+    AstSenTree*	m_dstDomainp;
+    bool	m_dstDomainSet;
+    bool	m_asyncPath;
+public:
+    CdcEitherVertex(V3Graph* graphp, AstScope* scopep, AstNode* nodep)
+	: V3GraphVertex(graphp), m_scopep(scopep), m_nodep(nodep)
+	, m_srcDomainp(NULL), m_srcDomainSet(false)
+	, m_dstDomainp(NULL), m_dstDomainSet(false)
+	, m_asyncPath(false) {}
+    virtual ~CdcEitherVertex() {}
+    // Accessors
+    AstScope* scopep() const { return m_scopep; }
+    AstNode* nodep() const { return m_nodep; }
+    AstSenTree* srcDomainp() const { return m_srcDomainp; }
+    void srcDomainp(AstSenTree* nodep) { m_srcDomainp = nodep; }
+    bool srcDomainSet() const { return m_srcDomainSet; }
+    void srcDomainSet(bool flag) { m_srcDomainSet = flag; }
+    AstSenTree* dstDomainp() const { return m_dstDomainp; }
+    void dstDomainp(AstSenTree* nodep) { m_dstDomainp = nodep; }
+    bool dstDomainSet() const { return m_dstDomainSet; }
+    void dstDomainSet(bool flag) { m_dstDomainSet = flag; }
+    bool asyncPath() const { return m_asyncPath; }
+    void asyncPath(bool flag) { m_asyncPath = flag; }
+};
+
+class CdcVarVertex : public CdcEitherVertex {
+    AstVarScope* m_varScp;
+    int		m_cntAsyncRst;
+    bool	m_fromFlop;
+public:
+    CdcVarVertex(V3Graph* graphp, AstScope* scopep, AstVarScope* varScp)
+	: CdcEitherVertex(graphp, scopep, varScp), m_varScp(varScp), m_cntAsyncRst(0), m_fromFlop(false) {}
+    virtual ~CdcVarVertex() {}
+    // Accessors
+    AstVarScope* varScp() const { return m_varScp; }
+    virtual string name() const { return (cvtToStr((void*)m_varScp)+" "+varScp()->name()); }
+    virtual string dotColor() const { return fromFlop() ? "green" : cntAsyncRst() ? "red" : "blue"; }
+    int cntAsyncRst() const { return m_cntAsyncRst; }
+    void cntAsyncRst(int flag) { m_cntAsyncRst=flag; }
+    bool fromFlop() const { return m_fromFlop; }
+    void fromFlop(bool flag) { m_fromFlop = flag; }
+};
+
+class CdcLogicVertex : public CdcEitherVertex {
+    bool	m_safe;
+public:
+    CdcLogicVertex(V3Graph* graphp, AstScope* scopep, AstNode* nodep, AstSenTree* sensenodep)
+	: CdcEitherVertex(graphp,scopep,nodep), m_safe(true) { srcDomainp(sensenodep); dstDomainp(sensenodep); }
+    virtual ~CdcLogicVertex() {}
+    // Accessors
+    virtual string name() const { return (cvtToStr((void*)nodep())+"@"+scopep()->prettyName()); }
+    virtual string dotColor() const { return safe() ? "black" : "yellow"; }
+    bool safe() const { return m_safe; }
+    void clearSafe(AstNode* nodep) { m_safe = false; nodep->user3(true); }
+};
+
+//######################################################################
+// Cdc class functions
+
+class CdcVisitor : public CdcBaseVisitor {
+private:
+    // NODE STATE
+    //Entire netlist:
+    // AstVarScope::user1p	-> CdcVarVertex* for usage var, 0=not set yet
+    // {statement}Node::user1p	-> CdcLogicVertex* for this statement
+    // AstNode::user3		-> bool  True indicates to print %% (via V3EmitV)
+    AstUser1InUse	m_inuser1;
+    AstUser3InUse	m_inuser3;
+
+    // STATE
+    V3Graph		m_graph;	// Scoreboard of var usages/dependencies
+    CdcLogicVertex*	m_logicVertexp;	// Current statement being tracked, NULL=ignored
+    AstScope*		m_scopep;	// Current scope being processed
+    AstNodeModule*	m_modp;		// Current module
+    AstSenTree*		m_domainp;	// Current sentree
+    bool		m_inDly;	// In delayed assign
+    int			m_senNumber;	// Number of senitems
+    string		m_ofFilename;	// Output filename
+    ofstream*		m_ofp;		// Output file
+
+    // METHODS
+    void iterateNewStmt(AstNode* nodep) {
+	if (m_scopep) {
+	    UINFO(4,"   STMT "<<nodep<<endl);
+	    m_logicVertexp = new CdcLogicVertex(&m_graph, m_scopep, nodep, m_domainp);
+	    if (m_domainp && m_domainp->hasClocked()) {  // To/from a flop
+		m_logicVertexp->srcDomainp(m_domainp);
+		m_logicVertexp->srcDomainSet(true);
+		m_logicVertexp->dstDomainp(m_domainp);
+		m_logicVertexp->dstDomainSet(true);
+	    }
+	    m_senNumber = 0;
+	    nodep->iterateChildren(*this);
+	    m_logicVertexp = NULL;
+
+	    if (0 && debug()>=9) {
+		UINFO(9, "Trace Logic:\n");
+		nodep->dumpTree(cout, "-log1: ");
+	    }
+	}
+    }
+
+    CdcVarVertex* makeVarVertex(AstVarScope* varscp) {
+	CdcVarVertex* vertexp = (CdcVarVertex*)(varscp->user1p());
+	if (!vertexp) {
+	    UINFO(6,"New vertex "<<varscp<<endl);
+	    vertexp = new CdcVarVertex(&m_graph, m_scopep, varscp);
+	    varscp->user1p(vertexp);
+	    if (varscp->varp()->isIO() && varscp->scopep()->isTop()) {}
+	    if (varscp->varp()->isUsedClock()) {}
+	}
+	if (m_senNumber > 1) vertexp->cntAsyncRst(vertexp->cntAsyncRst()+1);
+	return vertexp;
+    }
+
+    string pad(unsigned column, const string& in) {
+	string out = in;
+	while (out.length()<column) out += ' ';
+	return out;
+    }
+
+    void analyze();
+    void analyzeReset();
+
+    void edgeReport() {
+	// Make report of all signal names and what clock edges they have
+	UINFO(3,__FUNCTION__<<": "<<endl);
+
+	// Trace all sources and sinks
+	for (int traceDests=0; traceDests<2; ++traceDests) {
+	    UINFO(9, " Trace Direction "<<(traceDests?"dst":"src")<<endl);
+	    m_graph.userClearVertices();  // user1: bool - was analyzed
+	    for (V3GraphVertex* itp = m_graph.verticesBeginp(); itp; itp=itp->verticesNextp()) {
