)
Call European MS-DOS 4.0 device helper function with:
	DL = function
	    00h "SchedClock" called on each timer tick
		AL = tick interval in milliseconds
	    01h "DevDone" device I/O complete
		ES:BX -> request header
		Note:	must update status word first; may be called from
			  an interrupt handler
	    02h "PullRequest" pull next request from queue
		DS:SI -> DWORD pointer to start of device's request queue
		Return: ZF clear if pending request
			    ES:BX -> request header
			ZF set if no more requests
	    03h "PullParticular" remove specific request from queue
		DS:SI -> DWORD pointer to start of device's request queue
		ES:BX -> request header
		Return: ZF set if request header not found
	    04h "PushRequest" push the request onto the queue
		DS:SI -> DWORD pointer to start of device's request queue
		ES:BX -> request header
		interrupts disabled
	    05h "ConsInputFilter" keyboard input check
		AX = character (high byte 00h if PC ASCII character)
		Return: ZF set if character should be discarded
			ZF clear if character should be handled normally
		Note:	called by keyboard interrupt handler so DOS can scan
			  for special input characters
	    06h "SortRequest" push request in sorted order by starting sector
		DS:SI -> DWORD pointer to start of device's request queue
		ES:BX -> request header
		interrupts disabled
	    07h "SigEvent" send signal on keyboard event
		AH = event identifier
		Return: AL,FLAGS destroyed
	    09h "ProcBlock" block on event
		AX:BX = event identifier (typically a pointer)
		CX = timeout in ms or 0000h for never
		DH = interruptable flag (nonzero if pause may be interrupted)
		interrupts disabled
		Return: after corresponding ProcRun call
			CF clear if event wakeup, set if unusual wakeup
			ZF set if timeout wakeup, clear if interrupted
			AL = wakeup code, nonzero if unusual wakeup
			interrupts enabled
			BX,CX,DX destroyed
		Note:	block process and schedules another to run
	    0Ah "ProcRun" unblock process
		AX:BX = event identifier (typically a pointer)
		Return: AX = number of processes awakened
			ZF set if no processes awakened
			BX,CX,DX destroyed
	    0Bh "QueueInit" initialize/clear character queue
		DS:BX -> character queue structure (see #02600)
		Note:	the queue size field must be set before calling
	    0Dh "QueueWrite" put a character in the queue
		DS:BX -> character queue (see #02600)
		AL = character to append to end of queue
		Return: ZF set if queue is full
			ZF clear if character stored
	    0Eh "QueueRead" get a character from the queue
		DS:BX -> character queue (see #02600)
		Return: ZF set if queue is empty
			ZF clear if characters in queue
			    AL = first character in queue
	    10h "GetDOSVar" return pointer to DOS variable
		AL = index of variable
		    03h current process ID
		BX = index into variable if AL specifies an array
		CX = expected length of variable
		Return: CF clear if successful
			    DX:AX -> variable
			CF set on error
			    AX,DX destroyed
			BX,CX destroyed
		Note:	the variables may not be modified
	    14h "Yield" yield CPU if higher-priority task ready to run
		Return: FLAGS destroyed
	    1Bh "CritEnter" begin system critical section
		DS:BX -> semaphore (6 BYTEs, initialized to zero)
		Return: AX,BX,CX,DX destroyed
	    1Ch "CritLeave" end system critical section
		DS:BX -> semaphore (6 BYTEs, initialized to zero)
		Return: AX,BX,CX,DX destroyed
		Note:	must be called in the context of the process which
			  called CritEnter on the semaphore
Note:	the DWORD pointing at the request queue must be allocated by the driver
	  and initialized to 0000h:0000h.  It always points at the next request
	  to be executed