nrf51822 application timer issue

[sowmya]

Hello ,

I am initialising application timer with prescale of 327 for 10 ms interrupt delay. I created a timer slot using app_timer_create(&ulTestTimer, APP_TIMER_MODE_REPEATED, test_timeout); and started the timer app_timer_start(ulTestTimer, 1, NULL); where the callback should be called for every 10ms.

Is this correct? If yes, I am not getting the interrupt. But the same is working when I start the timer with 5 value corresponding to 50ms, as app_timer_start(ulTestTimer, 5, NULL);

Am using with S110 softdevice v 8.0 and SDK 9.0.

Regards, Sowmya

[Anders Strand]

Hey.

Check out the documention for app_timer_start. It says that the minimum is 5 ticks.

Copy pasted from the docs:

[in]	timeout_ticks	Number of ticks (of RTC1, including prescaling) to timeout event minimum 5 ticks).

[sowmya]

Thank you for the link. I changed the value from 5 to 1 and created only one timer instance. But I am getting 30ms instead of 10ms. Will it effect if I change the Number of ticks ?

[Anders Strand]

The number of ticks is what the clock "counts" to before triggering your callback function. With a prescaler of 327, the clock counts 100 times per second (or 100 ticks per second). 1 tick is then 10 ms. 5 ticks is therefore 50 ms. How do you measure the time before callback is triggered?

If you want a 10ms timer. Set the prescaler lower(maximum 65), to count faster. Use the APP_TIMER_TICKS macro to convert from ms to ticks.

[sowmya]

Yes correct. 1 tick corresponds to 10 ms with prescale of 327. And I want to achieve 10 ms interrupt. I am toggling a pin for each interrupt callback.