+		if (CdcVarVertex* vvertexp = dynamic_cast<CdcVarVertex*>(itp)) {
+		    UINFO(9, "   Trace One edge: "<<vvertexp<<endl);
+		    edgeDomainRecurse(vvertexp, traceDests, 0);
+		}
+	    }
+	}
+
+	string filename = v3Global.opt.makeDir()+"/"+v3Global.opt.prefix()+"__cdc_edges.txt";
+	const auto_ptr<ofstream> ofp (V3File::new_ofstream(filename));
+	if (ofp->fail()) v3fatalSrc("Can't write "<<filename);
+	*ofp<<"Edge Report for "<<v3Global.opt.prefix()<<endl;
+
+	deque<string> report;  // Sort output by name
+	for (V3GraphVertex* itp = m_graph.verticesBeginp(); itp; itp=itp->verticesNextp()) {
+	    if (CdcVarVertex* vvertexp = dynamic_cast<CdcVarVertex*>(itp)) {
+		AstVar* varp = vvertexp->varScp()->varp();
+		if (1) {  // varp->isPrimaryIO()
+		    const char* whatp = "wire";
+		    if (varp->isPrimaryIO()) whatp = (varp->isInout()?"inout":varp->isInput()?"input":"output");
+
+		    ostringstream os;
+		    os.setf(ios::left);
+		    os<<"  "<<setw(8)<<whatp;
+		    os<<"  "<<setw(40)<<vvertexp->varScp()->prettyName();
+		    os<<"  SRC=";
+		    if (vvertexp->srcDomainp()) V3EmitV::verilogForTree(vvertexp->srcDomainp(), os);
+		    os<<"  DST=";
+		    if (vvertexp->dstDomainp()) V3EmitV::verilogForTree(vvertexp->dstDomainp(), os);
+		    os<<"\n";
+		    report.push_back(os.str());
+		}
+	    }
+	}
+	sort(report.begin(), report.end());
+	for (deque<string>::iterator it = report.begin(); it!=report.end(); ++it) {
+	    *ofp << *it;
+	}
+    }
+
+    string spaces(int level) { string out; while (level--) out+=" "; return out; }
+
+    void edgeDomainRecurse(CdcEitherVertex* vertexp, bool traceDests, int level) {
+	// Scan back to inputs/outputs, flops, and compute clock domain information
+	UINFO(8,spaces(level)<<"     Tracein  "<<vertexp<<endl);
+	if (vertexp->user()) return;   // Mid-Processed - prevent loop
+	vertexp->user(true);
+	// Variables from flops already are domained
+	if (traceDests ? vertexp->dstDomainSet() : vertexp->srcDomainSet()) return;  // Fully computed
+
+	typedef set<AstSenTree*> SenSet;
+	SenSet 	    senouts;   // List of all sensitivities for new signal
+	if (CdcLogicVertex* vvertexp = dynamic_cast<CdcLogicVertex*>(vertexp)) {
+	    if (vvertexp) {}  // Unused
+	}
+	else if (CdcVarVertex* vvertexp = dynamic_cast<CdcVarVertex*>(vertexp)) {
+	    // If primary I/O, give it domain of the input
+	    AstVar* varp = vvertexp->varScp()->varp();
+	    if (varp->isPrimaryIO() && varp->isInput() && !traceDests) {
+		senouts.insert(new AstSenTree(varp->fileline(), new AstSenItem(varp->fileline(), AstSenItem::Combo())));
+	    }
+	}
+
+	// Now combine domains of sources/dests
+	if (traceDests) {
+	    for (V3GraphEdge* edgep = vertexp->outBeginp(); edgep; edgep = edgep->outNextp()) {
+		CdcEitherVertex* eToVertexp = (CdcEitherVertex*)edgep->top();
+		edgeDomainRecurse(eToVertexp, traceDests, level+1);
+		if (eToVertexp->dstDomainp()) senouts.insert(eToVertexp->dstDomainp());
+	    }
+	} else {
+	    for (V3GraphEdge* edgep = vertexp->inBeginp(); edgep; edgep = edgep->inNextp()) {
+		CdcEitherVertex* eFromVertexp = (CdcEitherVertex*)edgep->fromp();
+		edgeDomainRecurse(eFromVertexp, traceDests, level+1);
+		if (eFromVertexp->srcDomainp()) senouts.insert(eFromVertexp->srcDomainp());
+	    }
+	}
+
+	// Convert list of senses into one sense node
+	AstSenTree* senoutp = NULL;
+	bool	    senedited = false;
+	for (SenSet::iterator it=senouts.begin(); it!=senouts.end(); ++it) {
+	    if (!senoutp) senoutp = *it;
+	    else {
+		if (!senedited) {
+		    senedited = true;
+		    senoutp = senoutp->cloneTree(true);
+		}
+		senoutp->addSensesp((*it)->sensesp()->cloneTree(true));
+	    }
+	}
+	// If multiple domains need to do complicated optimizations
+	if (senedited) {
+	    senoutp = V3Const::constifyExpensiveEdit(senoutp)->castSenTree();
+	}
+	if (traceDests) {
+	    vertexp->dstDomainSet(true);  // Note it's set - domainp may be null, so can't use that
+	    vertexp->dstDomainp(senoutp);
+	    if (debug()>=9) {
+		UINFO(9,spaces(level)+"     Tracedst "<<vertexp);
+		if (senoutp) V3EmitV::verilogForTree(senoutp, cout); cout<<endl;
+	    }
+	} else {
+	    vertexp->srcDomainSet(true);  // Note it's set - domainp may be null, so can't use that
+	    vertexp->srcDomainp(senoutp);
+	    if (debug()>=9) {
+		UINFO(9,spaces(level)+"     Tracesrc "<<vertexp);
+		if (senoutp) V3EmitV::verilogForTree(senoutp, cout); cout<<endl;
+	    }
+	}
+    }
+
+    CdcEitherVertex* traceAsyncRecurse(CdcEitherVertex* vertexp, uint32_t did_value, bool mark);
+    void dumpAsync(CdcVarVertex* vertexp, CdcEitherVertex* markp);
+    void dumpAsyncRecurse(CdcEitherVertex* vertexp, const string& prefix, const string& blank);
+
+    void warnAndFile(AstNode* nodep, V3ErrorCode code, const string& msg) {
+	static bool told_file = false;
+	nodep->v3warnCode(code,msg);
+	if (!told_file) {
+	    told_file = 1;
+	    cerr<<V3Error::msgPrefix()<<"     See details in "<<m_ofFilename<<endl;
+	}
+	*m_ofp<<"%Warning-"<<code.ascii()<<": "<<nodep->fileline()<<" "<<msg<<endl;
+    }
+
+    void clearNodeSafe(AstNode* nodep) {
+	// Need to not clear if warnings are off (rather than when report it)
+	// as bypassing this warning may turn up another path that isn't warning off'ed.
