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Intel® PXA255 Processor Developer’s Manual 6-15
Memory Controller
This is a read/write register. Ignore reads from reserved bits. Write zeros to reserved bits.
Table 6-5. MDREFR Bit Definitions (Sheet 1 of 3)
0x4800_0004 MDREFR Memory Controller
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
reserved
K2FREE
K1FREE
K0FREE
SLFRSH
reserved
APD
K2DB2
K2RUN
K1DB2
K1RUN
E1PIN
K0DB2
K0RUN
E0PIN
DRI
Reset
0 0 0 0 0 0 1 1 1 1 0 0 1 0 1 0 0 1 * * 1 1 1 1 1 1 1 1 1 1 1 1
Bits Name Description
31:26 — reserved
25 K2FREE
SDRAM Free-Running Control
0 – SDCLK2 is not free-running
1 – SDCLK2 is free-running (ignores MDREFR[APD] or MDREFR[K2RUN] bits)
Provides synchronous memory with SDCLK2 following a reset in order to reset internal
circuitry.
24 K1FREE
SDRAM Free-Running Control
0 – SDCLK1 is not free-running
1 – SDCLK1 is free-running (ignores MDREFR[APD] or MDREFR[K1RUN] bits)
Provides synchronous memory with SDCLK1 following a reset to reset internal circuitry.
23 K0FREE
SDRAM Free-Running Control
0 – SDCLK0 is not free-running
1 – SDCLK0 is free-running (ignores MDREFR[APD] or MDREFR[K0RUN] bits)
Provides synchronous memory with SDCLK0 following a reset to reset internal circuitry.
22 SLFRSH
SDRAM Self-Refresh Control/Status
Control/status bit for entering and exiting SDRAM self-refresh and is automatically set on a
hardware or sleep reset.
0 – Self refresh disabled
1 – Self refresh enabled
SLFRSH can be set by software to force a self-refresh command. E1PIN does not have to
be cleared. The appropriate clock run bits (K1RUN and/or K2RUN) must remain set until
SDRAM has entered self-refresh and must be set prior to exiting self-refresh (clearing
SLFRSH). This capability must be used with extreme caution because the resulting state
prohibits automatic transitions for any commands.
Clearing SLFRSH is a part of the hardware or sleep reset procedure for SDRAM.
21 — reserved
20 APD
SDRAM/Synchronous Static Memory Auto-Power-Down Enable.
If APD=1, the clock enables and clock pins are automatically deasserted when none of the
corresponding partitions are being accessed unless the KxFREE bits are set.
If no SDRAM partitions are being accessed, the SDRAM chips are put into Power-Down
mode and the clocks and clock-enable pins are turned off.
If one SDRAM partition is being used and the other is not, the clock to the partition that is
not being used are turned off.
If no Synchronous Static Memory partitions are being used, the clock and clock enable to
these partitions are turned off and the memory chips are put into Power-Down mode. See
Section 6.7.
19 K2DB2
SDRAM Clock Pin 2 (SDCLK2) Divide by 2 Control/Status
0 – SDCLK2 is same frequency as MEMCLK
1 – SDCLK2 runs at one-half the MEMCLK frequency