Method parse

Marlin/src/gcode/parser.cpp:113–371

* Populate the command line state (command_letter, codenum, subcode, and string_arg) * by parsing a single line of G-Code. 58 bytes of SRAM are used to speed up seen/value. */

 * by parsing a single line of G-Code. 58 bytes of SRAM are used to speed up seen/value.
 */
void GCodeParser::parse(char *p) {

  reset(); // No codes to report

  auto uppercase = [](char c) {
    return TERN0(GCODE_CASE_INSENSITIVE, WITHIN(c, 'a', 'z')) ? c + 'A' - 'a' : c;
  };

  // Skip spaces
  while (*p == ' ') ++p;

  // Skip N[-0-9] if included in the command line
  if (uppercase(*p) == 'N' && NUMERIC_SIGNED(p[1])) {
    //TERN_(FASTER_GCODE_PARSER, set('N', p + 1)); // (optional) Set the 'N' parameter value
    p += 2;                  // skip N[-0-9]
    while (NUMERIC(*p)) ++p; // skip [0-9]*
    while (*p == ' ')   ++p; // skip [ ]*
  }

  // *p now points to the current command, which should be G, M, or T
  command_ptr = p;

  // Get the command letter, which must be G, M, or T
  const char letter = uppercase(*p++);

  // Nullify asterisk and trailing whitespace
  char *starpos = strchr(p, '*');
  if (starpos) {
    --starpos;                          // *
    while (*starpos == ' ') --starpos;  // spaces...
    starpos[1] = '\0';
  }

  #if ANY(MARLIN_DEV_MODE, SWITCHING_TOOLHEAD, MAGNETIC_SWITCHING_TOOLHEAD, ELECTROMAGNETIC_SWITCHING_TOOLHEAD)
    #define SIGNED_CODENUM 1
  #endif

  /**
   * Screen for good command letters.
   * With Realtime Reporting, commands S000, P000, and R000 are allowed.
   */
  #if ENABLED(REALTIME_REPORTING_COMMANDS)
    switch (letter) {
      case 'P': case 'R' ... 'S': {
        uint8_t digits = 0;
        char *a = p;
        while (*a++ == '0') digits++; // Count up '0' characters
        if (digits == 3) {            // Three '0' digits is a good command
          codenum = 0;
          command_letter = letter;
          return;
        }
      }
    }
  #endif

  /**
   * Screen for good command letters. G, M, and T are always accepted.