+	if (m_logicVertexp && !nodep->fileline()->warnIsOff(V3ErrorCode::CDCRSTLOGIC)) {
+	    UINFO(9,"Clear safe "<<nodep<<endl);
+	    m_logicVertexp->clearSafe(nodep);
+	}
+    }
+
+    // VISITORS
+    virtual void visit(AstNodeModule* nodep, AstNUser*) {
+	m_modp = nodep;
+	nodep->iterateChildren(*this);
+	m_modp = NULL;
+    }
+    virtual void visit(AstScope* nodep, AstNUser*) {
+	UINFO(4," SCOPE "<<nodep<<endl);
+	m_scopep = nodep;
+	m_logicVertexp = NULL;
+	nodep->iterateChildren(*this);
+	m_scopep = NULL;
+    }
+    virtual void visit(AstActive* nodep, AstNUser*) {
+	// Create required blocks and add to module
+	UINFO(4,"  BLOCK  "<<nodep<<endl);
+	m_domainp = nodep->sensesp();
+	if (!m_domainp || m_domainp->hasCombo() || m_domainp->hasClocked()) {  // IE not hasSettle/hasInitial
+	    iterateNewStmt(nodep);
+	}
+	m_domainp = NULL;
+    }
+    virtual void visit(AstNodeVarRef* nodep, AstNUser*) {
+	if (m_scopep) {
+	    if (!m_logicVertexp) nodep->v3fatalSrc("Var ref not under a logic block\n");
+	    AstVarScope* varscp = nodep->varScopep();
+	    if (!varscp) nodep->v3fatalSrc("Var didn't get varscoped in V3Scope.cpp\n");
+	    CdcVarVertex* varvertexp = makeVarVertex(varscp);
+	    UINFO(5," VARREF to "<<varscp<<endl);
+	    // We use weight of one; if we ref the var more than once, when we simplify,
+	    // the weight will increase
+	    if (nodep->lvalue()) {
+		new V3GraphEdge(&m_graph, m_logicVertexp, varvertexp, 1);
+		if (m_inDly) {
+		    varvertexp->fromFlop(true);
+		    varvertexp->srcDomainp(m_domainp);
+		    varvertexp->srcDomainSet(true);
+		}
+	    } else {
+		new V3GraphEdge(&m_graph, varvertexp, m_logicVertexp, 1);
+	    }
+	}
+    }
+    virtual void visit(AstAssignDly* nodep, AstNUser*) {
+	m_inDly = true;
+	nodep->iterateChildren(*this);
+	m_inDly = false;
+    }
+    virtual void visit(AstSenItem* nodep, AstNUser*) {
+	// Note we look at only AstSenItems, not AstSenGate's
+	// The gating term of a AstSenGate is normal logic
+	m_senNumber++;
+	nodep->iterateChildren(*this);
+    }
+    virtual void visit(AstAlways* nodep, AstNUser*) {
+	iterateNewStmt(nodep);
+    }
+    virtual void visit(AstCFunc* nodep, AstNUser*) {
+	iterateNewStmt(nodep);
+    }
+    virtual void visit(AstSenGate* nodep, AstNUser*) {
+	// First handle the clock part will be handled in a minute by visit AstSenItem
+	// The logic gating term is delt with as logic
+	iterateNewStmt(nodep);
+    }
+    virtual void visit(AstAssignAlias* nodep, AstNUser*) {
+	iterateNewStmt(nodep);
+    }
+    virtual void visit(AstAssignW* nodep, AstNUser*) {
+	iterateNewStmt(nodep);
+    }
+
+    // Math that shouldn't cause us to clear safe
+    virtual void visit(AstConst* nodep, AstNUser*) { }
+    virtual void visit(AstReplicate* nodep, AstNUser*) {
+	nodep->iterateChildren(*this);
+    }
+    virtual void visit(AstConcat* nodep, AstNUser*) {
+	nodep->iterateChildren(*this);
+    }
+    virtual void visit(AstNot* nodep, AstNUser*) {
+	nodep->iterateChildren(*this);
+    }
+    virtual void visit(AstSel* nodep, AstNUser*) {
+	if (!nodep->lsbp()->castConst()) clearNodeSafe(nodep);
+	nodep->iterateChildren(*this);
+    }
+    virtual void visit(AstNodeSel* nodep, AstNUser*) {
+	if (!nodep->bitp()->castConst()) clearNodeSafe(nodep);
+	nodep->iterateChildren(*this);
+    }
+
+    // Ignores
+    virtual void visit(AstInitial* nodep, AstNUser*) { }
+    virtual void visit(AstTraceInc* nodep, AstNUser*) { }
+    virtual void visit(AstCoverToggle* nodep, AstNUser*) { }
+
+    //--------------------
+    // Default
+    virtual void visit(AstNodeMath* nodep, AstNUser*) {
+	clearNodeSafe(nodep);
+	nodep->iterateChildren(*this);
+    }
+    virtual void visit(AstNode* nodep, AstNUser*) {
+	nodep->iterateChildren(*this);
+    }
+
+public:
+    // CONSTUCTORS
+    CdcVisitor(AstNode* nodep) {
+	m_logicVertexp = NULL;
+	m_scopep = NULL;
+	m_modp = NULL;
+	m_domainp = NULL;
+	m_inDly = false;
+	m_senNumber = 0;
+
+	// Make report of all signal names and what clock edges they have
+	string filename = v3Global.opt.makeDir()+"/"+v3Global.opt.prefix()+"__cdc.txt";
+	m_ofp = V3File::new_ofstream(filename);
+	if (m_ofp->fail()) v3fatalSrc("Can't write "<<filename);
+	m_ofFilename = filename;
+	*m_ofp<<"CDC Report for "<<v3Global.opt.prefix()<<endl;
+	*m_ofp<<"Each dump below traces a variable from a flop back through logic.\n";
+	*m_ofp<<"First the variable is listed, then the logic that creates it, then all variables\n";
+	*m_ofp<<"feeding that logic, recursively backwards to the sourcing flop(s).\n";
+	*m_ofp<<"%% Indicates nodes considered potentially unsafe.\n";
+
+	nodep->accept(*this);
+	analyze();
+	//edgeReport();  // Not useful at the moment
+
+	if (0) { *m_ofp<<"\nDBG-test-dumper\n"; V3EmitV::verilogPrefixedTree(nodep, *m_ofp, "DBG ",true); *m_ofp<<endl; }
+    }
+    virtual ~CdcVisitor() {
+	if (m_ofp) { delete m_ofp; m_ofp = NULL; }
+    }
+};
+
+//######################################################################
+// Cdc class functions
+
+class CdcDumpVisitor : public CdcBaseVisitor {
+private:
+    // NODE STATE
+    //Entire netlist:
+    // {statement}Node::user3p	-> bool, indicating not safe
+    ofstream*		m_ofp;		// Output file
+    string		m_prefix;
+
+    virtual void visit(AstNode* nodep, AstNUser*) {
+	*m_ofp<<m_prefix;
+	if (nodep->user3()) *m_ofp<<" %%";
+	else *m_ofp<<"  ";
+	*m_ofp<<nodep->prettyTypeName()<<" "<<endl;
+	string lastPrefix = m_prefix;
+	m_prefix = lastPrefix + "1:";
+	nodep->op1p()->iterateAndNext(*this);
+	m_prefix = lastPrefix + "2:";
+	nodep->op2p()->iterateAndNext(*this);
+	m_prefix = lastPrefix + "3:";
+	nodep->op3p()->iterateAndNext(*this);
+	m_prefix = lastPrefix + "4:";
+	nodep->op4p()->iterateAndNext(*this);
+	m_prefix = lastPrefix;
+    }
+
+public:
+    // CONSTUCTORS
+    CdcDumpVisitor(AstNode* nodep, ofstream* ofp, const string& prefix) {
+	m_ofp = ofp;
+	m_prefix = prefix;
+	nodep->accept(*this);
+    }
+    virtual ~CdcDumpVisitor() {}
+};
+
+//######################################################################
+
+void CdcVisitor::analyze() {
+    UINFO(3,__FUNCTION__<<": "<<endl);
+    //if (debug()>6) m_graph.dump();
+    if (debug()>6) m_graph.dumpDotFilePrefixed("cdc_pre");
+    m_graph.removeRedundantEdgesSum(&V3GraphEdge::followAlwaysTrue);
+    m_graph.dumpDotFilePrefixed("cdc_simp");
+    //
+    analyzeReset();
+}
+
+void CdcVisitor::analyzeReset() {
+    // Find all async reset wires, and trace backwards
+    for (V3GraphVertex* itp = m_graph.verticesBeginp(); itp; itp=itp->verticesNextp()) {
+	if (CdcVarVertex* vvertexp = dynamic_cast<CdcVarVertex*>(itp)) {
+	    if (vvertexp->cntAsyncRst()) {
+		m_graph.userClearVertices();  // user1: bool - was analyzed
+		UINFO(9, "   Trace One async: "<<vvertexp<<endl);
+		// Twice, as we need to detect, then propagate
+		CdcEitherVertex* markp = traceAsyncRecurse(vvertexp, 1, false);
+		if (markp) { // Mark is non-NULL if something bad on this path
+		    UINFO(9, "   Trace One bad! "<<vvertexp<<endl);
+		    traceAsyncRecurse(vvertexp, 2, true);
+		    m_graph.userClearVertices();  // user1: bool - was analyzed
+		    dumpAsync(vvertexp, markp);
+		}
+	    }
+	}
+    }
+}
+
+CdcEitherVertex* CdcVisitor::traceAsyncRecurse(CdcEitherVertex* vertexp, uint32_t did_value, bool mark) {
+    // Return vertex of any dangerous stuff attached, or NULL if OK
+    // If mark, also mark the output even if nothing dangerous below
+    CdcEitherVertex* mark_outp = NULL;
+    UINFO(9,"      Trace: "<<vertexp<<endl);
+
+    if (vertexp->user()>=did_value) return false;   // Processed - prevent loop
+    vertexp->user(did_value);
+
+    if (CdcLogicVertex* vvertexp = dynamic_cast<CdcLogicVertex*>(vertexp)) {
+	// Any logic considered bad, at the moment, anyhow
+	if (!vvertexp->safe() && !mark_outp) mark_outp = vvertexp;
+	// And keep tracing back so the user can understand what's up
+    }
+    else if (CdcVarVertex* vvertexp = dynamic_cast<CdcVarVertex*>(vertexp)) {
+	if (mark) vvertexp->asyncPath(true);
+	// If primary I/O, it's ok here back
+	if (vvertexp->varScp()->varp()->isInput()) return false;
+	// Also ok if from flop
+	if (vvertexp->fromFlop()) return false;
+    }
+
+    for (V3GraphEdge* edgep = vertexp->inBeginp(); edgep; edgep = edgep->inNextp()) {
+	CdcEitherVertex* eFromVertexp = (CdcEitherVertex*)edgep->fromp();
+	CdcEitherVertex* submarkp = traceAsyncRecurse(eFromVertexp, did_value, mark);
+	if (submarkp && !mark_outp) mark_outp = submarkp;
+    }
+
+    if (mark) vertexp->asyncPath(true);
+    return mark_outp;
+}
+
+//----------------------------------------------------------------------
+
+void CdcVisitor::dumpAsync(CdcVarVertex* vertexp, CdcEitherVertex* markp) {
+    AstNode* nodep = vertexp->varScp();
+    *m_ofp<<"\n";
+    *m_ofp<<"\n";
+    AstNode* targetp = vertexp->nodep();
+    if (V3GraphEdge* edgep = vertexp->outBeginp()) {
+	CdcEitherVertex* eToVertexp = (CdcEitherVertex*)edgep->top();
+	targetp = eToVertexp->nodep();
+    }
+    warnAndFile(markp->nodep(),V3ErrorCode::CDCRSTLOGIC,"Logic in path that feeds async reset, via signal: "+nodep->prettyName());
+    *m_ofp<<"Fanout: "<<vertexp->cntAsyncRst()<<"  Target: "<<targetp->fileline()<<endl;
+    dumpAsyncRecurse(vertexp," +--", " |  ");
+}
+
+void CdcVisitor::dumpAsyncRecurse(CdcEitherVertex* vertexp, const string& prefix, const string& blank) {
+    // Return true if any dangerous stuff attached
+    // If mark, also mark the output even if nothing dangerous below
+    if (vertexp->user()) return;   // Processed - prevent loop
+    vertexp->user(1);
+    if (!vertexp->asyncPath()) return;  // Not part of path
+
+    *m_ofp<<V3OutFile::indentSpaces(40)<<" "<<blank<<"\n";
+
+    // Dump single variable/logic block
+    // See also OrderGraph::loopsVertexCb(V3GraphVertex* vertexp)
+    {
+	AstNode* nodep = vertexp->nodep();
+	string front = pad(40,nodep->fileline()->ascii()+":");
+	front += " "+prefix+" ";
+	if (nodep->castVarScope()) *m_ofp<<front<<"Variable: "<<nodep->prettyName()<<endl;
+	else {
+	    V3EmitV::verilogPrefixedTree(nodep, *m_ofp, prefix+" ", true);
+	    if (debug()) {
+		CdcDumpVisitor visitor (nodep, m_ofp, front+"DBG: ");
+	    }
+	}
+    }
+
+    // Now do the other logic in the path
+    for (V3GraphEdge* edgep = vertexp->inBeginp(); edgep; edgep = edgep->inNextp()) {
+	CdcEitherVertex* eFromVertexp = (CdcEitherVertex*)edgep->fromp();
+	dumpAsyncRecurse(eFromVertexp, blank+" +--", blank+" |  ");
+    }
+}
+
+//######################################################################
+// Cdc class functions
+
+void V3Cdc::cdcAll(AstNetlist* nodep) {
+    UINFO(2,__FUNCTION__<<": "<<endl);
+    CdcVisitor visitor (nodep);
+}
diff --git a/src/V3Cdc.h b/src/V3Cdc.h
new file mode 100644
index 000000000..f20215eb0
--- /dev/null
+++ b/src/V3Cdc.h
@@ -0,0 +1,37 @@
+// -*- C++ -*-
+//*************************************************************************
+// DESCRIPTION: Verilator: Break always into sensitivity block domains
+//
+// Code available from: http://www.veripool.org/verilator
+//
+// AUTHORS: Wilson Snyder with Paul Wasson, Duane Gabli
+//
+//*************************************************************************
+//
+// Copyright 2003-2010 by Wilson Snyder.  This program is free software; you can
+// redistribute it and/or modify it under the terms of either the GNU
+// Lesser General Public License Version 3 or the Perl Artistic License
+// Version 2.0.
+//
+// Verilator 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.
+//
+//*************************************************************************
+
+#ifndef _V3CDC_H_
+#define _V3CDC_H_ 1
+#include "config_build.h"
+#include "verilatedos.h"
+#include "V3Error.h"
+#include "V3Ast.h"
+
+//============================================================================
+
+class V3Cdc {
+public:
+    static void cdcAll(AstNetlist* nodep);
+};
+
+#endif // Guard
diff --git a/src/V3EmitV.cpp b/src/V3EmitV.cpp
index 025fa9e5d..c99d4f3eb 100644
--- a/src/V3EmitV.cpp
+++ b/src/V3EmitV.cpp
@@ -50,7 +50,8 @@ class EmitVBaseVisitor : public EmitCBaseVisitor {
 
     virtual void puts(const string& str) = 0;
     virtual void putbs(const string& str) = 0;
-    virtual void putfs(AstNode* nodep, const string& str) = 0;
+    virtual void putfs(AstNode* nodep, const string& str) = 0;  // Fileline and node %% mark
+    virtual void putqs(AstNode* nodep, const string& str) = 0;  // Fileline quiet w/o %% mark
     virtual void putsNoTracking(const string& str) = 0;
     virtual void putsQuoted(const string& str) {
 	// Quote \ and " for use inside C programs
@@ -68,16 +69,16 @@ class EmitVBaseVisitor : public EmitCBaseVisitor {
     virtual void visit(AstModule* nodep, AstNUser*) {
 	putfs(nodep, "module "+modClassName(nodep)+";\n");
 	nodep->iterateChildren(*this);
-	putfs(nodep, "endmodule\n");
+	putqs(nodep, "endmodule\n");
     }
     virtual void visit(AstNodeFTask* nodep, AstNUser*) {
 	putfs(nodep, nodep->isFunction() ? "function":"task");
 	puts(" ");
 	puts(nodep->name());
 	puts(";\n");
-	putfs(nodep, "begin\n");
+	putqs(nodep, "begin\n");  // Only putfs the first time for each visitor; later for same node is putqs
 	nodep->stmtsp()->iterateAndNext(*this);
-	putfs(nodep, "end\n");
+	putqs(nodep, "end\n");
     }
 
     virtual void visit(AstBegin* nodep, AstNUser*) {
@@ -88,17 +89,17 @@ class EmitVBaseVisitor : public EmitCBaseVisitor {
     virtual void visit(AstGenerate* nodep, AstNUser*) {
 	putfs(nodep, "generate\n");
 	nodep->iterateChildren(*this);
-	putfs(nodep, "end\n");
+	putqs(nodep, "end\n");
     }
     virtual void visit(AstFinal* nodep, AstNUser*) {
 	putfs(nodep, "final begin\n");
 	nodep->iterateChildren(*this);
-	putfs(nodep, "end\n");
+	putqs(nodep, "end\n");
     }
     virtual void visit(AstInitial* nodep, AstNUser*) {
 	putfs(nodep,"initial begin\n");
 	nodep->iterateChildren(*this);
-	putfs(nodep, "end\n");
+	putqs(nodep, "end\n");
     }
     virtual void visit(AstAlways* nodep, AstNUser*) {
 	putfs(nodep,"always ");
@@ -106,7 +107,7 @@ class EmitVBaseVisitor : public EmitCBaseVisitor {
 	else nodep->sensesp()->iterateAndNext(*this);
 	putbs(" begin\n");
 	nodep->bodysp()->iterateAndNext(*this);
-	putfs(nodep,"end\n");
+	putqs(nodep,"end\n");
     }
     virtual void visit(AstNodeAssign* nodep, AstNUser*) {
 	nodep->lhsp()->iterateAndNext(*this);
@@ -139,7 +140,7 @@ class EmitVBaseVisitor : public EmitCBaseVisitor {
 	putfs(nodep,"@(");
 	for (AstNode* expp=nodep->sensesp(); expp; expp = expp->nextp()) {
 	    expp->accept(*this);
-	    if (expp->nextp()) putfs(expp->nextp()," or ");
+	    if (expp->nextp()) putqs(expp->nextp()," or ");
 	}
 	puts(")");
     }
@@ -165,7 +166,7 @@ class EmitVBaseVisitor : public EmitCBaseVisitor {
 	    }
 	}
 	nodep->itemsp()->iterateAndNext(*this);
-	putfs(nodep,"endcase\n");
+	putqs(nodep,"endcase\n");
     }
     virtual void visit(AstCaseItem* nodep, AstNUser*) {
 	if (nodep->condsp()) {
@@ -173,7 +174,7 @@ class EmitVBaseVisitor : public EmitCBaseVisitor {
 	} else putbs("default");
 	putfs(nodep,": begin ");
 	nodep->bodysp()->iterateAndNext(*this);
-	putfs(nodep,"end\n");
+	putqs(nodep,"end\n");
     }
     virtual void visit(AstComment* nodep, AstNUser*) {
 	puts((string)"// "+nodep->name()+"\n");
@@ -253,7 +254,7 @@ class EmitVBaseVisitor : public EmitCBaseVisitor {
 	m_suppressSemi = false;
 	puts(") begin\n");
 	nodep->bodysp()->iterateAndNext(*this);
-	putfs(nodep,"end\n");
+	putqs(nodep,"end\n");
     }
     virtual void visit(AstRepeat* nodep, AstNUser*) {
 	putfs(nodep,"repeat (");
@@ -277,11 +278,11 @@ class EmitVBaseVisitor : public EmitCBaseVisitor {
 	puts(") begin\n");
 	nodep->ifsp()->iterateAndNext(*this);
 	if (nodep->elsesp()) {
-	    putfs(nodep,"end\n");
-	    putfs(nodep,"else begin\n");
+	    putqs(nodep,"end\n");
+	    putqs(nodep,"else begin\n");
 	    nodep->elsesp()->iterateAndNext(*this);
 	}
-	putfs(nodep,"end\n");
+	putqs(nodep,"end\n");
     }
     virtual void visit(AstStop* nodep, AstNUser*) {
 	putfs(nodep,"$stop;\n");
