Handling Timer Interrupt requested by multiple threads. + HELP

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#1

Hi,

I was working on RIOT porting to Stellaris Board and had some queries related to timer peripheral.

  1. How does RIOT handles timer interrupt generated by multiple threads ? For example, UART and ADC ask for timeout interrupt and are running at different threads. In case we have only 1 hwtimers, these different threads will modify each other timeout values.

  2. How much hard bounded is it for the timers to be implemented as count up timer. I see, hwtimer_spin test giving issue because of this as expected. Will it affect critical areas/functions as well.

I am facing some issues because of this, and if someone has worked it out before please help me. LM4F120H5QR microcontroller (based on Cortex M4) have default count down timer. Now, the limitation is as follows (copied from data sheet):

Note that when counting down in one-shot or periodic modes, the prescaler acts as a true prescaler and contains the least-significant bits of the count. When counting up in one-shot or periodic modes, the prescaler acts as a timer extension and holds the most-significant bits of the count.

Thus I am not able to implement Prescaler as such for the hwtimer. Has any one worked around it before ?

Thanks and Regards,

Rakendra Thapa

Mobile (+91)7760038308

#2

Hi,

1) How does RIOT handles timer interrupt generated by multiple threads ?

Use one of the abstractions, currently vtimer, soon hopefully wtimer.

2) How much hard bounded is it for the timers to be implemented as count up timer.

Up- or down-counting doesn't really make a difference for the implementation. If a timer only supports down-counting, I usually tweak timer_read to return "TIMER_MAXVALUE-timer_value". Similar for timer_set_*.

Kaspar

#3

Thanks :slight_smile: