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SDRAM Controller (SDRC) Subsystem
•
CAS latencies of 1, 2, 3, 4, and 5 are supported (CASL).
•
Only serial mode (not interleaved mode) is supported (SIL = 0x0).
•
A burst length of 2 is supported for SDR SDRAM (BL = 0x2).
•
A burst length of 4 is supported for DDR SDRAM (BL = 0x4).
•
Burst lengths of 1 (BL = 0x0), 8 (BL =0x3), and full page (BL = 0x7) are not supported.
Writing to SDRC.
initiates an implicit Load Mode register command qualified by BA1,BA0 =
0,0 except if the NOMEMORYMRS bit is set.
10.2.5.3.5.2 Extended Mode Register 2 (EMR2)
The SDRC.
register (p = 0 or 1 for CS0 or CS1) is specific to mobile SDRAM devices. It is
a 12-bit register that controls the following standard parameters:
•
Partial Array Self-Refresh (PASR)
•
Temperature Compensated Self-Refresh (TCSR)
•
Driver Strength (DS)
The SDRC.
[2:0] PASR field programs the partial array self-refresh feature. The low power
SDR SDRAM granularity is much finer than the granularity available in a mobile DDR SDRAM. The
SDRC.
[4:3] TCSR field programs the temperature compensated self-refresh feature. The
TCSR granularity available in a low power SDR is much finer than the granularity available in a mobile
DDR.
Writing to SDRC.
initiates an implicit load mode register command qualified by BA1, BA0
= 1,0 except if
[8] NOMEMORYMRS is set.
10.2.5.3.6 Autorefresh Management
The SDRAM refresh configuration register group controls refresh management in normal operation. This
group contains two SDRC.
registers that are defined on a per-CS basis and contain
the following bit fields:
•
[1:0] ARE (where p = SDRC CS value 0 or 1)
•
[23:8] ARCV (where p = SDRC CS value 0 or 1)
These bit fields can enable and disable autorefresh. Autorefresh bursts of 1, 4, and 8 are programmed
using these fields. The autorefresh burst starts when the 16-bit autorefresh counter decrements to 0. The
ARCV field loads the autorefresh counter with a 16-bit autorefresh value. The ARCV value is calculated
using the following formula:
Refresh value = (refresh interval / clock period / number of rows) - margin
Note: Memory refresh interval in time unit. Margin is 50 (cycles).
The margin considers the possibility of an ongoing access when the counter expires, thus delaying the
effective refresh sequence.
The value to be programmed is independent of the burst-refresh configuration: if a burst-refresh is
configured, the value is automatically scaled in hardware to the burst-refresh size.
Autorefresh is enabled by programming the SDRC.
[3:0] CMDCODE field to 0x2 (where
p = 0 or 1 for SDRC CS0 or CS1).
10.2.5.3.7 Page Closure Strategy
The page closure strategy is defined on a per-bank basis by setting the SDRC.
PAGEPOLICY bit. SDRC defines one type of page closure strategy:
1. High power/high bandwidth: Bandwidth consumption is critical.
The SDRC tracks open pages. The SDRC determines whether the current access is an open page or a
closed page. The SDRC does the following:
2271
SWPU177N – December 2009 – Revised November 2010
Memory Subsystem
Copyright © 2009–2010, Texas Instruments Incorporated