embOS software timer

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  • embOS software timer

    Hi,

    with embOS on stm32f103

    when I create a timer with a period of 1ms

    ex:

    C Source Code

    1. void TimerCallback(void)
    2. {
    3. /* Reset PA0 */
    4. GPIOA->BRR = 0x00000001;
    5. }
    7. void StartTimer()
    8. {
    9. /* Set PA0*/
    10. GPIOA->BSRR = 0x00000001;
    11. OS_CreateTimer(&Timer, TimerCallback, 1);
    12. OS_StartTimer(&Timer);
    13. }
    Display All

    what is the possible period between StartTimer() and TimerCallback().
    Does it depend on the delay between OS Tick and call to StartTimer?

    Currently I am experiencing random periods between 0 and 1ms.

  • Hello,

    the embOS software timer timing is based on the system tick.
    The system tick is generated by a hardware timer which increments the system tick per default every 1 msec (you can also work with other system ticks, e.g. 100 usec or 10 msec).
    This means that the following could happen:
    You call StartTimer() 50 usec before the next hardware timer interrupt occurs.
    In this case the time between StartTimer() and the callback function is not 1 msec but around 50 usec.
    Please have a look in the generic embOS documentation in chapter "Chapter 17 Time measurement" for more details.

    Best regards,
    Til
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