I'm using FreeRTOS since 7.4.0 and since then I have to add to every update the initialization of the systick register on "port.c" file from the "/Source/portable/GCC/ARMCM0/" folder.
The problem is that the code initialize the portNVICSYSTICKLOAD with the calculated clock value, but after that line not initializes the portNVICSYSTICK_VAL to 0. It causes a start-up random delay of the first tick, because the we have to wait the transition from 1->0 from a counter that have a random number.
Remember that the value of this register after a reset is: Unknown.
On a speedy hardware's this is not important but in battery designs with low frequency clocks this matter.
The patch is very simple, on "/Source/portable/GCC/ARM_CM0/port.c" add:
Add the definition of the register:
>#define portNVICSYSTICKCTRL ( ( volatile uint32t *) 0xe000e010 )
>#define portNVICSYSTICKLOAD ( ( volatile uint32t *) 0xe000e014 )
>#define portNVICSYSTICKVAL ( ( volatile uint32t *) 0xe000e018 ) // <-- new line
>#define portNVICINTCTRL ( ( volatile uint32t *) 0xe000ed04 )
>#define portNVICSYSPRI2 ( ( volatile uint32t *) 0xe000ed20 )
Add the initialization of the register to zero:
>/* Configure SysTick to interrupt at the requested rate. */
>*(portNVICSYSTICKLOAD) = ( configCPUCLOCKHZ / configTICKRATEHZ ) - 1UL;
>*(portNVICSYSTICKVAL) = 0; // <-- new line
>*(portNVICSYSTICKCTRL) = portNVICSYSTICKCLK | portNVICSYSTICKINT | portNVICSYSTICKENABLE;
Thanks for the info, we will investigate this asap.