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PXA300 Processor and PXA310 Processor
Vol. I: System and Timer Configuration Developers Manual
Doc. No. MV-TBD-00 Rev. A
CONFIDENTIAL
Copyright © 12/13/06 Marvell
Page 164
Document Classification: Proprietary Information
December 13, 2006
Not approved by Document Control. For review only.
Note 1:In the case of a low-power mode exit with PCCE=1, software has the option of not switching
the clocks over to PLLs and continuing to run off the ring oscillator. While operating in this
mode, it is entirely legitimate for software to issue a second low-power mode-entry
command. Under this scenario, the processor is presumed to enter the second low-power
mode from D0CS mode. The implication is that upon exit from the low-power mode, the
processor is returned to D0CS mode (there is no interrupt to core and the processor continues
to run off the ring oscillator). This is true even if PCCE had been set to 0 prior to entering the
low-power mode the second time.
Note 2:PCCE affects the behavior of the clocks unit while exiting low-power mode. Therefore,
software must never update the PCCE bit while still exiting from a low-power mode. If
PCCE=1, exit from a low-power mode is signified by the PCIE interrupt. If PCCE=0, this
does not matter as the processor is out of low-power mode (by definition) when software
resumes instruction.
Note 3:When coming out of a low-power mode with PCCE = 0, software must read the
OSCC[ROS] bit to check the status of the ring oscillator and wait until the ring oscillator is
turned off before software can set PCCE = 1 for the next low-power-mode entry.
•
DMC Frequency Select (DMCFS)—Selects the frequency of the dynamic memory controller (DMEMC).
Note 1: The DMEMC gets two clocks from the clocks unit, one of which is half the frequency of the
other. The slower one is sent to the DDR memory chip, while the faster is used by the controller
itself. The frequencies controlled by this field refer to the faster clock.
Note 2: There is a complex protocol for changing the value of this field. Refer to the DMEMC chapter
for step-by-step instructions.
•
High-speed I/O bus-select (HSS)—Selects the nominal HSIO bus-clock frequency.
•
Core-system PLL clock-select (XSPCLK)—Selects the nominal system PLL-derived clock frequency used
by the core during core PLL frequency-change operations.
•
Internal memory frequency select (SFLFS)—Selects the frequency of the SRAM controller.
Note: Clock duty cycle for 208 MHz is 66/33.
•
13-MHz oscillator enable in D2 mode (13MEND2)—Disables the 13-MHz oscillator in D2 power mode.
•
D0 mode Clock Select (D0CS)—Selects the clock source to be used by the processor during D0 mode. If the
ring oscillator is selected as the D0 mode clock, some processor modules are not operational due to the clock
limitations of the ring oscillator. If the PLLs are selected as the clock source to be used by the processor, the
core uses the core PLL and all other processor modules use the system PLL.
•
SMEMC Frequency Select (SMCFS)—Selects the frequency of the static memory controller.
Note: Clock duty cycle for 208 MHz is 66/33.
•
13-MHz oscillator enable in D1 mode (13MEND1)—Disables the 13-MHz oscillator in D1 power mode.
•
System PLL Disable (SPDIS)—Turns off the system PLL clocks when not needed. If disabled, the system
PLL is not selected as the clock source and renders many peripheral units non-functional. The system PLL
can be disabled when D0CS is set to 1. Also, to avoid PLL lock-time delays, carefully select compatible
clock modes in D0 mode and D1 mode. If D0CS is set to 1, the processor uses the ring oscillator output and
executes at a reduced frequency in D0 mode. Software may disable the system and core PLLs after entering
D0CS mode to save PLL power. When the processor transitions to D1 mode, if D0CS is also set to 1, the