Merge pull request #1570 from C-o-r-E/escape_fix

Fixes gCode handling of comments and escaped characters

Documentation/GCodes.md

@@ -101,3 +101,25 @@
 *  M908 - Control digital trimpot directly.
 *  M928 - Start SD logging (M928 filename.g) - ended by M29
 *  M999 - Restart after being stopped by error
+
+# Comments
+
+Comments start at a `;` (semicolon) and end with the end of the line:
+
+    N3 T0*57 ; This is a comment
+    N4 G92 E0*67
+    ; So is this
+    N5 G28*22
+
+(example taken from the [RepRap wiki](http://reprap.org/wiki/Gcode#Comments))
+
+If you need to use a literal `;` somewhere (for example within `M117`), you can escape semicolons with a `\`
+(backslash):
+
+     M117 Hello \;)
+
+`\` can also be used to escape `\` itself, if you need a literal `\` in front of a `;`:
+
+    M117 backslash: \\;and a comment
+
+Please note that hosts should strip any comments before sending GCODE to the printer in order to save bandwidth.

Marlin/Marlin_main.cpp

@@ -730,16 +730,17 @@ void get_command()
     serial_char = MYSERIAL.read();
     if(serial_char == '\n' ||
        serial_char == '\r' ||
-       (serial_char == ':' && comment_mode == false) ||
        serial_count >= (MAX_CMD_SIZE - 1) )
     {
-      if(!serial_count) { //if empty line
-        comment_mode = false; //for new command
+      // end of line == end of comment
+      comment_mode = false;
+
+      if(!serial_count) {
+        // short cut for empty lines
         return;
       }
       cmdbuffer[bufindw][serial_count] = 0; //terminate string
-      if(!comment_mode){
-        comment_mode = false; //for new command
+
       fromsd[bufindw] = false;
       if(strchr(cmdbuffer[bufindw], 'N') != NULL)
       {
@@ -820,11 +821,20 @@ void get_command()
 
       bufindw = (bufindw + 1)%BUFSIZE;
       buflen += 1;
-      }
+
       serial_count = 0; //clear buffer
     }
-    else
-    {
+    else if(serial_char == '\\') {  //Handle escapes
+       
+        if(MYSERIAL.available() > 0  && buflen < BUFSIZE) {
+            // if we have one more character, copy it over
+            serial_char = MYSERIAL.read();
+            cmdbuffer[bufindw][serial_count++] = serial_char;
+        }
+
+        //otherwise do nothing        
+    }
+    else { // its not a newline, carriage return or escape char
         if(serial_char == ';') comment_mode = true;
         if(!comment_mode) cmdbuffer[bufindw][serial_count++] = serial_char;
     }