@@ -437,12 +438,12 @@ class EmitVBaseVisitor : public EmitCBaseVisitor {
     // Terminals
     virtual void visit(AstVarRef* nodep, AstNUser*) {
 	putfs(nodep,nodep->hiername());
-	puts(nodep->varp()->name());
+	puts(nodep->varp()->prettyName());
     }
     virtual void visit(AstVarXRef* nodep, AstNUser*) {
 	putfs(nodep,nodep->dotted());
 	puts(".");
-	puts(nodep->varp()->name());
+	puts(nodep->varp()->prettyName());
     }
     virtual void visit(AstConst* nodep, AstNUser*) {
 	putfs(nodep,nodep->num().ascii(true,true));
@@ -458,13 +459,13 @@ class EmitVBaseVisitor : public EmitCBaseVisitor {
     virtual void visit(AstVar* nodep, AstNUser*) {
 	putfs(nodep,nodep->verilogKwd());
 	puts(" ");
-	nodep->dtypep()->iterateChildren(*this); puts(" ");
+	nodep->dtypep()->iterateAndNext(*this); puts(" ");
 	puts(nodep->name());
 	puts(";\n");
     }
     virtual void visit(AstActive* nodep, AstNUser*) {
 	m_sensesp = nodep->sensesp();
-	nodep->iterateChildren(*this);
+	nodep->stmtsp()->iterateAndNext(*this);
 	m_sensesp = NULL;
     }
     virtual void visit(AstVarScope*, AstNUser*) {}
@@ -501,8 +502,8 @@ class EmitVFileVisitor : public EmitVBaseVisitor {
     virtual void puts(const string& str) { ofp()->puts(str); }
     virtual void putbs(const string& str) { ofp()->putbs(str); }
     virtual void putfs(AstNode*, const string& str) { putbs(str); }
+    virtual void putqs(AstNode*, const string& str) { putbs(str); }
     virtual void putsNoTracking(const string& str) { ofp()->putsNoTracking(str); }
-    
 public:
     EmitVFileVisitor(AstNode* nodep, V3OutFile* ofp) {
 	m_ofp = ofp;
@@ -518,12 +519,12 @@ class EmitVStreamVisitor : public EmitVBaseVisitor {
     // MEMBERS
     ostream&	m_os;
     // METHODS
-    virtual void puts(const string& str) { m_os<<str; }
-    virtual void putbs(const string& str) { m_os<<str; }
-    virtual void putfs(AstNode*, const string& str) { putbs(str); }
     virtual void putsNoTracking(const string& str) { m_os<<str; }
-    
-public:
+    virtual void puts(const string& str) { putsNoTracking(str); }
+    virtual void putbs(const string& str) { puts(str); }
+    virtual void putfs(AstNode*, const string& str) { putbs(str); }
+    virtual void putqs(AstNode*, const string& str) { putbs(str); }
+ public:
     EmitVStreamVisitor(AstNode* nodep, ostream& os)
 	: m_os(os) {
 	nodep->accept(*this);
@@ -531,6 +532,75 @@ public:
     virtual ~EmitVStreamVisitor() {}
 };
 
+//######################################################################
+// Emit to a stream (perhaps stringstream)
+
+class EmitVPrefixedFormatter : public V3OutFormatter {
+    ostream&	m_os;
+    string	m_prefix;	// What to print at beginning of each line
+    int		m_column;	// Rough location; need just zero or non-zero
+    FileLine*	m_prefixFl;
+    // METHODS
+    virtual void putcOutput(char chr) {
+	if (chr == '\n') {
+	    m_column = 0;
+	    m_os<<chr;
+	} else {
+	    if (m_column == 0) {
+		m_column = 10;
+		m_os<<m_prefixFl->ascii()+":";
+		m_os<<V3OutFile::indentSpaces(40-(m_prefixFl->ascii().length()+1));
+		m_os<<" ";
+		m_os<<m_prefix;
+	    }
+	    m_column++;
+	    m_os<<chr;
+	}
+    }
+public:
+    void prefixFl(FileLine* fl) { m_prefixFl = fl; }
+    FileLine* prefixFl() const { return m_prefixFl; }
+    int column() const { return m_column; }
+    EmitVPrefixedFormatter(ostream& os, const string& prefix)
+	: V3OutFormatter("__STREAM", true), m_os(os), m_prefix(prefix) {
+	m_column = 0;
+	m_prefixFl = v3Global.rootp()->fileline();  // NETLIST's fileline instead of NULL to avoid NULL checks
+    }
+    virtual ~EmitVPrefixedFormatter() {
+	if (m_column) puts("\n");
+    }
+};
+
+class EmitVPrefixedVisitor : public EmitVBaseVisitor {
+    // MEMBERS
+    EmitVPrefixedFormatter m_formatter; // Special verilog formatter (Way down the inheritance is another unused V3OutFormatter)
+    bool	m_user3mark;	// nodep->user3() if set means mark with %%
+    // METHODS
+    virtual void putsNoTracking(const string& str) { m_formatter.putsNoTracking(str); }
+    virtual void puts(const string& str) { m_formatter.puts(str); }
+    // We don't use m_formatter's putbs because the tokens will change filelines
+    // and insert returns at the proper locations
+    virtual void putbs(const string& str) { m_formatter.puts(str); }
+    virtual void putfs(AstNode* nodep, const string& str) { putfsqs(nodep,str,false); }
+    virtual void putqs(AstNode* nodep, const string& str) { putfsqs(nodep,str,true); }
+    void putfsqs(AstNode* nodep, const string& str, bool quiet) {
+	if (m_formatter.prefixFl() != nodep->fileline()) {
+	    m_formatter.prefixFl(nodep->fileline());
