Diff: PPP-Blinky/ppp-blinky.cpp

Revision:

145:098b6ed2f7f2

Parent:

144:01d98cf7738e

Child:

146:a45f49a2b29c

--- a/PPP-Blinky/ppp-blinky.cpp	Tue Aug 29 18:42:20 2017 +0000
+++ b/PPP-Blinky/ppp-blinky.cpp	Tue Aug 29 18:57:04 2017 +0000
@@ -157,7 +157,7 @@
 struct pppType {
     int online; // we hunt for a PPP connection if this is zero
     int hostIP; // ip address of host
-    int crc; // for calculating IP and TCP CRCs
+    int fcs; // PPP "frame check sequence" - a 16-bit HDLC-like checksum used in all PPP frames
     int ledState; // state of LED1
     int httpPageCount;
     int firstFrame; // cleared after first frame
@@ -270,28 +270,28 @@
     if ( pc.readable() ) putsWhileCheckingInput( "Character available!\n" );
 }
 
-/// Initialize the PPP CRC total
-void crcReset()
+/// Initialize the PPP FCS (frame check sequence) total
+void fcsReset()
 {
-    ppp.crc=0xffff;   // crc restart
+    ppp.fcs=0xffff;   // crc restart
 }
 
-/// update the cumulative PPP CRC
-void crcDo(int x)
+/// update the cumulative PPP FCS (frame check sequence)
+void fcsDo(int x)
 {
     for (int i=0; i<8; i++) {
-        ppp.crc=((ppp.crc&1)^(x&1))?(ppp.crc>>1)^0x8408:ppp.crc>>1; // crc calculator
+        ppp.fcs=((ppp.fcs&1)^(x&1))?(ppp.fcs>>1)^0x8408:ppp.fcs>>1; // crc calculator
         x>>=1;
     }
     checkPc(); // handle input
 }
 
-/// calculate the PPP CRC on an entire block of memory
-int crcBuf(char * buf, int size) // crc on an entire block of memory
+/// calculate the PPP FCS (frame check sequence) on an entire block of memory
+int fcsBuf(char * buf, int size) // crc on an entire block of memory
 {
-    crcReset();
-    for(int i=0; i<size; i++)crcDo(*buf++);
-    return ppp.crc;
+    fcsReset();
+    for(int i=0; i<size; i++)fcsDo(*buf++);
+    return ppp.fcs;
 }
 
 /// Get one character from our received PPP buffer
@@ -329,7 +329,7 @@
     if(start==end) {
         return; // empty frame
     }
-    crcReset();
+    fcsReset();
     char * dest = ppp.pkt.buf;
     ppp.pkt.len=0;
     int unstuff=0;
@@ -342,19 +342,19 @@
                 *dest = ppp.rx.buf[idx];
                 ppp.pkt.len++;
                 dest++;
-                crcDo(ppp.rx.buf[idx]);
+                fcsDo(ppp.rx.buf[idx]);
             }
         } else { // unstuff characters prefixed with 0x7d
             *dest = ppp.rx.buf[idx]^0x20;
             ppp.pkt.len++;
             dest++;
-            crcDo(ppp.rx.buf[idx]^0x20);
+            fcsDo(ppp.rx.buf[idx]^0x20);
             unstuff=0;
         }
         idx = (idx+1) & (RXBUFLEN-1);
         if (idx == end) break;
     }
-    ppp.pkt.crc = ppp.crc & 0xffff;
+    ppp.pkt.crc = ppp.fcs & 0xffff;
     if(0) dumpPPPFrame(); // set to 1 to dump ALL ppp frames
     if (ppp.pkt.crc == 0xf0b8) { // check for good CRC
         determinePacketType();
@@ -393,7 +393,7 @@
 /// send a PPP frame in HDLC format
 void sendPppFrame()
 {
-    int crc = crcBuf(ppp.pkt.buf, ppp.pkt.len-2); // update crc
+    int crc = fcsBuf(ppp.pkt.buf, ppp.pkt.len-2); // update crc
     ppp.pkt.buf[ ppp.pkt.len-2 ] = (~crc>>0); // fcs lo (crc)
     ppp.pkt.buf[ ppp.pkt.len-1 ] = (~crc>>8); // fcs hi (crc)
     pcPutcWhileCheckingInput(0x7e); // hdlc start-of-frame "flag"