diff --git a/beidou.cc b/beidou.cc
index cb8f78e..8b2106e 100644
--- a/beidou.cc
+++ b/beidou.cc
@@ -1,13 +1,57 @@
 #include "beidou.hh"
 #include "bits.hh"
+#include <iostream>
+using namespace std;
+
+// with immense gratitude to https://stackoverflow.com/questions/24612436/how-to-check-a-bch15-11-1-code-checksum-for-bds-beidou-satellite-system
+
+static int checkbds(int bits)
+{
+  static int const at[15] = {1, 2, 4, 8, 3, 6, 12, 11, 5, 10, 7, 14, 15, 13, 9};
+  int s, i, j;
+
+  for(i = 1; i <= 2; i++)
+  {
+    s = 0;
+    for(j = 0; j < 15; j++)
+    {
+      if(bits & (1<<j))
+      {
+        s ^= at[(i * j) % 15];
+      }
+    }
+    if(s != 0)
+    {
+      return 0;
+    }
+  }
+  return 1;
+}
 
 std::basic_string<uint8_t> getCondensedBeidouMessage(std::basic_string_view<uint8_t> payload)
 {
+
+  // payload consists of 32 bit words where we have to ignore the first 2 bits of every word
+
+  int chunk = getbitu(&payload[0], 17, 15);
+  //  cout <<"w0 checkbds(chunk0): "<<checkbds(chunk) << endl;
+  if(!checkbds(chunk))
+    throw std::runtime_error("Beidou checksum error chunk0");
+  
   uint8_t buffer[(26+9*22)/8];
 
   setbitu(buffer, 0, 26, getbitu(&payload[0], 2, 26));
   
   for(int w = 1 ; w < 10; ++w) {
+    int chunk1 = getbitu(&payload[0], 2+w*32, 11);
+    int chunk2 = getbitu(&payload[0], 2+w*32+11, 11);
+    int parity1 = getbitu(&payload[0], 2+w*32+22, 4);
+    int parity2 = getbitu(&payload[0], 2+w*32+22+4, 4);
+    chunk1 = (chunk1<<4) | parity1;
+    chunk2 = (chunk2<<4) | parity2;
+    //cout <<"w"<<w<<" checkbds(chunk1): "<<checkbds(chunk1) << ", checkbds(chunk2): "<<checkbds(chunk2)<<endl;
+    if(!checkbds(chunk1) || !checkbds(chunk2))
+      throw std::runtime_error("Beidou checksum error");
     setbitu(buffer, 26+22*(w-1), 22, getbitu(&payload[0], 2 + w*32, 22));
   }
 
diff --git a/beidou.hh b/beidou.hh
index 8413b23..d144fbd 100644
--- a/beidou.hh
+++ b/beidou.hh
@@ -8,6 +8,16 @@
 std::basic_string<uint8_t> getCondensedBeidouMessage(std::basic_string_view<uint8_t> payload);
 int beidouBitconv(int their);
 
+/* Geostationary, so D2, so not to be parsed by this parser:
+   C01 (140E)
+   C02 (80E)
+   C03 (110.5E)
+   C04 (160E)
+   C05 (58.75E)
+*/
+
+
+
 
 struct BeidouMessage
 {
diff --git a/navdump.cc b/navdump.cc
index 378ddde..c70e65c 100644
--- a/navdump.cc
+++ b/navdump.cc
@@ -36,14 +36,43 @@ static std::string humanTime(time_t t)
 }
 
 
+string beidouHealth(int in)
+{
+  string ret;
+  if(in == 256) {
+    return "NO CLOCK";
+  }
+  if(in==511) {
+    return "NO SAT";
+  }
+
+  if(in & (1<<7))
+    ret += "B1I abnormal ";
+  if(in & (1<<6))
+    ret += "B2I abnormal ";
+  if(in & (1<<5))
+    ret += "B3I abnormal ";
+  if(in & (1<<1))
+    ret += "navigation abnormal ";
+
+  if(ret.empty())
+    return "OK";
+  return ret;
+}
+
 int main(int argc, char** argv)
 {
   for(;;) {
     char bert[4];
-    if(read(0, bert, 4) != 4 || bert[0]!='b' || bert[1]!='e' || bert[2] !='r' || bert[3]!='t') {
-      cerr<<"EOF or bad magic"<<endl;
+    int res = read(0, bert, 4);
+    if( res != 4) {
+      cerr<<"EOF, res = "<<res<<endl;
       break;
     }
+    if(bert[0]!='b' || bert[1]!='e' || bert[2] !='r' || bert[3]!='t') {
+      cerr<<"Bad magic"<<endl;
+    }
+  
     
