SysTick_Handler in gd32-spl-freertos shouldn't auto clear overflow flag of SysTick

[yyjdelete]

SysTick_Handler in gd32-spl-freertos(without cmsis_os2) shouldn't auto clear overflow flag of SysTick.

gd32-pio-projects/gd32-spl-freertos/src/main.c

Lines 139 to 149 in 76bdc2d

	extern void xPortSysTickHandler(void);
	void SysTick_Handler(void)
	{
	/* Clear overflow flag */
	SysTick->CTRL;
	if (xTaskGetSchedulerState() != taskSCHEDULER_NOT_STARTED)
	{
	/* Call tick handler */
	xPortSysTickHandler();
	}
	}

It will break tickless mode for FreeRTOS(#define configUSE_TICKLESS_IDLE 1), since the default vPortSuppressTicksAndSleep will check the flag

gd32-pio-projects/gd32-spl-freertos/lib/FreeRTOS/src/portable/ARM_CM3/port.c

Lines 552 to 566 in d16b658

	/* Disable the SysTick clock without reading the
	* portNVIC_SYSTICK_CTRL_REG register to ensure the
	* portNVIC_SYSTICK_COUNT_FLAG_BIT is not cleared if it is set. Again,
	* the time the SysTick is stopped for is accounted for as best it can
	* be, but using the tickless mode will inevitably result in some tiny
	* drift of the time maintained by the kernel with respect to calendar
	* time*/
	portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT );
	/* Determine if the SysTick clock has already counted to zero and
	* been set back to the current reload value (the reload back being
	* correct for the entire expected idle time) or if the SysTick is yet
	* to count to zero (in which case an interrupt other than the SysTick
	* must have brought the system out of sleep mode). */
	if( ( portNVIC_SYSTICK_CTRL_REG & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )

[maxgerhardt]

Interesting. That comes from https://github.com/STMicroelectronics/STM32CubeF4/blob/master/Middlewares/Third_Party/FreeRTOS/Source/CMSIS_RTOS_V2/cmsis_os2.c#L150-L168.

So the code should rather be

 extern void xPortSysTickHandler(void); 
 void SysTick_Handler(void) 
 { 
     /* only clear overflag in not-tickless mode */
#if !defined(configUSE_TICKLESS_IDLE) || configUSE_TICKLESS_IDLE  == 0
     /* Clear overflow flag */ 
     SysTick->CTRL; 
#endif
     if (xTaskGetSchedulerState() != taskSCHEDULER_NOT_STARTED) 
     { 
         /* Call tick handler */ 
         xPortSysTickHandler(); 
     } 
 } 

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