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NXP Semiconductors
PNX15xx/952x Series
Volume 1 of 1
Chapter 9: DDR Controller
PNX15XX_PNX952X_SER_N_4
NXP B.V. 2007. All rights reserved.
Product data sheet
Rev. 4.0 — 03 December 2007
9-314
2.1 Start and Warm Start
There are two different start modes for the DDR SDRAM Controller: start, and the
warm start. MMIO register IP_2031_CTL provides the interface to start the DDR
controller.
2.1.1
The Start Mode
The START eld of MMIO register IP_2031_CTL is used to trigger the start mode of
the DDR SDRAM Controller. This mode is the common start mode. It is used when
neither the DDR controller nor the DDR devices are yet initialized. This is the normal
condition after a system reset has occurred. The MMIO registers that determine the
timing and characteristics of the DDR memories should be programmed prior to the
start action is triggered, since these register values may be used to congure the
external DDR memories. The normal sequence of actions to start the DDR controller
is to program the MMIO registers that congure the different parameters of the DDR
memory devices and then set the START eld of MMIO register IP_2031_CTL to ‘1’.
This mode is used by the boot scripts.
Sequence of Actions During the Start Mode
During start (not warm start), the DDR SDRAM Controller performs the following
sequence of actions:
Apply a NOP command
Precharge all command
Load extended mode register
Load mode register, with DLL reset
256 cycles delay for DDL.
Precharge all command
Auto refresh command
Load mode register, with DLL reset deactivated
256 cycles delay
2.1.2
Warm Start
The Warm start mode is a special mode where the DDR controller initializes itself but
does not initialize the DDR devices. This mode is used in applications where the
power of the PNX15xx/952x Series is shutdown after the DDR devices have been
sent to self-refresh mode. In that state the DDR devices remained powered and
therefore they retain the data and the conguration. Once the PNX15xx/952x Series
power supplies are back on and an external reset is applied, the DDR controller can
be started by asserting the WARM_START eld of MMIO register IP_2031_CTL. By
doing so the DDR controller congures itself without conguring the DDR devices.