     uint16_t len;
     if(read(0, &len, 2) != 2)
@@ -58,7 +87,7 @@ int main(int argc, char** argv)
     cout<<humanTime(nmm.localutcseconds())<<" "<<nmm.localutcnanoseconds()<<" ";
     cout<<"src "<<nmm.sourceid()<< " ";
     if(nmm.type() == NavMonMessage::ReceptionDataType) {
-      cout<<"receptiondata for "<<nmm.rd().gnssid()<<","<<nmm.rd().gnsssv()<<endl;
+      cout<<"receptiondata for "<<nmm.rd().gnssid()<<","<<nmm.rd().gnsssv()<<", db "<<nmm.rd().db()<<" ele "<<nmm.rd().el() <<" azi "<<nmm.rd().azi()<<endl;
     }
     else if(nmm.type() == NavMonMessage::GalileoInavType) {
       basic_string<uint8_t> inav((uint8_t*)nmm.gi().contents().c_str(), nmm.gi().contents().size());
@@ -109,17 +138,51 @@ int main(int argc, char** argv)
       }
       cout<<"\n";
     }
-    else if(nmm.type() == NavMonMessage::BeidouInavType) {
-      int sv = nmm.bi().gnsssv();
-      auto cond = getCondensedBeidouMessage(std::basic_string<uint8_t>((uint8_t*)nmm.bi().contents().c_str(), nmm.bi().contents().size()));
+    else if(nmm.type() == NavMonMessage::BeidouInavTypeD1) {
+      int sv = nmm.bid1().gnsssv();
+      auto cond = getCondensedBeidouMessage(std::basic_string<uint8_t>((uint8_t*)nmm.bid1().contents().c_str(), nmm.bid1().contents().size()));
       BeidouMessage bm;
       uint8_t pageno;
       int fraid = bm.parse(cond, &pageno);
       cout<<"BeiDou "<<sv<<": "<<bm.sow<<", FraID "<<fraid;
-      if(fraid == 1)
-        cout<<" wn "<<bm.wn<<" t0c "<<(int)bm.t0c<<" aodc "<< (int)bm.aodc <<" aode "<< (int)bm.aode <<" sath1 "<< (int)bm.sath1 << endl;
-      cout<<endl;
+      if(fraid == 1) {
+        cout<<" wn "<<bm.wn<<" t0c "<<(int)bm.t0c<<" aodc "<< (int)bm.aodc <<" aode "<< (int)bm.aode <<" sath1 "<< (int)bm.sath1 << " urai "<<(int)bm.urai << " af0 "<<bm.a0 <<" af1 " <<bm.a1<<endl;
+      }
+      else if(fraid == 4 && 1<= pageno && pageno <= 24) {
+        cout <<" pageno "<< (int) pageno<<" AmEpID "<< getbitu(&cond[0], beidouBitconv(291), 2);
+      }
+      else if(fraid == 5 && 1<= pageno && pageno <= 6) {
+        cout <<" pageno "<<(int)pageno<<" AmEpID "<< getbitu(&cond[0], beidouBitconv(291), 2);
+      }
 
+      else if(fraid == 5 && pageno==7) {
+        for(int n=0; n<19; ++n)
+          cout<<" hea"<<(1+n)<<" " << getbitu(&cond[0], beidouBitconv(51+n*9), 9) << " ("<<beidouHealth(getbitu(&cond[0], beidouBitconv(51+n*9), 9)) <<")";
+      }
+      
+      else if(fraid == 5 && pageno==8) {
+        for(int n=0; n<10; ++n)
+          cout<<" hea"<<(20+n)<<" " << getbitu(&cond[0], beidouBitconv(51+n*9), 9) << " ("<<beidouHealth(getbitu(&cond[0], beidouBitconv(51+n*9), 9))<<")";
+        cout<<" WNa "<<getbitu(&cond[0], beidouBitconv(190), 8)<<" t0a "<<getbitu(&cond[0], beidouBitconv(198), 8);
+      }
+      else if(fraid == 5 && pageno==24) {
+        int AmID= getbitu(&cond[0], beidouBitconv(216), 2);
+        cout<<" AmID "<< AmID;
+        for(int n=0; n<14; ++n)
+          cout<<" hea"<<(31+n)<<" (" << getbitu(&cond[0], beidouBitconv(51+n*9), 9) << " "<<beidouHealth(getbitu(&cond[0], beidouBitconv(51+n*9), 9))<<")";
+      }
+      cout<<endl;
+      
+    }
+    else if(nmm.type() == NavMonMessage::BeidouInavTypeD2) {
+      int sv = nmm.bid2().gnsssv();
+      auto cond = getCondensedBeidouMessage(std::basic_string<uint8_t>((uint8_t*)nmm.bid2().contents().c_str(), nmm.bid2().contents().size()));
+      BeidouMessage bm;
+      uint8_t pageno;
+      int fraid = bm.parse(cond, &pageno);
+
+      cout<<"BeiDou "<<sv<<" D2: "<<bm.sow<<", FraID "<<fraid << endl;
+            
     }
     else if(nmm.type() == NavMonMessage::ObserverPositionType) {
       cout<<"ECEF"<<endl;
diff --git a/navmon.proto b/navmon.proto
index 9778def..bebb080 100644
--- a/navmon.proto
+++ b/navmon.proto
@@ -7,8 +7,9 @@ message NavMonMessage {
     GalileoInavType = 3;
     RFDataType = 4;
     GPSInavType = 5;
-    BeidouInavType = 6;
-    GLONASSInavType = 7;            
+    BeidouInavTypeD1 = 6;
+    GLONASSInavType = 7;
+    BeidouInavTypeD2 = 8;    
   }
 
   required uint64 sourceID = 1;
@@ -35,7 +36,15 @@ message NavMonMessage {
 	required bytes contents =5;
   }
 
-  message BeidouInav {
+  message BeidouInavD1 {
+	required uint32 gnssWN =1;
+  	required uint32 gnssTOW =2; // INTEGERS!
+
+	required uint32 gnssID =3;
+	required uint32 gnssSV =4;
+	required bytes contents =5;
+  }
+  message BeidouInavD2 {
 	required uint32 gnssWN =1;
   	required uint32 gnssTOW =2; // INTEGERS!
 
