Intel PCI User Manual

74

All base address registers have the following fields:

Mem

0

R

0b for 
mem
1b for I/O

0b indicates memory space. 1b indicates I/O.
 

Type

2:1

R

00b for 32-
bit
10b for 64-
bit

Indicates the address space size.
00b = 32-bit
10b = 64-bit

Prefetch

3

R

0b

0b = non-prefetchable space
1b = prefetchable space
Ethernet controller implements non-prefetchable space 
since it has read side-effects.

Address

31:0

R/W

0b

The lower bits of the address are hard-wired to 0b. The 
upper bits can be written by the system software to set 
the base address of the register or flash address space.

The memory register space is 128K bytes. The 
Memory Register BAR has:

• Bits 16:4 are hard-wired to 0b.
• Bits 63:17 or 31:17 are read/write.

The size of the flash space can very between 64 KB and 
512 KB depending on the FLASH size read from the 
EEPROM. The Memory Flash BAR has these 
characteristics:

Flash Size Valid Bits Zero Bits
(R/W)    (RO)

• 64 KB 63/31:16 15:4
• 128 KB 63/31:17 16:4
• 256 KB 63/31:18 17:4
• 512 KB 63/31:19 18:4

The size of the IO register space is 8 bytes. The I/O 
Register BAR has: 

• Bit 2 hard-wired to 0b
• Bits 31:3 as read/write