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
112
Section 6: DRAM
Document
1250_1125-UM100CB-R
E
XAMPLE
C
HANNEL
AND
C
HIP
S
ELECT
C
ONFIGURATIONS
Configuring the memory map for channels and chip selects is usually straightforward, but there are a few
special cases. In this section some example configurations are presented. The values that are set for chip
select start and end addresses are shown in the figures, these represent bits [39:24] of the address.
The simplest memory system uses a single chip select on a single channel. Using 256Mb memory technology
a memory system could be built using 4 16Mx16 memory chips (5 if ECC is required) to give a total of 128MB
of memory.
shows how this could be configured. The standard mapping from physical to memory addressing is
used, although only the First SDRAM region is needed for 128MB from physical address
00_0000_0000
to
00_07FF_FFFF
. This maps to the same address in memory space. The controller chip selects are all disabled
apart from channel 0 chip select 0 which is set with start and end to cover this range. Any reads to the space
that is not configured will result in a bus error or UNPREDICTABLE data being returned depending on the
setting of the berr_disable bit in the
mc_config
register.
Figure 16: Example Single Channel 128MB
Using the 512Mb memory technology and using 8 (or 9 with ECC) 64Mx8 allows each chip select to have
512MB of memory. Two physical banks will therefore allow a 1GB memory system to be built. There are three
interesting configurations (two on the BCM1125/H). In these advantage is taken of the memory address space
collapsing the configuration range into a contiguous space. In the physical address space the CPU and DMA
engines use the 1GB is split up into four 256MB chunks, but in the actual memory there are just two 512MB
physical banks. The translation into memory address space pulls the four physical address regions into a
single 1GB chunk. In the simplest configuration this can be split in two and allocated to chip selects.
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
This range cannot
be accessed
bank3_map
direct map
cs0_start=00_00 cs0_end=00_08