Intel
®
81341 and 81342—DDR SDRAM Memory Controller
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
610
Order Number: 315037-002US
When the memory transaction writes less than the data bus width programmed in the
SDCR, then the DDR SDRAM Control Block translates the write transaction into a
read-modify-write transaction. For a partial write, the DDR SDRAM Control Block calculates
the ECC for the modified datum and writes it back. So, when an external unit issues a write
cycle with partial data to an DMCU port, the DMCU:
1. Issues a 64-bit (32-bit) read.
2. Modifies the value with the new portion to be written.
3. Calculates the ECC on the modified value.
4. Writes the 64-bit (32-bit) value and ECC.
Note:
When the DMCU detects a single-bit error during the read, it is corrected BEFORE being
merged with the write data so the corrected data is written back to the array. When a
multi-bit error is detected, the DMCU causes an interrupt to the core by writing to the
MCISR. The memory location is overwritten by the DMCU with the error data but valid
ECC, making the contents of memory invalid. For more details on how the DMCU
handles error conditions, see
Section 7.5, “ECC Interrupts/Error Conditions” on
.
shows an example where the data of a write is less than 64-bits wide. The
waveform illustrates how the DDR SDRAM Control Block issues a read-modify-write
cycle for the data (D
1
).
Note:
In 32-bit wide memory and in the 32-bit region in 64-bit wide memory, the DDR
SDRAM Control Block still generates 8-bit wide ECC by zero extending the data to
64-bits. A partial write is a write of less then 4-Bytes.
Figure 93. Sub 64-bit DDR SDRAM Write (D
0
)
A7856-02
CKE
CK
CK#
Command
t
CH
t
CK
t
CL
t
IS
t
IH
NOP
ACT
NOP
Read
NOP
NOP
NOP
Write
RA
BA x
COL n
NOP
NOP
t
IH
t
IS
t
IS
t
IH
A0-A9,
A11, A12
A10
t
IS
t
IH
BA0, BA1
DM
DQ
DQS
BA x
CL=2
tDQSS
RA
DIS AP
COL n
t
IS
DIS AP
t
IS
Dout
00
FF
Din
ECC Calculation Comparision,
and Correction for D0
Merge New Data and Generate
New ECC for D0
Read
Write
CAS Latency