Power and clock management
RM0082
818/844
Doc ID 018672 Rev 1
37.2.1 SLEEP
In SLEEP state clock is not provided to CPU. This state maximize power saving.
System Controller clock is driven by the last selected source in DOZE mode, it could be
RTC or MAIN oscillator.
On interrupt request, normal (IRQ) or fast (FIQ), CPU wake-up and go in DOZE. Few clock
cycles (less than five) are required for this transition.
It is recommended, that to reduce power consumption, switch off all clocks to modules
which are not used for wake-up purpose (see
Section 37.6: Statiscally frequency selection
).
Interrupts enabling wake-up from SLEEP state are:
●
Ethernet MAC. In this case it is possible to disable clock to Ethernet MAC
(PERIP1_CLK_ENB.gmac_clkenb) using external clock provided by PHY MAC.
●
USB device. In this case clock to USB device cannot be switched off
(PERIP1_CLK_ENB.usbdev_clkenb) and AHB since the resume interrupt is registered
by HCLK.
●
RTC. All clocks to internal modules can be switched off (except for RTC).
●
GPIO. All clocks to internal modules can be switched off (except for GPIO).
●
TIMER. All timers, if timer clock is not switched off (see
for timer clock sources)
Note:
Sleep state is only activated if SCCTRL Mode Ctrl is set to zero and processor is in Wait-for-
Interrupt state.
Table 737.
Power state for asynchronous DRAM system (DRAM clocked by PLL2)
State
ARM
ARM clock
DRAM
Possible code
execution memory
SLEEP
Hibernate
Hibernate
off
off
Self refresh
Active
None
None
DOZE
Running
RTC Osc.
Self refresh
Internal memory
Running
RTC Osc
Active
Internal memory and
external DRAM
Running
MAIN Osc. (PLL off)
Self refresh
Internal memory
Running
MAIN Osc.(PLL off)
Active
Internal memory and
external DRAM
SLOW
Running
MAIN Osc. (PLL off)
Self refresh
Internal memory
MAIN Osc.(PLL off)
Active
Internal memory and
external DRAM
NORMAL
Running
PLL1 (Up to 333 MHz)
Active
Internal memory and
exernal DRAM