Intel
®
81341 and 81342—DDR SDRAM Memory Controller
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
606
Order Number: 315037-002US
7.3.3.11 DDR SDRAM Refresh Cycle
Since the DDR SDRAM is a dynamic memory, the DMCU issues a refresh cycle
periodically. The interval of these refresh cycles is programmable in the RFR register.
The DDR SDRAM device generates the refresh address internally. The DMCU initiates
two sequential refresh cycles (one per bank) after the DMCUs refresh timer expires and
any current transaction is complete. Once the refresh timer expires, the DMCU knows
that a refresh cycle is necessary.
— The refresh timer continues to count for the next refresh cycle.
• The DMARB allows the current transaction to complete.
— When the DDR SDRAM Control Block and the DDR SDRAM array are
transferring data, or a NIBPTQ tenure is ongoing, the refresh cycle is queued
until the transaction is complete or the NIBPTQ tenure expires.
• The DDR SDRAM Control Block closes all open pages with a
precharge-all
command
to all the populated DDR SDRAM banks.
— The DDR SDRAM Control Block resets the page register valid bits.
• The DDR SDRAM Control Block issues an
auto-refresh
command to DDR SDRAM
bank 0.
— This command affects all internal leaves.
• In the next cycle, the DDR SDRAM Control Block issues an
auto-refresh
command to
DDR SDRAM bank 1.
• After T
rfc
cycles, the DDR SDRAM Control Block can service a new transaction or
another refresh cycle.
It is recommended that the RFR (
“Frequency Register — RFR” on page 651
) is
programmed with the value to achieve 7.8
µ
s, though some DDR SDRAM devices may
provide for the ability to refresh at a period of 15.6
µ
s. The value is based on the
frequency of the DDR SDRAM and
can provides for these two typical values.
The longest possible internal bus transaction is writing a 1 Kbyte page where each data
cycle results in a read-modify-write due to partial writes (see
ECC Generation for Partial Writes” on page 609
). The longest possible NIBPTQ tenure is
16 transactions where each of the transaction are page misses and partial writes. Such
periods potentially require queueing two refresh cycles.
Table 369. Typical Refresh Frequency Register Values
DDR Speed
7.8
µ
s Value
15.6
µ
s Value
400 MHz
618H
C30H
533 MHz
820H
1040H