Revision 1.02 – April 12, 2007
S5920 – PCI Product: PCI Configuration Registers
Data Book
Figure 17. Base Address Register - Memory
0
0
Bit
31
x
30
x
29
4
3
0
2
0
1
0
Value
Base Address
Memory Space
Indicator (RO)
Type (RO)
00 = Locate
Anywhere (32)
01 = Below 1 MB
10 = Locate Anywhere (64)
11 = Reserved
Prefetchable (RO)
Programmable (RO)
D31 D30 Add-On Bus Width
0
0
1
1
0
1
0
1
Region Disable
8 bits
16 bits
32 bits
Bit
Description
31:4
Base Address Location. These bits locate the decoded region in memory space. Only bits which return a 1 after
being written as 1 are usable for this purpose. Except for Base Address Register 0, these bits are individually
enabled by the contents sourced from the external boot memory.
3
Prefetchable. When set as a 1, this bit signifies that this region of memory can be cached. Cacheable regions
can only be located within the region altered through PCI bus memory writes. This bit, when set, also implies
that all read operations will return the data associated for all bytes regardless of the Byte Enables. Memory
space which cannot support this behavior should leave this bit in the zero state. this bit is set by the reset pin
and later initialized by the external boot memory option. Base Address Register 0 always has this bit set to 0.
This bit is read only from the PCI interface. This bit has no implementation in the S5920 other than providing it
during a configuration read cycle.
2:1
Memory Type. These bits define whether the memory space is 32 or 64 bits wide and if the space location is
restricted to be within the first megabyte of memory space. The encoding is as follows:
Bits
Description
2
0
0
1
1
0
Region is 32-bits wide and can be located anywhere in 32-bit memory space.
1
0
Region is 32 bits wide and must be mapped below the first Mbytes of memory space.
Region is 64 bits wide and can be mapped anywhere within 64-bit memory space. (Not supported
by this device.)
1
1
Reserved.
2
0
Note: The 64-bit memory space is not supported by this device. Bit 2 is hardwired to 0. Options are restricted to
desired to memory space anywhere within 32-bit memory space or located in the first megabyte. For Base
Addresses 1 through 4, this bit is cleared by the reset pin and later initialized by the external boot memory
option.
Space Indicator = 0. When set to 0, this bit defines a base address region as memory space and the remaining
bits in the base address register are defined as shown in Figure 17.
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