+	    if (m_formatter.column()) puts("\n");  // This in turn will print the m_prefixFl
+	}
+	if (!quiet && nodep->user3()) puts("%%");
+	putbs(str);
+    }
+
+public:
+    EmitVPrefixedVisitor(AstNode* nodep, ostream& os, const string& prefix, bool user3mark)
+	: m_formatter(os, prefix), m_user3mark(user3mark) {
+	if (user3mark) { AstUser3InUse::check(); }
+	nodep->accept(*this);
+    }
+    virtual ~EmitVPrefixedVisitor() {}
+};
+
 //######################################################################
 // EmitV class functions
 
@@ -556,3 +626,7 @@ void V3EmitV::emitv() {
 void V3EmitV::verilogForTree(AstNode* nodep, ostream& os) {
     EmitVStreamVisitor(nodep, os);
 }
+
+void V3EmitV::verilogPrefixedTree(AstNode* nodep, ostream& os, const string& prefix, bool user3mark) {
+    EmitVPrefixedVisitor(nodep, os, prefix, user3mark);
+}
diff --git a/src/V3EmitV.h b/src/V3EmitV.h
index 89447593b..47056839d 100644
--- a/src/V3EmitV.h
+++ b/src/V3EmitV.h
@@ -33,6 +33,7 @@ class V3EmitV {
 public:
     static void emitv();
     static void verilogForTree(AstNode* nodep, ostream& os=cout);
+    static void verilogPrefixedTree(AstNode* nodep, ostream& os, const string& prefix, bool user3percent);
 };
 
 #endif // Guard
diff --git a/src/V3Error.h b/src/V3Error.h
index 5a84104fa..ab0f150f0 100644
--- a/src/V3Error.h
+++ b/src/V3Error.h
@@ -56,6 +56,7 @@ public:
 	CASEOVERLAP,	// Case statements overlap
 	CASEWITHX,	// Case with X values
 	CASEX,		// Casex
+	CDCRSTLOGIC,	// Logic in async reset path
 	CMPCONST,	// Comparison is constant due to limited range
 	COMBDLY,	// Combinatorial delayed assignment
 	STMTDLY,	// Delayed statement
@@ -95,7 +96,7 @@ public:
 	    // Warnings
 	    " FIRST_WARN",
 	    "BLKANDNBLK",
-	    "CASEINCOMPLETE", "CASEOVERLAP", "CASEWITHX", "CASEX", "CMPCONST",
+	    "CASEINCOMPLETE", "CASEOVERLAP", "CASEWITHX", "CASEX", "CDCRSTLOGIC", "CMPCONST",
 	    "COMBDLY", "STMTDLY", "SYMRSVDWORD", "GENCLK", "IMPERFECTSCH", "IMPLICIT", "IMPURE",
 	    "LITENDIAN",
 	    "MULTIDRIVEN", "REDEFMACRO",
@@ -185,7 +186,8 @@ inline void v3errorEnd(ostringstream& sstr) { V3Error::v3errorEnd(sstr); }
 
 // These allow errors using << operators: v3error("foo"<<"bar");
 // Careful, you can't put () around msg, as you would in most macro definitions
-#define v3warn(code,msg) v3errorEnd(((V3Error::v3errorPrep(V3ErrorCode::code)<<msg),V3Error::v3errorStr()));
+#define v3warnCode(code,msg) v3errorEnd(((V3Error::v3errorPrep(code)<<msg),V3Error::v3errorStr()));
+#define v3warn(code,msg) v3warnCode(V3ErrorCode::code,msg)
 #define v3info(msg)  v3warn(INFO,msg)
 #define v3fatal(msg) v3warn(FATAL,msg)
 #define v3error(msg) v3warn(ERROR,msg)
diff --git a/src/V3File.cpp b/src/V3File.cpp
index 4576b8cd6..657e52fd5 100644
--- a/src/V3File.cpp
+++ b/src/V3File.cpp
@@ -269,9 +269,11 @@ const char* V3OutFormatter::indentStr(int num) {
     static char str[MAXSPACE+20];
     char* cp = str;
     if (num>MAXSPACE) num=MAXSPACE;
-    while (num>=8) {
-	*cp++ = '\t';
-	num -= 8;
+    if (!m_verilog) {  // verilogPrefixedTree doesn't want tabs
+	while (num>=8) {
+	    *cp++ = '\t';
+	    num -= 8;
+	}
     }
     while (num>0) {
 	*cp++ = ' ';
diff --git a/src/V3File.h b/src/V3File.h
index 01f7441c6..e4bf6f2e4 100644
--- a/src/V3File.h
+++ b/src/V3File.h
@@ -100,7 +100,7 @@ private:
     stack<int>	m_parenVec;	// Stack of columns where last ( was
 
     int		endLevels(const char* strg);
-    static const char* indentStr(int levels);
+    const char* indentStr(int levels);
     void putcNoTracking(char chr);
 
 public:
diff --git a/src/V3Inst.cpp b/src/V3Inst.cpp
index d06d894d3..2645ab4a8 100644
--- a/src/V3Inst.cpp
+++ b/src/V3Inst.cpp
@@ -122,6 +122,12 @@ private:
 	nodep->unlinkFrBack()->deleteTree(); nodep=NULL;
     }
 
+    virtual void visit(AstUdpTable* nodep, AstNUser*) {
+	if (!v3Global.opt.bboxUnsup()) {
+	    nodep->v3error("Unsupported: Verilog 1995 UDP Tables.  Use --bbox-unsup to ignore tables.");
+	}
+    }
+
     // Save some time
     virtual void visit(AstNodeAssign*, AstNUser*) {}
     virtual void visit(AstAlways*, AstNUser*) {}
diff --git a/src/V3LinkResolve.cpp b/src/V3LinkResolve.cpp
index 2d0e3de83..d91c6d9dd 100644
--- a/src/V3LinkResolve.cpp
+++ b/src/V3LinkResolve.cpp
@@ -340,7 +340,8 @@ private:
     virtual void visit(AstUdpTable* nodep, AstNUser*) {
 	UINFO(5,"UDPTABLE  "<<nodep<<endl);
 	if (!v3Global.opt.bboxUnsup()) {
-	    nodep->v3error("Unsupported: Verilog 1995 UDP Tables.  Use --bbox-unsup to ignore tables.");
+	    // We don't warn until V3Inst, so that UDPs that are in libraries and
+	    // never used won't result in any warnings.
