CS5920 datasheet(53/160 Pages) AMCC

53 / 160 page

S5920 – PCI Product

Revision 1.01 – November 28, 2005

AMCC Confidential and Proprietary

DS1596

Data Book

BASE ADDRESS REGISTER (BADR)

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-

ga tin g th ese re gister s af ter BIOS po we r-u p

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

remaining four base address registers can only be

used by boot-loading them from the external nvRAM

interface.

Determining Base Address Size

The address space defined by a given base address

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.

Included in the tables are the nvRAM/EPROM boot

values which correspond to a given assigned size. A

disabled.

Assigning the Base Address

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).

Base Address

Address Offset:

10h, 14h, 18h, 1Ch, 20h

Power-up value:

FFFFFF81h for offset 10h;

00000000h for all others

Boot-load:

External nvRAM offset 050h, 54h,

58h, 5Ch, 60h (BADR0-4)

Attribute:

high bits Read/Write; low bits Read

Only

Size:

32 bits

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