Format of Device Descriptor Table (DDT):
Offset	Size	Description	)
 00h	BYTE	bits 7-4: reserved (set to 0)
		bits 3-0: slot of device (0 = system board)
 01h	BYTE	bits 7-4: second interrupt for this device (0 = none)
		bits 3-0: first interrupt for this device (0 = none)
 02h	BYTE	bits 7-4: second arbitration level for this device
		bits 3-0: first arbitration level for this device
 03h	WORD	DDT indicators (see #00536)
 05h	BYTE	reserved (0)
 06h	WORD	device ID (0 = none)
 08h	WORD	starting address of first  I/O block (0 = none)
 0Ah	WORD	starting address of second I/O block (0 = none)
 OCh	WORD	starting address of third  I/O block (0 = none)
 OEh	DWORD	start of first non-system memory block (0 = none)
 12h	WORD	size of first non-system memory block (in kilobytes)
 14h	DWORD	start of second non-system memory block (0 = none)
 18h	WORD	size of second non-system memory block (in kilobytes)
 1Ah	BYTE	implementation identifier of the device
 1Bh	BYTE	implementation revision level of the device
Note:	I/O block addresses and non-system memory addresses are listed in
	  ascending order in each DDT entry.