Do_Sound ($F289)

This routine will start/continue making the sound which was first set up by your call to Init_Music. This routine should normally be called right after your call to Wait_Recal. It takes the next music information, contained in the music buffer $C83F-$C84C, and updates only those registers which differ from the last data written to the sound chip.

ENTRY:

DP = $D0

EXIT:

D-reg, X-reg, U-reg trashed

Source