MSC8144E Reference Manual, Rev. 3
12-18
Freescale
Semiconductor
DDR SDRAM Memory Controller
3.
Issues one or more auto-refresh commands to each DDR SDRAM bank (as identified by
its chip select) to refresh one row in each logical bank of the selected physical bank.
The auto refresh commands are staggered across the possible banks to reduce instantaneous
power requirements. Three sets of auto refresh commands are issued on consecutive cycles. The
initial
PRECHARGE
ALL
commands are also staggered in three groups. When the system enters self
refresh mode, only one refresh command is issued simultaneously to all physical banks. For the
entire refresh sequence, no cycle optimization occurs for the usual case where fewer banks are
installed. After the refresh sequence completes, any pending memory request is initiated after an
inactive period specified by TIMING_CFG_1[REFREC]. In addition, posted refreshes allow the
refresh interval to be set to a larger value.
Note:
The MSC8144 will initiate three cycles of Precharge ALL commands and three cycles
of Refresh commands although there are only two banks (chip select) available,
12.3.4.1 DDR SDRAM Refresh Timing
Refresh timing for the DDR SDRAM is controlled by the programmable timing parameter
TIMING_CFG_1[REFREC], which specifies the number of memory bus clock cycles from the
refresh command until a logical bank activate command is allowed. The DDR memory controller
implements bank staggering for refreshes, as shown in Figure 12-11
(TIMING_CFG_1[REFREC] = 10 in this example). System software is responsible for optimal
configuration of TIMING_CFG_1 [REFREC] at reset. Configuration must be complete before
DDR SDRAM accesses are attempted.
Figure 12-11. DDR SDRAM Bank Staggered Auto Refresh Timing
SDRAM clock
MCS0
MCAS
MRAS
MCS1
Future use; see note
MA[15–0]
ROW
CKE
REFREC
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Note: The DDR controller is designed to support up to six banks. MSC8144E uses only two banks
The third refresh command is used for devices with more than two banks.
Содержание MSC8144E
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Страница 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
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Страница 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Страница 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Страница 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Страница 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Страница 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Страница 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Страница 884: ...MSC8144E Reference Manual Rev 3 17 44 Freescale Semiconductor RapidIO Interface Dedicated DMA Controller ...
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