Revision 1.02 – April 12, 2007
S5920 – PCI Product: PCI Configuration Registers
Data Book
Determining Base Address Size
BASE ADDRESS REGISTER (BADR)
The address space defined by a given base address
register is determined by writing all 1s to a given base
address register from the PCI bus and then reading
that register back. The number of 0s returned starting
from D4 for memory space and D2 for I/O space
toward the high-order bits reveals the amount of
address space desired. Tables 17 and 18 list the pos-
sible returned values and their corresponding size for
both memory and I/O, respectively.
Base Address
Register Name:
Address Offset:
10h, 14h, 18h, 1Ch, 20h
FFFFFF81h for offset 10h;
00000000h for all others
Power-up value:
Boot-load:
External nvRAM offset 050h, 54h,
58h, 5Ch, 60h (BADR0-4)
high bits Read/Write; low bits Read
Only
Included in the tables are the nvRAM/EPROM boot
values which correspond to a given assigned size. A
register returning all 0s indicates the region is
disabled.
Attribute:
Size:
32 bits
Assigning the Base Address
Base address registers are used by the system BIOS
to determine how much memory or I/O address space
a region requires in host space. The actual memory or
I/O location(s) of the space is determined by interro-
gating these registers after BIOS power-up
initialization. Bit zero of each field is used to select
whether the space required is to be decoded as mem-
ory (bit 0 = 0) or I/O (bit 0 = 1). Since this PCI device
has internal operating registers, the Base Address
Register at offset 10h is assigned to them. The
remaining four base address registers can only be
used by boot-loading them from the external nvRAM
interface.
After a base address has been sized, the BIOS can
physically locate it in memory (or I/O) space. The base
address value must be on a natural binary boundary
for the required size. For example, the first base
address register returns FFFFFF81h indicating an I/O
space (D0=1) of size 80h. This means that the 5920’s
internal registers can be selected for I/O addresses
between 00000300h through 0000037Fh, in this
example. (example 300h, 380h etc.; 338h, 340h would
not be allowable).
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