Microcontroller stops working when I slow down the clock - Where do I even begin to debug this?

[arnold_w]

Posted on July 11, 2016 at 18:11

I am working with the STM32F405 microcntroller and in main() I have the following loop:

while
(TRUE)
{
UART_TransmitNullTerminatedString((uint8_t*)
''\r\nMicrocontroller alive ''
);
}

I run this firmware on 2 different PCB:s and it's working fine on PCB #1, but on PCB #2 it hangs after 3-4 seconds. Now, it would be easy to conclude that PCB #2is broken, but the strange thing is that PCB #2starts working fine if I run the microcontroller faster. I use the following code to switch clock frequency:

void
ClockSwitch(ClockFreqType clockFreq)
{
// The code below was taken from HAL_RCC_DeInit() in file stm32f4xx_hal_rcc_ex.c
/* Set HSION bit */
SET_BIT(RCC->CR, RCC_CR_HSION | RCC_CR_HSITRIM_4);
/* Reset CFGR register */
CLEAR_REG(RCC->CFGR);
/* Reset HSEON, CSSON, PLLON, PLLI2S */
CLEAR_BIT(RCC->CR, RCC_CR_HSEON | RCC_CR_CSSON | RCC_CR_PLLON| RCC_CR_PLLI2SON);
/* Reset PLLCFGR register */
CLEAR_REG(RCC->PLLCFGR);
SET_BIT(RCC->PLLCFGR, RCC_PLLCFGR_PLLM_4 | RCC_PLLCFGR_PLLN_6 | RCC_PLLCFGR_PLLN_7 | RCC_PLLCFGR_PLLQ_2);
/* Reset PLLI2SCFGR register */
CLEAR_REG(RCC->PLLI2SCFGR);
SET_BIT(RCC->PLLI2SCFGR, RCC_PLLI2SCFGR_PLLI2SN_6 | RCC_PLLI2SCFGR_PLLI2SN_7 | RCC_PLLI2SCFGR_PLLI2SR_1);
/* Reset HSEBYP bit */
CLEAR_BIT(RCC->CR, RCC_CR_HSEBYP);
/* Disable all interrupts */
RCC->CIR = 0x00000000;
RCC_OscInitTypeDef RCC_OscInitStruct;
RCC_ClkInitTypeDef RCC_ClkInitStruct;
// First, switch to HSI to bypass the PLL
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_7);
// The code below was generated with STM32CubeMX
switch
(clockFreq)
{
case
CLOCK_FREQ_1_MHz:
{
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.HSICalibrationValue = 16;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
HAL_RCC_OscConfig(&RCC_OscInitStruct);
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV16;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
break
;
}
case
CLOCK_FREQ_2_MHz:
{
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.HSICalibrationValue = 16;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
HAL_RCC_OscConfig(&RCC_OscInitStruct);
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV8;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
break
;
}
case
CLOCK_FREQ_4_MHz:
{
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.HSICalibrationValue = 16;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
HAL_RCC_OscConfig(&RCC_OscInitStruct);
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV4;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
break
;
}
case
CLOCK_FREQ_8_MHz:
{
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.HSICalibrationValue = 16;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
HAL_RCC_OscConfig(&RCC_OscInitStruct);
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV2;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
break
;
}
case
CLOCK_FREQ_16_MHz:
{
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.HSICalibrationValue = 16;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
HAL_RCC_OscConfig(&RCC_OscInitStruct);
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
break
;
}
case
CLOCK_FREQ_32_MHz:
{
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.HSICalibrationValue = 16;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
RCC_OscInitStruct.PLL.PLLM = 8;
RCC_OscInitStruct.PLL.PLLN = 64;
RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
RCC_OscInitStruct.PLL.PLLQ = 4;
HAL_RCC_OscConfig(&RCC_OscInitStruct);
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV2;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
break
;
}
case
CLOCK_FREQ_64_MHz:
{
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.HSICalibrationValue = 16;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
RCC_OscInitStruct.PLL.PLLM = 8;
RCC_OscInitStruct.PLL.PLLN = 64;
RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
RCC_OscInitStruct.PLL.PLLQ = 4;
HAL_RCC_OscConfig(&RCC_OscInitStruct);
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
break
;
}
case
CLOCK_FREQ_128_MHz:
{
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.HSICalibrationValue = 16;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
RCC_OscInitStruct.PLL.PLLM = 8;
RCC_OscInitStruct.PLL.PLLN = 128;
RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
RCC_OscInitStruct.PLL.PLLQ = 4;
HAL_RCC_OscConfig(&RCC_OscInitStruct);
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV4;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV2;
break
;
}
default
:
{
break
;
}
}
HAL_RCC_ClockConfig(&RCC_ClkInitStruct, getNumWaitStates(clockFreq));
SystemCoreClockUpdate();
}

At 8 MHz PCB #1 is working fine, but PCB #2 hangs after about 3-4 seconds. If I instead run at 16 MHz or faster, then both PCB:s work fine. Does anybody have any suggestions how I can tackle this problem? Are there any status registers I should pay attention to? I'm running off a power supply and power consumption doesn't seem to be an issue (it's not drawing too much current and, surprisingly, the current consumption doesn't go down after PCB #2 hangs).

[Tesla DeLorean]

Posted on July 11, 2016 at 19:49

Does anybody have any suggestions how I can tackle this problem?

Have a working Hard Fault Handler.

Output SYSCLK via MCO2 (PC9)

Output a clock from a TIM, toggling a GPIO

Output a toggling GPIO from a TIM Update Interrupt (try both highest and lowest preempt priority)

Output a toggling GPIO from other interrupts you have running.

Identify any while loops that can stick, instrument them.

Review the USART status, make sure there aren't overrun, framing errors, etc jamming it up.

The goal is to understand what is and isn't clocking, what is behaving differently and where it is stuck.

[jpeacock23]

Posted on July 11, 2016 at 23:01

If switching with PLL on do you turn it off first, before changing oscillator?

When downgrading frequency do it in stages.  Check for PLL on, and if so switch to same oscillator with PLL off, then stop PLL.  Change oscillator and then enable PLL again if it's needed.

Look at the RCC registers, they show which oscillators are on, if PLL is on and how the PLL is configured.  SYSCLK/HCLK instruction clock is the product of oscillator (HSE, HSI, MSI) and PLL multiplier.  When calculating the PLL multiply/divide factors make sure the intermediate VCO frequency stays in range.

You might want to make sure AHB and APB are adjusted for frequency too.  This isn't always a linear relationship with frequency...below certain values AHB and APB aren't divided down.

If your part has voltage scaling make sure it's in range for frequency too.

Frequency/voltage scaling on STM32s is a non-trivial exercise, especially on L1 and L4 series, but even the F4 PLL can be complicated.

  Jack Peacock