Add assertion for monotonic dump times #2103 (#2237)

docs/CONTRIBUTORS

@@ -28,6 +28,7 @@ Maciej Sobkowski
 Marco Widmer
 Matthew Ballance
 Mike Popoloski
+Nathan Myers
 Patrick Stewart
 Peter Monsson
 Philipp Wagner

include/verilated_fst_c.cpp

@@ -76,6 +76,7 @@ protected:
 VerilatedFst::VerilatedFst(void* fst)
     : m_fst(fst)
     , m_fullDump(true)
+    , m_minNextDumpTime(0)
     , m_nextCode(1)
     , m_scopeEscape('.')
     , m_symbolp(NULL) {
@@ -212,6 +213,12 @@ void VerilatedFst::addCallback(VerilatedFstCallback_t initcb, VerilatedFstCallba
 
 void VerilatedFst::dump(vluint64_t timeui) {
     if (!isOpen()) return;
+    if (timeui < m_minNextDumpTime) {
+      VL_PRINTF_MT("%%Warning: previous dump at t=%" VL_PRI64 "u, requesting t=%" VL_PRI64 "u\n",
+        m_minNextDumpTime - 1, timeui);
+      return;
+    }
+    m_minNextDumpTime = timeui + 1;
     if (VL_UNLIKELY(m_fullDump)) {
         m_fullDump = false;  // No more need for next dump to be full
         for (vluint32_t ent = 0; ent < m_callbacks.size(); ++ent) {

include/verilated_fst_c.h

@@ -48,6 +48,7 @@ private:
     void* m_fst;
     VerilatedAssertOneThread m_assertOne;  ///< Assert only called from single thread
     bool m_fullDump;
+    vluint64_t m_minNextDumpTime;
     vluint32_t m_nextCode;  ///< Next code number to assign
     char m_scopeEscape;
     std::string m_module;