@@ -81,5 +90,6 @@ message NavMonMessage {
   optional RFData rfd=7;
   optional ObserverPosition op=8;
   optional GPSInav gpsi=9;
-  optional BeidouInav bi=10;    
+  optional BeidouInavD1 bid1=10;
+  optional BeidouInavD2 bid2=11;      
 }
diff --git a/ubxtool.cc b/ubxtool.cc
index 2147019..60dd173 100644
--- a/ubxtool.cc
+++ b/ubxtool.cc
@@ -188,16 +188,11 @@ std::pair<UBXMessage, struct timeval> getUBXMessage(int fd)
       readn2(fd, b, 4);
       msg.append(b, 4); // class, type, len1, len2
 
-
-      
-
       uint16_t len = b[2] + 256*b[3];
       //      cerr<<"Got class "<<(int)msg[2]<<" type "<<(int)msg[3]<<", len = "<<len<<endl;
       uint8_t buffer[len+2];
       res=readn2(fd, buffer, len+2);
 
-
-      
       msg.append(buffer, len+2); // checksum
       if(!g_fromFile)
         writen2(logfile, msg.c_str(), msg.size());      
@@ -260,10 +255,13 @@ void emitNMM(int fd, const NavMonMessage& nmm)
             
   string out;
   nmm.SerializeToString(& out);
-  writen2(fd, "bert", 4);
+  string msg("bert");
+  
   uint16_t len = htons(out.size());
-  writen2(fd, &len, 2);
-  writen2(fd, out.c_str(), out.size());
+  msg.append((char*)&len, 2);
+  msg.append(out);
+  
+  writen2(fd, msg.c_str(), msg.size());
 }
 
 void enableUBXMessageUSB(int fd, uint8_t ubxClass, uint8_t ubxType, uint8_t rate=1)
@@ -621,9 +619,9 @@ int main(int argc, char** argv)
         };
         pos p;
         memcpy(&p, payload.c_str(), sizeof(pos));
-        cerr<<"Position: ("<< p.ecefX / 100000.0<<", "
+        /*        cerr<<"Position: ("<< p.ecefX / 100000.0<<", "
             << p.ecefY / 100000.0<<", "
-            << p.ecefZ / 100000.0<<") +- "<<p.pAcc<<" cm"<<endl;
+            << p.ecefZ / 100000.0<<") +- "<<p.pAcc<<" cm"<<endl;*/
 
 //        g_ourpos = {p.ecefX/100.0, p.ecefY/100.0, p.ecefZ/100.0};
         
@@ -746,15 +744,26 @@ int main(int argc, char** argv)
               continue;
             }
             NavMonMessage nmm;
-            nmm.set_type(NavMonMessage::BeidouInavType);
             nmm.set_localutcseconds(g_gstutc.tv_sec);
             nmm.set_localutcnanoseconds(g_gstutc.tv_nsec);
-            nmm.set_sourceid(g_srcid);         
-            nmm.mutable_bi()->set_gnsswn(bm.wn);  
-            nmm.mutable_bi()->set_gnsstow(bm.sow); 
-            nmm.mutable_bi()->set_gnssid(id.first);
-            nmm.mutable_bi()->set_gnsssv(id.second);
-            nmm.mutable_bi()->set_contents(string((char*)gstr.c_str(), gstr.size()));
+            nmm.set_sourceid(g_srcid);
+            if(id.second > 5) {
+              // this **HARDCODES** that C01,02,03,04,05 emit D2 messages!            
+              nmm.set_type(NavMonMessage::BeidouInavTypeD1);
+              nmm.mutable_bid1()->set_gnsswn(bm.wn);  
+              nmm.mutable_bid1()->set_gnsstow(bm.sow); 
+              nmm.mutable_bid1()->set_gnssid(id.first);
+              nmm.mutable_bid1()->set_gnsssv(id.second);
+              nmm.mutable_bid1()->set_contents(string((char*)gstr.c_str(), gstr.size()));
+            }
+            else {
+              nmm.set_type(NavMonMessage::BeidouInavTypeD2);
+              nmm.mutable_bid2()->set_gnsswn(bm.wn);  
+              nmm.mutable_bid2()->set_gnsstow(bm.sow); 
+              nmm.mutable_bid2()->set_gnssid(id.first);
+              nmm.mutable_bid2()->set_gnsssv(id.second);
+              nmm.mutable_bid2()->set_contents(string((char*)gstr.c_str(), gstr.size()));
+            }
             emitNMM(1, nmm);
             continue;
           }