There are some ways of supporting chords with MML.
First of all, you should understand there are many schemes to support chords with this library.
As I wrote elsewhere, this library allows you only to parse MML text string, and it doesn't provide 'how to make a sound'.
For example, one of the ways is using 'C0E0G4' for C chord in C major.
The zero length notes are indicating the part of the chord.
Please see also my Super Mario example with Arduino!
static int get_note_frequency(const int note)
{
static const double BASEFREQ = 55.0;
return (int)(BASEFREQ * pow((double)2.0, (double)((double)(note - 9) / 12.0)));
}
static int get_note_length_ms(const int bpm, const int bticks, const int note_ticks)
{
return (60 * 1000) * note_ticks / bpm / bticks;
}