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2.11 Reset Considerations
DDR2
memory
controller
registers
Hard
Reset from
PLLC1
State
machine
VRST
VCTL_RST
DDR
PSC
Peripheral Architecture
Once in self-refresh mode, the DDR2 memory controller input clocks (VCLK and X2_CLK) may be gated
off or changed in frequency. Stable clocks must be present before exiting self-refresh mode. See
Section 2.16
for more information describing the proper procedure to follow when shutting down DDR2
memory controller input clocks.
The DDR2 memory controller has two reset signals, VRST and VCTL_RST. The VRST is a module-level
reset that resets both the state machine as well as the DDR2 memory controller memory-mapped
registers. The VCTL_RST resets the state machine only. If the DDR2 memory controller is reset
independently of other peripherals, the user's software should not perform memory, as well as register
accesses, while VRST or VCTL_RST are asserted. If memory or register accesses are performed while
the DDR2 memory controller is in the reset state, other masters may hang. Following the rising edge of
VRST or VCTL_RST, the DDR2 memory controller immediately begins its initialization sequence.
Command and data stored in the DDR2 memory controller FIFOs are lost.
Table 13
describes the different
methods for asserting each reset signal. The Power and Sleep Controller (PSC) acts as a master
controller for power management for all of the peripherals on the device. For detailed information on
power management procedures using the PSC, see the
TMS320C642x DSP Power and Sleep Controller
(PSC) User's Guide
(
SPRUEN8
).
Figure 15
shows the DDR2 memory controller reset diagram.
Table 13. Reset Sources
Reset Signal
Reset Source
VRST
Hardware/device reset
VCTL_RST
Power and sleep controller
Figure 15. DDR2 Memory Controller Reset Block Diagram
DDR2 Memory Controller
30
SPRUEM4A – November 2007
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