diff --git a/.gitignore b/.gitignore
index 282ecc3..1de8357 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,6 +6,7 @@ test
 test_indep
 programSettings.txt
 EventBuilder
+DataGenerator
 
 data
 
diff --git a/DataGenerator.cpp b/DataGenerator.cpp
index 29df041..31b7ecf 100644
--- a/DataGenerator.cpp
+++ b/DataGenerator.cpp
@@ -1,4 +1,5 @@
 #include <cstdio>
+#include <random>
 
 #include "macro.h"
 #include "ClassDigitizer.h"
@@ -6,7 +7,53 @@
 
 int main(){
 
+  Digitizer * digi = new Digitizer();
+
+  Data * data = digi->GetData();
+
+  std::random_device rd;
+  std::mt19937 gen(rd());
+
+  std::uniform_int_distribution<int> RanNext(0, 1);
+  std::uniform_int_distribution<int> RanCh(1, 2);
+  std::uniform_int_distribution<unsigned short> RanEnergy(1, 1000);
+  std::uniform_int_distribution<unsigned long long> RanTime(1, 50);
+
+  int count = 0;
+  unsigned long long time = 0;
+  do{
+
+    int ch = RanCh(gen);
+    unsigned short energy = RanEnergy(gen);
+
+    unsigned long long timestamp = time + RanTime(gen) + RanNext(gen)*100;
+    time = timestamp;
+
+    count ++;
+
+    data->DataIndex[ch] ++;
+    int index = data->DataIndex[ch];
+
+    if( ch == 2 && index > 2) {
+      data->DataIndex[ch] --;
+      continue;
+    }
+    data->Energy[ch][index] = energy;
+    data->Timestamp[ch][index] = timestamp;
+
+    printf("%02d | %5d %10lld\n", ch, energy, time);
+
+  }while( count < 50 );
+
+  data->PrintAllData();
+
+  printf("===================================\n");
+
+  OnlineEventBuilder * eb = new OnlineEventBuilder(digi);
+
+  eb->BuildEvents(100);
 
 
+  delete digi;
 
 }
\ No newline at end of file
diff --git a/Makefile_test b/Makefile_test
index df50339..e2faead 100644
--- a/Makefile_test
+++ b/Makefile_test
@@ -14,7 +14,7 @@ ROOTLIBS = `root-config --cflags --glibs`
 
 OBJS = ClassDigitizer.o OnlineEventBuilder.o
 
-ALL = test test_indep EventBuilder
+ALL = test test_indep EventBuilder DataGenerator
 
 #########################################################################
 
@@ -40,3 +40,7 @@ test_indep : test_indep.cpp RegisterAddress.h macro.h
 EventBuilder : EventBuilder.cpp ClassData.h
 		@echo "--------- making EventBuilder"
 		$(CC) $(COPTS) -o EventBuilder EventBuilder.cpp $(CAENLIBS) $(ROOTLIBS) 
+
+DataGenerator : DataGenerator.cpp ClassDigitizer.o  OnlineEventBuilder.o
+		@echo "--------- making DataGenerator"
+		$(CC) $(COPTS) -o DataGenerator DataGenerator.cpp ClassDigitizer.o  OnlineEventBuilder.o $(CAENLIBS)
diff --git a/OnlineEventBuilder.cpp b/OnlineEventBuilder.cpp
index c3ba564..c693011 100644
--- a/OnlineEventBuilder.cpp
+++ b/OnlineEventBuilder.cpp
@@ -1,5 +1,7 @@
 #include "OnlineEventBuilder.h"
 
+#include <algorithm>
+
 OnlineEventBuilder::OnlineEventBuilder(Digitizer * digi){
 
   data = digi->GetData();
@@ -29,10 +31,8 @@ OnlineEventBuilder::~OnlineEventBuilder(){
 
 void OnlineEventBuilder::FindEarlistTimeAndCh(){
 
-  if( isNeverBuild ){
-    earlistTime = -1;
-    earlistCh = -1;
-  }
+  earlistTime = -1;
+  earlistCh = -1;
 
   nExhaushedCh = 0;
   for( int i = 0; i < MaxNChannels; i++ ){
@@ -53,14 +53,14 @@ void OnlineEventBuilder::FindEarlistTimeAndCh(){
     if( time < earlistTime ) {
       earlistTime = time;
       earlistCh = ch;
-      printf("ch: %d , nextIndex : %d, %llu\n", ch, nextIndex[ch] , earlistTime);
+      //printf("ch: %d , nextIndex : %d, %llu\n", ch, nextIndex[ch] , earlistTime);
     }
   }
 
 }
 
 
-void OnlineEventBuilder::BuildEvents(unsigned short timeWindow){
+void OnlineEventBuilder::BuildEvents(unsigned short timeWindow, bool verbose = false){
 
   this->timeWindow = timeWindow;
 
@@ -109,33 +109,35 @@ void OnlineEventBuilder::BuildEvents(unsigned short timeWindow){
 
     }
 
+
     isNeverBuild = false;
 
-    //===== print
+    std::sort(events[eventIndex].begin(), events[eventIndex].end(), [](const dataPoint& a, const dataPoint& b) {
+      return a.timeStamp < b.timeStamp;
+    });
     
-    printf("######################################### Event ID : %ld\n", eventIndex);
-    for( int i = 0; i <(int) events[eventIndex].size(); i++){
-      printf("%02d | %5d %llu \n", events[eventIndex][i].ch, events[eventIndex][i].energy, events[eventIndex][i].timeStamp); 
+    if( verbose ){
+    //===== print
+      printf("&&&&&&&&&&&&&&&&&&&&&&&&& Event ID : %ld\n", eventIndex);
+      for( int i = 0; i <(int) events[eventIndex].size(); i++){
+        printf("%02d | %5d %llu \n", events[eventIndex][i].ch, events[eventIndex][i].energy, events[eventIndex][i].timeStamp); 
+      }
     }
 
 
     ///Find the next earlist 
-    earlistTime = data->Timestamp[dp.ch][nextIndex[dp.ch]];
     FindEarlistTimeAndCh();
 
-    if( nExhaushedCh == nCh ) {
-      printf("######################### no more eevent to be built\n"); 
-      break;
+    if( verbose ){
+      if( nExhaushedCh == nCh ) {
+        printf("######################### no more eevent to be built\n"); 
+        break;
+      }  
+      printf("----- next ch : %d, next earlist Time : %llu \n", earlistCh, earlistTime);
     }
-    
-    printf("----- next ch : %d, next earlist Time : %llu \n", earlistCh, earlistTime);
 
   }while(nExhaushedCh < nCh);
 
-  for( unsigned int i = 0; i < nCh; i ++ ) printf("%d | exhaushed ? %d \n", i, chExhaused[i] ); 
-  printf("------ nExhaushedCh = %d \n", nExhaushedCh);
-
-
   //TODO ----- to speed up continue with data->DataIndex
   data->ClearData();
   for( int i = 0 ; i < MaxNChannels; i++) nextIndex[i] = -1;
diff --git a/OnlineEventBuilder.h b/OnlineEventBuilder.h
index 589c839..fd90c60 100644
--- a/OnlineEventBuilder.h
+++ b/OnlineEventBuilder.h
@@ -28,7 +28,7 @@ public:
   OnlineEventBuilder(Digitizer * digi);
   ~OnlineEventBuilder();
 
-  void BuildEvents(unsigned short timeWindow);
+  void BuildEvents(unsigned short timeWindow, bool verbose = false);
 
   long eventIndex;
   std::vector<dataPoint> events[MaxNEvent]; // should be a cirular memory, store energy