K70 MCU frequency change

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K70 MCU frequency change

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evgenik
Contributor IV

Hi.

How can I reduce Kinetis K70 MCU frequency before going to STOP mode and increase after wakeup?

Thanks.

Evgeni

2 Replies

218 Views
evgenik
Contributor IV

I am using the next configuration in System_Init() (attached 2 files):

// Initialize PLL0
// PLL0 will be the source for MCG CLKOUT so the core, system, FlexBus, and flash clocks are derived from it
mcg_clk_hz = pll_initialization(OSCINIT, // Initialize the oscillator circuit
   OSC_0, // Use CLKIN0 as the input clock
   CLK0_FREQ_HZ, // CLKIN0 frequency
   LOW_POWER, // Set the oscillator for low power mode
   CLK0_TYPE, // Crystal or canned oscillator clock input
   PLL_0, // PLL to initialize, in this case PLL0
   PLL0_PRDIV, // PLL predivider value
   PLL0_VDIV, // PLL multiplier
   MCGOUT); // Use the output from this PLL as the MCGOUT

// Check the value returned from pll_initialization() to make sure there wasn't an error
if (mcg_clk_hz < 0x100)
while(1);

// Initialize PLL1
// PLL1 will be the source for the DDR controller, but NOT the MCGOUT
pll_1_clk_khz = (pll_initialization(NO_OSCINIT, // Don't init the osc circuit, already done
   OSC_0, // Use CLKIN0 as the input clock
   CLK0_FREQ_HZ, // CLKIN0 frequency
   LOW_POWER, // Set the oscillator for low power mode
   CLK0_TYPE, // Crystal or canned oscillator clock input
   PLL_1, // PLL to initialize, in this case PLL1
   PLL1_PRDIV, // PLL predivider value
   PLL1_VDIV, // PLL multiplier
   PLL_ONLY) / 1000); // Don't use the output from this PLL as the MCGOUT

My system all time stay in STOP mode and wake up on RTC alarm. Therefore I want to reduce MCU frequency to minimal power consumption before STOP mode and on RTC Wake up restore to working frequency.

Thanks.

Evgeni

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218 Views
charlesasquith
NXP Employee
NXP Employee

Hi Evgeni,

your question is fairly vague. How you can alter your clock frequency depends on your clock configuration. If you are using the FLL or PLL you can always lower the multiplication factor it's scaling the respective reference clock by in the MCG module. You can also increase the pertinent clock divider in the SIM module to lower the frequency. Or if you want to raise the frequency, just do the opposite of the prior suggestions. :smileyhappy:

It's totally up to you how and where in your program you decide to change your clock configuration.