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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—Memory Controller
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
Developer’s Manual
August 2006
602
Order Number: 306262-004US
location has a valid ECC byte. The Intel XScale processor processor must be used to fill
the memory array with a constant, thereby initializing the associated ECC bytes in the
process. If the memory array is not initialized, the BIU or PCC may attempt to read
memory locations beyond the specified word(s). In this case, the MCU will report an
ECC error even though software did not specifically request the un-initialized data.
11.2.2.9
DDRI SDRAM Mode Programming
The MCU programs the DDRI SDRAM devices through a
mode-register-set
command.
During the initialization sequence this command sets the DDRI SDRAM mode register
(see
Section 11.2.2.8, “DDRI SDRAM Initialization”
) by programming the SDIR and
SDCR[1:0].
The DDRI SDRAM state machine ensures that a
row-activate
command is issued no
sooner than T
mrd
cycles after the
mode-register-set
command.
The values to be programmed in the SDCR[1:0] registers are based on the DDRI
SDRAM devices being interfaced to the IXP45X/IXP46X network processors. Because
the parameters that define the time between allowed commands are programmable,
this allows flexibility in the type of DDRI device that is selected, in addition to de-
coupling the hardware to any frequency dependencies.
Note:
The MCU_DDRSM will NOT interact properly with the DDRI SDRAM until the SDCR[1:0]
registers have been programmed.
The duration between valid commands must be programmed by the user before the
DDRSM can interact properly with the DDRI. These parameters are defined by either
JEDEC and/or within this document in the timing diagrams and equations in
11.6.2, “DDRI SDRAM Control Register 0 SDCR0”
.
The timing parameters for all non-read and non-write commands are derived directly
from the JEDEC Standard Double Data Rate (DDR) SDRAM Specification JESD79, June
2004 and JEDEC DDR - II SDRAM Specification, September 2002. These parameters,
and their relationship to each other, are outlined in
. Please see the device
specification for the timing parameters specific to the DDR device that is to be
implemented in the system.