Merge Implement M110 (PR#2327)

Marlin/Marlin_main.cpp

@@ -138,6 +138,7 @@
  * M109 - Sxxx Wait for extruder current temp to reach target temp. Waits only when heating
  *        Rxxx Wait for extruder current temp to reach target temp. Waits when heating and cooling
  *        IF AUTOTEMP is enabled, S<mintemp> B<maxtemp> F<factor>. Exit autotemp by any M109 without F
+ * M110 - Set the current line number
  * M111 - Set debug flags with S<mask>. See flag bits defined in Marlin.h.
  * M112 - Emergency stop
  * M114 - Output current position to serial port
@@ -791,8 +792,17 @@ void get_command() {
       char *npos = strchr(command, 'N');
       char *apos = strchr(command, '*');
       if (npos) {
+
+        boolean M110 = strstr_P(command, PSTR("M110")) != NULL;
+
+        if (M110) {
+          char *n2pos = strchr(command + 4, 'N');
+          if (n2pos) npos = n2pos;
+        }
+
         gcode_N = strtol(npos + 1, NULL, 10);
-        if (gcode_N != gcode_LastN + 1 && strstr_P(command, PSTR("M110")) == NULL) {
+
+        if (gcode_N != gcode_LastN + 1 && !M110) {
           gcode_line_error(PSTR(MSG_ERR_LINE_NO));
           return;
         }
@@ -807,7 +817,7 @@ void get_command() {
           }
           // if no errors, continue parsing
         }
-        else {
+        else if (npos == command) {
           gcode_line_error(PSTR(MSG_ERR_NO_CHECKSUM));
           return;
         }