Int 15 Fn 1019  - Topview - "sound" - Make Tone                            [Q]

   AX = 1019h
   BX = frequency in Hertz (0000h = silence)
   CX = duration in clock ticks (18.2 ticks/sec)

Return: immediately, tone continues to completion

Notes: if another tone is already playing, the new tone does not start until
     completion of the previous one.  Up to 32 tones may be queued before
     the process is blocked until a note completes.
   in DV 2.00, the lowest tone allowed is 20 Hz
   if CX = 0, the current note is cancelled; if BX = 0 as well, all queued
     notes are also cancelled

See Also: INT 16/AH=73h