BCM1250/BCM1125/BCM1125H
User Manual
10/21/02
B r o a d c o m C o r p o r a t i o n
Page
116
Section 6: DRAM
Document
1250_1125-UM100CB-R
In
it can be seen that 3GB of the aliases are hidden in the memory address space that cannot be
accessed from the physical space. The only alias that needs to be considered is the
01_0000_0000 -
01_3FFF_FFFF
alias of
00_0000_0000 - 00_3FFF_FFFF.
A particular memory location must be
accessed through only one of these ranges or the coherency algorithm will break down. The CPU exception
vectors are all at the bottom of memory so in most systems the
00_0000_0000 - 00_3FFF_FFFF
space
will be used. Some systems may choose to use
00_0000_0000 - 00_1FFF_FFFF
(accessible through
kseg0) and
01_2000_0000 - 01_3FFF_FFFF
to keep the upper range contiguous with the second 1GB --
however this only allows DMA access to the low 256MB from the PCI (or from 32-bit addressing peripherals
bridged from the HT interface) since the DMA and CPU accesses must use the same physical range. (PCI
accesses translated by the BAR0 map could be used.)
Figure 20: Example 2GB with two chip selects interleaved on one channel
Channel 0, chip select 0
bank2_map
bank1_map
bank0_map
Expansion space
Physical Address
(used by CPU and DMA)
MC Address Space
(only used for MC configuration)
00_0000_0000
00_1000_0000
00_8000_0000
00_9000_0000
00_A000_0000
00_C000_0000
00_D000_0000
01_0000_0000
80_0000_0000
FF_FFFF_FFFF
First SDRAM
Peripherals
Second SDRAM
Third SDRAM
Reserved
Fourth SDRAM
Peripherals/L2 mgmt
SDRAM Expansion
HT
bank3_map
Alias of bank0-3
cs0_start=00_00 cs0_end=01_80
Channel 0, chip select 1
cs1_start=00_00 cs1_end=01_80
cs_interleave=bit7, cs_mode=mixed_cs
01_4000_0000
01_8000_0000
Should not be used
Address bit 32 is not mapped to SDRAMs
Alias of bank0-3
Upper 1GB
Alias of upper 1GB
Alias of upper 1GB
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