Avoid SDK modules who need app timers

[ppatierno]

Hello,

I'm developing an application that will run on a board without externel oscillator for RTC1 and it means no app timers support. I started from ANCS example and I see that it uses following modules that needs app timers :

• BSP for buttons and leds;
• BLE conn params;
• scheduler;

What's the suggested why to have above features but without app timers ? Is the scheduler needed ?

Thanks, Paolo

[Susheel Nuguru]

Normally with softdevice, you select the LFCLK when you call SOFTDEVICE_HANDLER_INIT

In your case you call for example

SOFTDEVICE_HANDLER_INIT(NRF_CLOCK_LFCLKSRC_RC_250_PPM_4000MS_CALIBRATION, NULL);

Then softdevice will start the LFCLK for your application. If your application does not use softdevice then you can do this in your app like below

NRF_CLOCK->LFCLKSRC            = (CLOCK_LFCLKSRC_SRC_RC << CLOCK_LFCLKSRC_SRC_Pos);
NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
NRF_CLOCK->TASKS_LFCLKSTART    = 1;

while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0)
{
    // Do nothing.
}
    
APP_TIMER_INIT(APP_TIMER_PRESCALER, APP_TIMER_MAX_TIMERS, APP_TIMER_OP_QUEUE_SIZE, NULL);

And the APP_TIMER will use internal oscillator, you just need to select and start the LFCLK once

[Susheel Nuguru]

copy paste from reference manual about the options you have to choose from for LFCLK

LFCLK clock controller
As illustrated in Figure 15 the system supports the following low frequency clock sources:
• LFCLK crystal oscillator: 32.768 kHz crystal oscillator
• LFCLK RC oscillator: 32.768 kHz RC oscillator
• LFCLK synthesizer: 32.768 kHz synthesized from HFCLK

If you do not have the first one on your product, you can choose the others. Read about clocks before you make major changes to your code.

[ppatierno]

Great to know Aryan !

I'm using SoftDevice S130 and I was scaried that without external oscillator (on our target board for a wereable) I couldn't use the great app timers feature. Now I know that I can use them for my project.

Thanks, Paolo

[bloobird0]

Hello, what is the softdevice is present but not activated, LFCLK started manually like described above and later SOFTDEVICE_HANDLER_INITis called. Is there any probleme there that the SoftDevice tries to start a clock that is already in use by app_timer?

[Sumanth Murali]

Starting LF clock using nrf_drv_lf_clk_request() instead of SOFTDEVICE_HANDLER_INIT changes the timing of the system. Interrupts come in at a different rate. Any idea why this could be happening?

[Susheel Nuguru]

When softdevice is enabled using it will use the RTC0 interrupts for time keeping with highest priority. So your application timers will be affected with it since your application timers are running with lower priority than softdevice timer (RTC0)

What you see is normal