xtimer_usleep stuck randomly

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#1

Hello,

I’m facing an issue with xtimer_usleep function. All is working fine for a while but ramdomly, this function never returns, and my task stays blocked. Actually, this is because the callback that is supposed to unlock the mutex is never called. I have investigated and i saw that in xcore_timer.c:464, the second argument of the while is always false. I don’t think this is the same issue as #7347. I tried to modified XTIMER_BACKOFF but without any success. Here is my clock configuration :

`#define CLOCK_HSI (16000000U) /* internal oscillator / #define CLOCK_CORECLOCK (16000000U) / desired core clock frequency */

/* configuration of PLL prescaler and multiply values */ /* CORECLOCK := HSI / CLOCK_PLL_DIV * CLOCK_PLL_MUL / #define CLOCK_PLL_DIV RCC_CFGR_PLLDIV4 #define CLOCK_PLL_MUL RCC_CFGR_PLLMUL4 _/ configuration of peripheral bus clock prescalers /_ #define CLOCK_AHB_DIV RCC_CFGR_HPRE_DIV8 / AHB clock -> 2MHz / #define CLOCK_APB2_DIV RCC_CFGR_PPRE2_DIV1 / APB2 clock -> 2MHz / #define CLOCK_APB1_DIV RCC_CFGR_PPRE1_DIV1 / APB1 clock -> 2MHz / _/ configuration of flash access cycles */_ #define CLOCK_FLASH_LATENCY FLASH_ACR_LATENCY

/* bus clocks for simplified peripheral initialization, UPDATE MANUALLY! */ #define CLOCK_AHB (CLOCK_CORECLOCK / 8) #define CLOCK_APB2 (CLOCK_CORECLOCK / 8) #define CLOCK_APB1 (CLOCK_CORECLOCK / 8)

#define ENABLE_LSI (1)

/** * @name Timer configuration * @{ */ static const timer_conf_t timer_config[] = { { .dev = TIM2, .max = 0x0000ffff, .rcc_mask = RCC_APB1ENR_TIM2EN, .bus = APB1, .irqn = TIM2_IRQn } };

#define TIMER_0_ISR isr_tim2 #define TIMER_NUMOF (sizeof(timer_config) / sizeof(timer_config[0]))`

I have reduced all clocks to save power. I’m working on a stm32l073.

If you have any ideas about this issue, feel free to share your thoughts :slight_smile:

Thank you in advance,

Aurélien

#2

Hello Aurélien, Is it failing for any arguments to xtimer_usleep, or is it only for small values? I don't have much experience with the STM32 platforms, so someone else may have better insight into this, but this is the best idea that I can think of: When you reduce the core frequency you may have to adjust the xtimer settings for XTIMER_BACKOFF, XTIMER_ISR_BACKOFF, and XTIMER_OVERHEAD. I don't have any suggestions for any specific values, but you could start by doubling the backoffs and see if the problem goes away. Using a too large backoff constant wastes CPU cycles by actively spinning for the timeout instead of letting the timer run in the background, but these are very short time periods we are discussing here (tens of microseconds).

Hope this helps

Best regards, Joakim

#3

Hi,

Thank you very much for the reply. It was failing for any arguments to xtimer_usleep (with 1000 for example). I thought i had already played with XTIMER_BACKOFF, XTIMER_ISR_BACKOFF and XTIMER_OVERHEAD but not enough apparently. Indeed, i have set all the three settings to 100 and my device succeeded to run several days without interruption. I will try to investigate deeper to know which minimal value could be used. Thank you again :slight_smile:

Best regards,

Aurélien