Diff: PPP-Blinky/ppp-blinky.cpp

Revision:

170:3d3b2126181c

Parent:

169:ee90aed3a735

Child:

171:46b36d4edd1d

--- a/PPP-Blinky/ppp-blinky.cpp	Mon Sep 04 04:28:55 2017 +0000
+++ b/PPP-Blinky/ppp-blinky.cpp	Mon Sep 04 05:45:59 2017 +0000
@@ -546,6 +546,19 @@
     memcpy(ipDstPort,tempHold, 2); // dest <- tempHold
 }
 
+/// Build the "pseudo header" required for UDP and TCP, then calculate its checksum
+void checkSumPseudoHeader( unsigned int packetLength )
+{
+    // this header  contains the most important parts of the IP header, i.e. source and destination address, protocol number and data length.
+    pseudoIpHeaderType pseudoHeader; // create pseudo header
+    pseudoHeader.srcAdrR = ppp.ip->srcAdrR; // copy in ip source address
+    pseudoHeader.dstAdrR = ppp.ip->dstAdrR; // copy in ip dest address
+    pseudoHeader.zero = 0; // zero byte
+    pseudoHeader.protocol = ppp.ip->protocol; // protocol number (udp or tcp)
+    pseudoHeader.lengthR = __REV16( packetLength ); // size of tcp or udp packet
+    dataCheckSum(pseudoHeader.start, 12, 1); // calculate this header's checksum
+}
+
 /// Process an incoming UDP packet.
 /// If the packet starts with the string "echo " or "test" we echo back a special packet
 void UDPpacket()
@@ -598,14 +611,13 @@
         swapIpPorts(); // swap IP source and destination ports
         if (echoFound) {
             memcpy(ppp.udp->data,"Got{",4); // in the UDP data modify "echo" to "Got:"
-            int n = sprintf(ppp.udp->data+udpLength.data, "} UDP Server: PPP-Blinky\n"); // an appendix
+            int n=0;
+            n=n+sprintf(n+ppp.udp->data+udpLength.data, "} UDP Server: PPP-Blinky\n"); // an appendix
             udpLength.data = udpLength.data + n; // update udp data size with the size of the appendix
         }
         if (testFound) {
-            char udpResponse[50];
-            int n = 0;
-            n = n+sprintf(udpResponse+n,"Response count %d\n",ppp.responseCounter++);
-            memcpy(ppp.udp->data,udpResponse,n); // copy response to the UDP data area
+            int n=0;
+            n=n+sprintf(n+ppp.udp->data,"Response count %d\n",ppp.responseCounter++);
             udpLength.data = n; // update udp data size
         }
         // we may have changed data length, update all the lengths
@@ -616,7 +628,10 @@
         ppp.pkt.len      = ipLength.all+2+4; // update ppp packet length
 
         IpHeaderCheckSum();  // refresh IP header checksum
-        ppp.udp->checkSumR = 0; // we don't yet recompute the UDP checksum (it's optional), so have to zero it
+        checkSumPseudoHeader( udpLength.all ); // get the UDP pseudo-header checksum
+        ppp.udp->checksumR = 0; // before TCP checksum calculations the checksum bytes must be set cleared
+        unsigned int pseudoHeaderSum=dataCheckSum(ppp.udpStart,udpLength.all, 0); // continue the TCP checksum on the whole TCP packet
+        ppp.udp->checksumR = __REV16( pseudoHeaderSum); // tcp checksum done, store it in the TCP header
         ppp.responseCounter++; // count UDP packet as a response
         sendPppFrame(); // send the UDP message back
     } else {
@@ -997,22 +1012,14 @@
 
     // the header is all set up, now do the IP and TCP checksums
     IpHeaderCheckSum(); // calculate new IP header checksum
-
-    // create the TCP "pseudo-header" (containing some IP header values) in order to correctly calculate the TCP checksum
-    // this header  contains the most important parts of the IP header, i.e. source and destination address, protocol number and data length.
-    pseudoIpHeaderType pseudoHeader; // create pseudo header
-    pseudoHeader.srcAdrR = ppp.ip->srcAdrR; // copy in ip source address
-    pseudoHeader.dstAdrR = ppp.ip->dstAdrR; // copy in ip dest address
-    pseudoHeader.zero = 0; // padding
-    pseudoHeader.protocol = ppp.ip->protocol; // protocol number
-    pseudoHeader.lengthR = __REV16( tcpSize ); // size of tcp packet
-    dataCheckSum(pseudoHeader.start, 12, 1); // start with the TCP checksum of the pseudoheader
+    checkSumPseudoHeader( tcpSize ); // get the TCP pseudo-header checksum
     ppp.tcp->checksumR = 0; // before TCP checksum calculations the checksum bytes must be set cleared
     unsigned int pseudoHeaderSum=dataCheckSum(ppp.tcpStart,tcpSize, 0); // continue the TCP checksum on the whole TCP packet
     ppp.tcp->checksumR = __REV16( pseudoHeaderSum); // tcp checksum done, store it in the TCP header
 
-    dumpHeaderIP(1); // dump outgoing IP header
-    dumpHeaderTCP(1); // dump outgoing TCP header
+    dumpHeaderIP(1); // dump outgoing IP header before sending the frame
+    dumpHeaderTCP(1); // dump outgoing TCP header before sending the frame
+    
     for (int i=0; i<45*1000/10; i++) { // 45 ms delay before sending frame - a typical internet delay time
         checkPc(); // catch any incoming characters
         wait_us(10); // wait less than 1 character duration at 115200