Meade LX200 commands Sr and Sd have extra space and wrong degree character

[Peter]

This was found from experiments with a telescope emulator supporting the Meade LX-200 protocol, using the slew command (CMD+0) from within Stellarium 0.12.4 on the Mac.

The current behaviour does not match the documented protocol,
http://www.meade.com/support/TelescopeProtocol_2010-10.pdf
http://www.meade.com/support/LX200CommandSet.pdf

This was confirmed by reading https://svn.code.sf.net/p/stellarium/code/trunk/stellarium/plugins/TelescopeControl/src/servers/Lx200Command.cpp which is quoted below with comments on three problem lines.

bool Lx200CommandSetSelectedRa::writeCommandToBuffer(char *&p, char *end)
{
 if (end-p < 13) return false;
   // set object ra:
 *p++ = ':';
 *p++ = 'S';
 *p++ = 'r';
 *p++ = ' '; // REMOVE THIS?
 int x = ra;
 p += 8;
 p[-1] = '0' + (x % 10); x /= 10;
 p[-2] = '0' + (x % 6); x /= 6;
 p[-3] = ':';
 p[-4] = '0' + (x % 10); x /= 10;
 p[-5] = '0' + (x % 6); x /= 6;
 p[-6] = ':';
 p[-7] = '0' + (x % 10); x /= 10;
 p[-8] = '0' + x;
 *p++ = '#';
 has_been_written_to_buffer = true;
 return true;
}

i.e. This sends ":Sr HH:MM:SS#" with a space after the "Sr" before the first digit. The protocol specifies sending ":SrHH:MM.T#" or ":SrHH:MM:SS#" with no space after the "Sr".

bool Lx200CommandSetSelectedDec::writeCommandToBuffer(char *&p, char *end)
{
 if (end-p < 13)
  return false;

   // set object dec:
 *p++ = ':';
 *p++ = 'S';
 *p++ = 'd';
 *p++ = ' '; // REMOVE THIS?
 int x = dec;
 if (x < 0)
 {
  *p++ = '-';
  x = -x;
 }
 else
 {
  *p++ = '+';
 }
 p += 8;
 p[-1] = '0' + (x % 10); x /= 10;
 p[-2] = '0' + (x % 6); x /= 6;
 p[-3] = ':';
 p[-4] = '0' + (x % 10); x /= 10;
 p[-5] = '0' + (x % 6); x /= 6;
 p[-6] = 223; // degree symbol <-- SHOULD BE '*' INSTEAD, i.e. chr(42)
 p[-7] = '0' + (x % 10); x /= 10;
 p[-8] = '0' + x;
 *p++ = '#';
 has_been_written_to_buffer = true;
 return true;
}

i.e. This sends ":Sd sDD?MM:SS#" with a space after the "Sd" before the first digit, where ? represents chr(223).

The protocol specifies sending ":SdsDD*MM#" or ":SdsDD*MM:SS#" where the second "s" means the sign, plus or minus. Rather than a degree symbol, it should be asterisk, chr(42).

This should be a three line fix - the hard part will be testing with a few real telescopes claiming to support the Meade LX-200 protocol.

[Alexander Wolf (alexwolf)]

Diff: http://bazaar.launchpad.net/~stellarium/stellarium/trunk/revision/6529