Function 0Fh	ESDI Format Unit Periodic Interrupt	(PS/2 50, 60, 80)
entry   AH      0Fh 
	AL      phase code 
		00h     reserved 
		01h     surface analysis 
		02h     formatting 
return  CF      clear   if formatting should continue 
		set     if it should terminate 
note    1) Called during ESDI drive formatting after each cylinder is completed 
	2) The ROM BIOS default handler for this function returns with the 
	   carry flag set.
	3) This function call can be captured by a program so that it will be 
	   notified as each cylinder is formatted or analyzed. The program can
	   count interrupts for each phase to determine the current cylinder 
	   number.