STM32f2xx could not work with maximum frequency

Question

I'm using default configuration (according to UM1061, RCC section) to configure an SMT32F215RG to work with 120MHZ CPU clock. here is my configurations:

/* PLL_VCO = (HSE_VALUE or HSI_VALUE / PLL_M) * PLL_N */
#define PLL_M 25 /* For HSE value equal to 25 MHz */
#define PLL_N 240
/* SYSCLK = PLL_VCO / PLL_P */
#define PLL_P 2
/* USB OTG FS, SDIO and RNG Clock = PLL_VCO / PLLQ */
#define PLL_Q 5
/* In this example:
PLL_VCO = 240 MHz
SYSCLK = 120 MHz
*/
/***************************************************************/
/* PLL (clocked by HSE) used as System clock(SYSCLK) source */
/***************************************************************/
__IO uint32_t StartUpCounter = 0, HSEStartUpStatus = 0;
/* Enable HSE */
RCC_HSEConfig(RCC_HSE_ON);
/* Wait till HSE is ready */
HSEStartUpStatus = RCC_WaitForHSEStartUp();
if (HSEStartUpStatus == SUCCESS)
{
/* Flash 3 wait state, prefetch buffer and cache ON */
FLASH_SetLatency(FLASH_Latency_3);
FLASH_PrefetchBufferCmd(ENABLE);
FLASH_InstructionCacheCmd(ENABLE);
FLASH_DataCacheCmd(ENABLE);
/* HCLK = SYSCLK */
RCC_HCLKConfig(RCC_SYSCLK_Div1);
/* PCLK2 = HCLK/2 */
RCC_PCLK2Config(RCC_HCLK_Div2);
/* PCLK1 = HCLK/4 */
RCC_PCLK1Config(RCC_HCLK_Div4);
/* Configure the main PLL clock to 120 MHz */
RCC_PLLConfig(RCC_PLLSource_HSE, PLL_M, PLL_N, PLL_P, PLL_Q);
/* Enable the main PLL */
RCC_PLLCmd(ENABLE);
/* Wait till the main PLL is ready */
while (RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET)
{}
/* Select the main PLL as system clock source */
RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);
/* Wait till the main PLL is used as system clock source */
while (RCC_GetSYSCLKSource() != RCC_CFGR_SWS_PLL)
{}
}
else
{ /* If HSE fails to start-up, user can add here some code
to deal with this error */
}

for testing that, I'm using a blinking LED (in pooling mode), VDD is 3.3 volts & I use a 25 MHZ quartz.
The problem is here that the program does NOT work at all or it begins to work & stops after one or two seconds.
I used a debugger to trace it & I found that a Hard Fault occures & execution enters into HardFault_Handler infinity loop of startup_stm32fxx.s
I checked the board several times & I'm sure it has no issue, also the same program works fine when I decrease cpu clock to a lower value (by changing PLL params, e.g set PLL_P=4). Seems all frequencies above 100MHZ causes some kind of problem. I guessed it may related to Flash access latency, but according to the datasheet with 3.3V of VDD it must works with 3 wait states & changing wait cycles did not helped me.

• abey: What's the value of the HFSR?

Answer 1

I forgot to put capacitors on VCAP pins & it causes the issue. Connecting a 2.2UF capacitor on one of the VCAP pins solved the problem

• iouzzr: Vcap is decouping cpacitor for mcu internal voltage, which is 1.2v, failed to connect them will result bad power delivery network.