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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262-004US
633
Memory Controller—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
11.6.2
DDRI SDRAM Control Register 0 SDCR0
The SDRAM Control Registers (SDCR[1:0]) are responsible for programming the
operation of the DDRI SDRAM state machines. The SDCR0 specifies the DIMM type,
data bus width, and some SDRAM timing parameters required by the DDRI SDRAM
state machine as defined in
“DDRI SDRAM Initialization” on page 598
SDRAM Mode Programming” on page 602
. The remaining SDRAM timing parameters
required by the DDRI SDRAM state machine are set in SDCR1.
Note:
Each parameter field contains either an IXP45X/IXP46X network processors-required
value limit or an example value derived from a typical device datasheet.
Register Name:
DDRI SDRAM Control Register 0 - SDCR0
Hex Offset Address:
CC00 E504H
Reset Hex Value:
0x0001 0004H
Register Description:
DDRI SDRAM Control Register 0
Access: See below.
31
28 27 26
24 23 22
20 19 18 17 16 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
(Rsvd
)
(Rsvd
)
(Rsvd)
(Rsvd)
(Rsvd)
(Rsvd)
(Rsvd
)
(Rsvd
)
Register
DDRI SDRAM Control Register 0 - SDCR0 (Sheet 1 of 2)
Bits
Name
Description
Default
Access
31:2
8
RAS
RAS: Active to Precharge duration in MCLK periods. This value is
computed by using the t
RAS
measured for the device (provided in the
JEDEC/Vendor specification) using the following equation:
Equation 3. RAS = t
RAS
- 1
NOTE: t
RAS
must be converted to mclks for this equation.
For example, a device specification yields that t
RAS
is 40ns (and the
device speed is 133MHz, so the mclk period is 7.5ns).
t
RAS
= (40ns / 7.5ns) = 5.33, round up to 6 mclks.
Thus, RAS = 6-1 = 5, so a value of 0101
2
should be programmed.
0H
RW
27
(Reserved)
0
2
RO
26:2
4
RP
RP: Precharge Command Period in MCLK periods. This value is
computed by using the t
RP
measured for the device (provided in the
JEDEC/Vendor specification) using the following equation:
Equation 4. RP = t
RP
- 1
NOTE: t
RP
must be converted to mclks for this equation.
For example, a device specification yields that t
RP
is 20ns (and the
device speed is 133MHz, so the mclk period is 7.5ns).
t
RP
= (20ns / 7.5ns) = 2.67, round up to 3 mclks.
Thus, RP = 3-1 = 2, so a value of 010
2
should be programmed.
000
2
RW
23
(Reserved)
0
2
RO