Hello,
I've downloaded your project, tested it on nucleo-L552ZE-Q and was able to figure out the root cause of the problem.
The execution gets stuck after the first wake-up from STOP in HAL_RCC_OscConfig() called from SystemClock_Config_fromSTOP().
The while loop waiting for RCC_CR_PLLRDY ends with a timeout, since this flag is never set.
The execution then goes to Error_Handler().
A reason for that is a wrong PLL parameter passed in RCC_OscInitStruct, in particular RCC_OscInitStruct->PLL->PLLM is 1 in your case.
The correct value for the given configuration is 4.
The RCC_OscInitStruct values are obtained by calling the function HAL_RCC_GetOscConfig(), which is a previous step in SystemClock_Config_fromSTOP().
STM32 can wake-up from STOP mode with either MSI or HSI clock source. If a different clock settings is then used by the application (e.g. external clock source or PLL is used), the clock tree has to be re-configured after wake-up (that's why SystemClock_Config_fromSTOP() is called) .
In your project the internal HSI RC 16 MHz oscillator is used as wake-up source, see main():
/* Specify HSI as the clock source used after wake up from stop mode */
__HAL_RCC_WAKEUPSTOP_CLK_CONFIG(RCC_STOP_WAKEUPCLOCK_HSI);
In the SystemClock_Config_fromSTOP() the PLL is turned on and the HSI is configured as PLL source.
However, when I check your SystemClock_Config() which is used for initial clock configuration (called at the beginning of main()),
a different internal oscillator is used, namely MSI. It is used as PLL source and all the PLL parameters are set accordingly.
When you then obtain the RCC_OscInitStruct values by calling the function HAL_RCC_GetOscConfig() in SystemClock_Config_fromSTOP(),
you get the values for MSI and not for HSI (so wrong PLL configuration values)!
These are then passed to HAL_RCC_OscConfig(&RCC_OscInitStruct).
This configuration (PLLSource = HSI, PLLM = 1, PLLN = 55, PLLR = 2) results in a frequency 440 MHz generated by the PLL, which is way higher than the CPU max. frequency 110 MHz.
With the correct configuration (PLLSource = HSI, PLLM = 4, PLLN = 55, PLLR = 2), the resulting frequency is 110 MHz (so CPU max.).
There are a few ways how to solve the problem, e.g.:
1) Add the following line in the SystemClock_Config_fromSTOP() just before the HAL_RCC_OscConfig(&RCC_OscInitStruct) call:
RCC_OscInitStruct.PLL.PLLM = 4;
2) Re-write the SystemClock_Config() function to use HSI instead of MSI and set the above parameters PLLSource = HSI, PLLM = 4, PLLN = 55, PLLR = 2 (preferable solution).
Of course, this is for the max. CPU frequency 110 MHz, if you want to use lower frequency, you can adjust the values.
I also recommend to add the two followin lines at the beginning of main():
DBGMCU->CR &= ~DBGMCU_CR_DBG_STOP;
DBGMCU->CR &= ~DBGMCU_CR_DBG_STANDBY;
This will disable debug in STOP and STANDBY modes. Some IDEs enable this feature automatically, afterwards the device will wake-up from STOP mode due to an SysTick interrupt (provided that SysTick is activated and its interrupt enabled). A power cycle might be needed to apply this configuration.
You can check these values during debug in DBGMCU->CR. But this is a different story.
I will upload the modified project.
Best regards
Jaroslav Becka
