sdk11 pwm frequency control

[HakJae]

Hi, i used sdk11 and softdevice version s130_2.0.

And i used pwm library.

i try to make pwm pulse accurate 38khz.

When i used sdk 6.0, i could control timer used to prescaler and cc[0].

but sdk 11, i couldn't find prescaler and cc[0].

i want to control timer period.

What can i do to control pwm pulse ?

[Stefan Birnir Sverrisson]

Hi

For reliable PWM, use the PWM library in SDK 11. The PWM library uses TIMER peripheral in the background. There is a library function app_pwm_channel_duty_set to set the duty cycle. To set the PWM period, configure app_pwm_config_t.period_us before initializing the PWM library. There is pwm_library example in SDK 11.

[Stefan Birnir Sverrisson]

ok, I see your point.

To get 38.0 kHz, I suspect you need timer prescaler as = 0 to have the base frequency of the timer as 16MHz

The desired timer ticks are therefore 16MHz/38khz=421=0x1A5. In order to set the TIMER CC value as 0x1A5, you could hardcode that in the app_pwm.c -> app_pwm_init function. Instead of calling nrf_drv_timer_us_to_ticksin line 777, just set ticks = 0x1A5;