During the development of an embedded device, I encountered a one time bug with no interruptions working. It’s important to understand that this device usually works fine, and has been for a few years now, without changes of this code part.
After a few investigation, GDB showed me that I was blocked in a while loop, of a delay function :

void delay_ns(uint32_t ns)
{
    SysTick->CTRL = 0;
    SysTick->VAL = 0;

    SysTick->LOAD = 16 * ns; // 16 for 16 MHz
    SysTick->CTRL = SysTick_CTRL_CLKSOURCE_Msk | SysTick_CTRL_ENABLE_Msk;

    while (!(SysTick->CTRL & SysTick_CTRL_COUNTFLAG_Msk)) //BUG HERE
        ;
    SysTick->CTRL = 0;
}

I’m not an MCU dev, and I’m doing my best to understand what’s at stake here, but the main informations are :

• I’m working with a Cortex-M0+
• Here’s the definition of Systick
  #define SysTick ((SysTick_Type *) SysTick_BASE ) /*!< SysTick configuration struct */
• Here’s SysTick’s Type definition

typedef struct
{
  __IOM uint32_t CTRL;               /*!< Offset: 0x000 (R/W)  SysTick Control and Status Register */
  __IOM uint32_t LOAD;               /*!< Offset: 0x004 (R/W)  SysTick Reload Value Register */
  __IOM uint32_t VAL;                /*!< Offset: 0x008 (R/W)  SysTick Current Value Register */
  __IM  uint32_t CALIB;              /*!< Offset: 0x00C (R/ )  SysTick Calibration Register */
} SysTick_Type;

I seem to understand that a error on SysTick is pretty much impossible, and as I do not fully understand MCU’s behaviour, I’m wondering where this error comes from.

I’d be glad if you were able to help me in any way !