 	} else {
 	    // Massive hack, just tie off all outputs so our analysis can proceed
 	    AstVar* varoutp = NULL;
diff --git a/src/V3Options.cpp b/src/V3Options.cpp
index 8faa120db..c923d6820 100644
--- a/src/V3Options.cpp
+++ b/src/V3Options.cpp
@@ -660,6 +660,7 @@ void V3Options::parseOptsList(FileLine* fl, int argc, char** argv) {
 	    else if ( onoff   (sw, "-bbox-sys", flag/*ref*/) )	{ m_bboxSys = flag; }
 	    else if ( onoff   (sw, "-bbox-unsup", flag/*ref*/) ) { m_bboxUnsup = flag; }
 	    else if ( !strcmp (sw, "-cc") )			{ m_outFormatOk = true; m_systemC = false; m_systemPerl = false; }
+	    else if ( onoff   (sw, "-cdc", flag/*ref*/) )	{ m_cdc = flag; }
 	    else if ( onoff   (sw, "-coverage", flag/*ref*/) )	{ coverage(flag); }
 	    else if ( onoff   (sw, "-coverage-line", flag/*ref*/) ){ m_coverageLine = flag; }
 	    else if ( onoff   (sw, "-coverage-toggle", flag/*ref*/) ){ m_coverageToggle = flag; }
diff --git a/src/V3Options.h b/src/V3Options.h
index 18eb07489..ee5ea96f9 100644
--- a/src/V3Options.h
+++ b/src/V3Options.h
@@ -96,6 +96,7 @@ class V3Options {
     bool	m_autoflush;	// main switch: --autoflush
     bool	m_bboxSys;	// main switch: --bbox-sys
     bool	m_bboxUnsup;	// main switch: --bbox-unsup
+    bool	m_cdc;		// main switch: --cdc
     bool	m_coverageLine;	// main switch: --coverage-block
     bool	m_coverageToggle;// main switch: --coverage-toggle
     bool	m_coverageUser;	// main switch: --coverage-func
@@ -208,6 +209,7 @@ class V3Options {
     bool autoflush() const { return m_autoflush; }
     bool bboxSys() const { return m_bboxSys; }
     bool bboxUnsup() const { return m_bboxUnsup; }
+    bool cdc() const { return m_cdc; }
     bool coverage() const { return m_coverageLine || m_coverageToggle || m_coverageUser; }
     bool coverageLine() const { return m_coverageLine; }
     bool coverageToggle() const { return m_coverageToggle; }
diff --git a/src/Verilator.cpp b/src/Verilator.cpp
index 93b0d7f5b..8dab53bb2 100644
--- a/src/Verilator.cpp
+++ b/src/Verilator.cpp
@@ -50,6 +50,7 @@
 #include "V3EmitV.h"
 #include "V3Expand.h"
 #include "V3File.h"
+#include "V3Cdc.h"
 #include "V3Gate.h"
 #include "V3Graph.h"
 #include "V3GenClk.h"
@@ -352,6 +353,11 @@ void process () {
     V3Dead::deadifyAll(v3Global.rootp(), true);
     v3Global.rootp()->dumpTreeFile(v3Global.debugFilename("const.tree"));
 
+    // Clock domain crossing analysis
+    if (v3Global.opt.cdc()) {
+	V3Cdc::cdcAll(v3Global.rootp());
+    }
+
     // Reorder assignments in pipelined blocks
     if (v3Global.opt.oReorder()) {
 	V3Split::splitReorderAll(v3Global.rootp());
diff --git a/test_regress/t/t_cdc_async_bad.pl b/test_regress/t/t_cdc_async_bad.pl
new file mode 100755
index 000000000..6528c54ff
--- /dev/null
+++ b/test_regress/t/t_cdc_async_bad.pl
@@ -0,0 +1,25 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2009 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+
+compile (
+	 v_flags => ['--cdc --lint-only'],
+	 verilator_make_gcc => 0,
+	 fails => 1,
+	 expect=>
+'%Warning-CDCRSTLOGIC: t/t_cdc_async_bad.v:\d+: Logic in path that feeds async reset, via signal: TOP->v.rst2_bad_n
+%Warning-CDCRSTLOGIC: Use "/\* verilator lint_off CDCRSTLOGIC \*/" and lint_on around source to disable this message.
+%Warning-CDCRSTLOGIC:      See details in obj_dir/t_cdc_async_bad/Vt_cdc_async_bad__cdc.txt
+%Warning-CDCRSTLOGIC: t/t_cdc_async_bad.v:\d+: Logic in path that feeds async reset, via signal: TOP->v.rst3_bad_n
+%Error: Exiting due to.*',
+	 );
+
+file_grep ("$Self->{obj_dir}/V$Self->{name}__cdc.txt", qr/CDC Report/);
+
+ok(1);
+1;
diff --git a/test_regress/t/t_cdc_async_bad.v b/test_regress/t/t_cdc_async_bad.v
new file mode 100644
index 000000000..5587464b9
--- /dev/null
+++ b/test_regress/t/t_cdc_async_bad.v
@@ -0,0 +1,72 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2009 by Wilson Snyder.
+
+module t (/*AUTOARG*/
+   // Outputs
+   q0, q1, q2, q3, q4, q5,
+   // Inputs
+   clk, d, rst0_n
+   );
+   input clk;
+   input d;
+
+   // OK -- from primary
+   input rst0_n;
+   output wire  q0;
+   Flop flop0 (.q(q0), .rst_n(rst0_n), .clk(clk), .d(d));
+
+   // OK -- from flop
+   reg 	 rst1_n;
+   always @ (posedge clk) rst1_n <= rst0_n;
+   output wire  q1;
+   Flop flop1 (.q(q1), .rst_n(rst1_n), .clk(clk), .d(d));
+
+   // Bad - logic
+   wire  rst2_bad_n = rst0_n | rst1_n;
+   output wire  q2;
+   Flop flop2 (.q(q2), .rst_n(rst2_bad_n), .clk(clk), .d(d));
+
+   // Bad - logic in submodule
+   wire  rst3_bad_n;
+   Sub  sub (.z(rst3_bad_n), .a(rst0_n), .b(rst1_n));
+   output wire  q3;
+   Flop flop3 (.q(q3), .rst_n(rst3_bad_n), .clk(clk), .d(d));
+
+   // OK - bit selection
+   reg [3:0] rst4_n;
+   always @ (posedge clk) rst4_n <= {4{rst0_n}};
+   output wire  q4;
+   Flop flop4 (.q(q4), .rst_n(rst4_n[1]), .clk(clk), .d(d));
+
+   // Bad - logic, but waived
+   // verilator lint_off CDCRSTLOGIC
+   wire  rst5_waive_n = rst0_n & rst1_n;
+   // verilator lint_on CDCRSTLOGIC
+   output wire  q5;
+   Flop flop5 (.q(q5), .rst_n(rst5_waive_n), .clk(clk), .d(d));
+
+   initial begin
+      $display("%%Error: Not a runnable test");
+      $stop;
+   end
+
+endmodule
+
+module Flop (
+	     input clk,
+	     input d,
+	     input rst_n,
+	     output q);
+
+   always @ (posedge clk or negedge rst_n) begin
+      if (!rst_n) q <= 1'b0;
+      else q <= d;
+   end
+endmodule
+
+module Sub (input a, b,
+	    output z);
+   wire 	   z = a|b;
+endmodule