RM0082
Power and clock management
Doc ID 018672 Rev 1
821/844
37.5 Combining frequency scaling and clock switching
techniques
The best active power saving is obtained by combining power-management techniques
previously described; there are no limitation to do that.
37.6
Statiscally frequency selection and clock switching OFF
With this technique it is possible statically (based on performance points predefined in the
manufacturing process of a given device) define the frequency and activate only modules
requested by the application.
This technique is to apply when a constant consumption is requested by the system.
It is useful when USB ports are not requested switch of USB PLL (PLL3) and peripheral
clock could be attached to PLL1, with the right prescaler.
Also PLL2 should be OFF in synchronous mode.
37.7 PLLs
usage
The following diagram show frequency distribution in the system, with the clock domains
generated by the different PLLs.
Table 739.
Modules supporting DCS technique
Module
Module
Module
C3
GPIO
SPI
SDRAM
RTC
UART
USB 2.0 host
ADC
ARM subsystem
USB 2.0 device
Timer 2
ARM
Ethernet
Timer 3
Flash serial (SMI)
IrDA
PLL1
Internal ROM
JPEG codes
PLL2
DMA
12C
PLL3