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STM32 – Overclocking

Have you ever wondered if it was possible to overclock the STM32? It is, with a simple change in code line!
We only have to change the PLL setting, which is able to go up to 16 – so that means that we can overclock the STM32 up to 8MHz x 16 = 128 MHz
Here is the RCC Initialization code for 128MHz – remember, you also have to comment the “SYSCLK_FREQ_72MHz”, uncomment the “SYSCLK_FREQ_HSE” and set it to 128MHz in the system_stm32f10x.c

* Function Name  : RCC_Configuration
* Description    : Configures the different system clocks.
* Input          : None
* Output         : None
* Return         : None
void RCC_Configuration(void)
   /* RCC system reset(for debug purpose) */

   /* Enable HSE */

   /* Wait till HSE is ready */
   HSEStartUpStatus = RCC_WaitForHSEStartUp();

   if(HSEStartUpStatus == SUCCESS)
      /* Enable Prefetch Buffer */

      /* Flash 2 wait state */

      /* HCLK = SYSCLK */

      /* PCLK2 = HCLK */

      /* PCLK1 = HCLK/2 */

      /* PLLCLK = 8MHz * 9 = 72 MHz */
      //RCC_PLLConfig(RCC_PLLSource_HSE_Div1, RCC_PLLMul_9);
      /* PLLCLK = 8MHz * 16 = 128 MHz */
      RCC_PLLConfig(RCC_PLLSource_HSE_Div1, RCC_PLLMul_16);
      // The frequency has also been changed in system_stm32f10x

      /* Enable PLL */

      /* Wait till PLL is ready */
      while(RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET)

      /* Select PLL as system clock source */

      /* Wait till PLL is used as system clock source */
      while(RCC_GetSYSCLKSource() != 0x08)

   /* Enable peripheral clocks --------------------------------------------------*/
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOB |RCC_APB2Periph_GPIOC
         | RCC_APB2Periph_GPIOD | RCC_APB2Periph_GPIOE | RCC_APB2Periph_GPIOF | RCC_APB2Periph_GPIOG
         | RCC_APB2Periph_AFIO, ENABLE);
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  1. danw
    March 29th, 2010 at 15:08 | #1

    How do you get the USB clock to 48MHz or will this only work for non-usb applications?

    • March 29th, 2010 at 17:54 | #2

      About the USB clock I’m not sure, as I haven’t done any projects with USB yet!
      But I think if you chose to go with 128MHz, you just have to change the USB PLL to a higher value.


  2. Mox
    April 22nd, 2010 at 22:48 | #3

    How is reliability? Does it work sometimes, or will this work reliably? Will the cortex heat up (overheat)? Can the peripherals, namely the ADC work faster (maybe losing a bit or two in reliable resolution)?

    • April 23rd, 2010 at 12:27 | #4

      Dear Mox.
      I haven’t had any problems when running at 128MHz, but I don’t know about the ADC, but that would definitely also run faster, but I don’t know if any problems would occour then!
      You have to try it out – also the STM32 won’t be damaged or heat up when overclocking.

      Best Regards
      Thomas Jespersen

  3. May 30th, 2010 at 11:34 | #5

    128Mhz is just the beginnigng . About two months ago i plugged 25Mhz crystal on board for Ethernet STM32F107 family when i was changing developmnet platform from STM32F103 at 8MHz clock. PLL was set to 72Mhz when 8MHz crystal was mounted. I did’nt change PLL’s configuration for STM32F107, and guess what? It was working ! at 225 MHz with FreeRTOS onboard. Led was blinking faster, PWM was goin faster, UART to !

    • May 30th, 2010 at 11:42 | #6

      Amazing that it works, but it won’t work reliably.
      The problem is that the chip and the things inside it isn’t made for speeds that fast, so I think you would see that the chip will go into the Hard Fault routine most of the time!

  4. Medved
    May 24th, 2011 at 20:36 | #7

    And how about flash latency? Normally flash runs at maximum speed of 24MHz, therefore the processor has to wait for instructions for longer than 2 cycles. So is the flash also read faster? I can’t believe that.

  5. May 26th, 2011 at 07:32 | #8

    I don’t know if flash is running faster, as I haven’t tried reading/writing to flash when overclocked. Though I think you will experience problems when trying to access the flash!

    Best Regards
    Thomas Jespersen

  6. Radzick
    June 6th, 2011 at 21:56 | #9


    Nice piece of code. Sharing is caring 🙂

    I have tried it with STM32 Discovery running STM32F100RBT6B (Medium Density Value Line). It works OK up to 64 MHz. 72 MHz and over gives me HardFault interrupt. Maybe I am doing something wrong… But with different configurations and trying out to set up default configuration to 72 MHz (changing system_stm32f10x.c) didn’t help.

    So far I am happy. I need higher frequency to set more precise timer clock. Do you have a clue how will power demands after changing the clock (higher, lower, depends on the code)?

  7. June 29th, 2011 at 20:49 | #10

    Dear Radzick.
    Wow, I’m really amazed that you could overclock it that far.
    It doesn’t surprise me that it doesn’t work at 72MHz, which is 3 times the specified maximum clock.
    About the power consumption it is definitely going to rise when overclocking – the same happens with the heat.


  8. farhad
    January 2nd, 2014 at 21:46 | #11

    Hello guys
    I tested the STM32F103VET6 in 128MHz and it worked good without any failure.without overheating problem at 3.3v power supply.But i think USB can not work in this situation because it requires 48MHz.”If the USB interface is used in the application, the PLL must be programmed to output 48 or
    72 MHz. This is needed to provide a 48 MHz USBCLK.”

    Best Regards
    Farhad Rouzdar
    From Azerbaijan

  9. stephen cheung
    October 12th, 2014 at 17:31 | #12

    I had tried to use 8MHz crystal, PLL 16 to 128Mhz, the system, LCD, Flash read write, all works good.

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