Intel
®
81341 and 81342 I/O Processors
December 2007
Developer’s Manual
Order Number: 315037-002US
581
DDR SDRAM Memory Controller—Intel
®
81341 and 81342
To support 4 GBytes of SDRAM memory, the entire memory has to be mapped in an
aligned 4-GByte address space of the 64-GByte address space. Note that some of the
64-GByte of the address space are reserved. Since the lowest 4-GByte (36-bit internal
address bits [35:32] = 0H) of the address space also contains other peripheral devices,
the 4-GByte SDRAM memory must be mapped in one of the upper 4-GByte of the
address space in order to be able to utilize the entire 4-GByte memory.
However, the Intel XScale® microarchitecture Operating System (OS) must have
access to some SDRAM memory space in the lowest 4-GByte of the address space. This
is because after reset the Intel XScale® microarchitecture only accesses the lowest
4-GByte of the address space. To support the Intel XScale® microarchitecture
requirements, two sets of base address/size fields are provided by the DMCU to allow
forming two separate memory windows.
• A Primary Memory Window is setup to map the entire 4-GByte of SDRAM memory
in an open upper 4-GByte of the address space.
• A Secondary Memory Window is setup to map part of the SDRAM memory in the
lowest 4-GByte of the address space.
Note that the secondary memory window may be smaller than the primary memory
window, and that the secondary memory window must never be larger than the total
SDRAM size defined by the SBSR, or 2 GByte, whichever is smaller. With the secondary
memory window, the Intel XScale® microarchitecture runs an Operating System (OS)
to access part of the SDRAM memory along with other peripheral devices all residing in
the lowest 4-GByte of the address space.
The primary memory window is used to access the entire 4-GByte of the SDRAM
memory by other internal bus masters like the Address Translation Units and the DMA
Engines.
Note:
The same SDRAM memory space allocated and used via the Secondary Window by the
Operating System must not be used by other internal bus masters via the Primary
Memory Window.
The primary memory window is setup using the base address registers:
“SDRAM Base Register — SDBR” on page 632
and
the size field (bits [31:27]) and the number of bank
field (bit[2]) of
Table 380, “SDRAM Bank Size Register — SBSR” on page 635
.
Warning:
Setting up a Secondary Memory Window is optional when the amount of SDRAM
memory supported is mapped in the lowest 4-GByte of the address space along with
the peripheral devices. In this case, only the Primary Memory Window is setup, and the
Secondary Memory Window is disabled (SBSR[21:16] = 0H). By default both memory
windows are disabled.