DDR memory controller (MPMC)
RM0082
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Doc ID 018672 Rev 1
Memory Controller will only attempt to gate the clock if it is configured for mobile device
operation. For non-mobile memory devices in this low power mode, the Memory
Controller will operate identically to the Memory Power-Down mode without the clock
gating (Mode 1).
3. Memory
Self-Refresh
The Memory Controller sets the memory devices into self-refresh. In this mode, the
Memory Controller and memory clocks are fully operational and the CKE input bit to the
memory devices is de-asserted. Since the memory automatically refreshes its
contents, the Memory Controller does not need to send explicit refreshes to the
memory.
4.
Memory Self-Refresh with Memory Clock Gating
The Memory Controller sets the memory devices into self-refresh and gates off the
clock to the memory devices. Before the memory devices are removed from self-
refresh, the clock will be gated on again.
5.
Memory Self-Refresh with Memory and Controller Clock Gating
This is the most effective low power mode of the Memory Controller: The Memory
Controller sets the memory devices self-refreshing and gates off the clock toward them.
In addition, the clock toward the Memory Controller and the programming parameters
will be gated off, except to a small portion of the DLL, which must remain active to
maintain the lock. Before the memory devices are removed from self-refresh, the
Memory Controller and memory clocks will be gated on.
10.7.2
Low power mode control
The Memory Controller may enter and exit the various low power modes in the following
ways:
●
Automatic Entry:
●
When the Memory Controller is idle, 4 different timing counters begin counting the
cycles of inactivity. If any of the counters expires, the Memory Controller enters the low
power mode associated with that counter.
●
Manual Entry:
●
The user may set any low power mode by setting the bit of the lowpower_control
parameter associated with the desired mode. The Memory Controller will enter the
selected low power mode when it is has completed its current burst.
Automatic and Manual entry methods are both controlled by two parameters:
lowpower_control and lowpower_auto_enable. The lowpower_control parameter contains
individual enable/disable bits for each low power mode, and the lowpower_auto_enable
parameter controls whether each mode will be entered automatically or manually.
Automatic entry
Automatic Entry will occur as all the following conditions are matched:
●
The mode is programmed for automatic entry by setting the relevant bit in the
lowpower_auto_enable parameter to 1'b1.
●
The particular mode is enabled in the lowpower_control parameter.
●
The Memory Controller is idle.
●
The counter associated with this mode expires.