Intel D15343-003 - Manual (Page 106)

Intel
®
82854 Graphics Memory Controller Hub (GMCH)
106 D15343-003
4.11.11 MMADR – Memory Mapped Range Address Register (Device #2)
This register requests allocation for the IGD registers and instruction ports. The allocation is for
512-kB and the base address is defined by bits [31:19].
4.11.12 IOBAR – I/O Base Address Register (Device #2)
This register provides the Base offset of the I/O registers within Device #2. Bits 15:3 are
programmable allowing the I/O Base to be located anywhere in 16-bit I/O Address Space. Bits 2:1
are fixed and return zero, bit 0 is hardwired to a one indicating that 8-bytes of I/O space are
decoded.
Access to the 8Bs of IO space is allowed in PM state D0 when IO Enable (PCICMD bit 0) set.
Access is disallowed in PM states D1-D3 or if IO Enable is clear or if Device #2 is turned off or if
internal graphics is disabled. Note that access to this IO BAR is independent of VGA functionality
within Device #2. Also note that this mechanism is available only through Function #0 of
Device#2 and is not duplicated in Function #1.
If accesses to this I/O bar are allowed, then the GMCH claims all 8-bit, 16-bit, or 32-bit I/O cycles
from the CPU that falls within the 8B claimed.
Address Offset:
Default Value:
Access:
Size: 14-17h
00000000h
Read/Write, Read Only
32 bits
Bit Description
31:19 Memory Base Address–R/W: Set by the OS, these bits correspond to address signals [31:19].
18:4 Address Mask–RO: Indicate 512-kB address range.
3 Prefetchable Memory–RO: Prevents prefetching.
2:1 Memory Type–RO: Indicates 32-bit address.
0 Memory / IO Space–RO: Indicates System Memory space.
Address Offset:
Default Value:
Access:
Size: 18-1Bh
00000001h
Read/Write
32 bits
Bit Description
31:16 Reserved
15:3 IO Base Address–R/W: Set by the OS, these bits correspond to address signals [15:3].
2:1 Memory Type–RO: Indicates 32-bit address.
0 Memory / IO Space–RO