User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 6: DRAM Page
109
M
EMORY
C
ONFIGURATIONS
Before the first SDRAM access starts, the memory configuration registers must be initialized, and the correct
startup sequence issued to the memory chips. This is normally done by the BootROM code. The Broadcom
CFE firmware includes memory controller initialization which uses the Serial Presence Detect (SPD) EEPROM
information to support a wide range of memory types. This code provides the best starting point for memory
initialization.
M
APPING
The physical address space is mapped to memory address space. The physical address map has four 256
Mbyte regions and one expanded 508 Gbyte region of the address space allocated to the memory controller.
The memory controller will map the four 256 Mbyte regions into a single contiguous 1 Gbyte region of memory
address space for use by the memory channels. Memory address space is only used in the configuration of
the memory controller.
The constraints on the physical memory map of the part (see
Section: “Memory Map” on page 34
) caused the
main memory address ranges in the low 4GB of the address space to be allocated in non-contiguous blocks.
However, the memory controller configurations are more flexible if it sees them as a single contiguous block.
For example, consider a system where the actual memory consists of one single physical bank (i.e. only one
chip select) 512 MB DIMM. Since there is only one chip select this must be configured to have a single address
range. But the physical address map has one 256 MB memory block starting at zero (which contains the CPU
exception vectors and must be present) and the next 256 MB block starts at
00_8000_0000
. If the memory
controller used physical addresses there would not be a way to configure the address range to use the whole
DIMM. However, in memory address space the two memory blocks can be made contiguous and the DIMM
can be configured.
The mapping for the four physical address ranges that have zero for the upper eight bits is configured in the
channel configuration register. They can be mapped into the first four 256 MB blocks of the memory address
space. The default mapping is shown in
. There is normally no need to change from the
defaults.
C
HANNEL
S
ELECT
On the BCM1250 the two channels may be interleaved or they may be independent. If they are interleaved
then they must match in all parameters. When they are interleaved a single address bit is used to select
between them. When the channels are independent the start and end address set for the chip select
generation will also select between the two channels.
Table 60: Mapping Physical Address To Memory Controller Address
Physical Address Space
(used to access the memory)
Memory Address Space
(used to configure the controller)
Size
00_0000_0000 - 00_0FFF_FFFF
00_0000_0000 - 00_0FFF_FFFF
256 MB
00_8000_0000 - 00_8FFF_FFFF
00_1000_0000 - 00_1FFF_FFFF
256 MB
00_9000_0000 - 00_9FFF_FFFF
00_2000_0000 - 00_2FFF_FFFF
256 MB
00_C000_0000 - 00_CFFF_FFFF
00_3000_0000 - 00_3FFF_FFFF
256 MB
01_0000_0000 - 7F_FFFF_FFFF
01_0000_0000 - 7F_FFFF_FFFF
508 GB
Содержание BCM1125
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