Int 2F Fn 1215  U - DOS 3+ Internal - Flush Buffer                         [D]

   AX = 1215h
   DS:DI -> disk buffer
   SS = DOS DS (must be using a DOS internal stack)
   STACK: WORD drives for which to skip buffer
       ignore buffer if drive same as high byte, or bytes differ and
       the buffer is for a drive OTHER than that given in low byte

Return: STACK unchanged

Note:  can be called only from within DOS

See Also: AX=1209h