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Explanation of pwm example code please

Hi, I need to configure pwm with 14uSec off time and 46uSec on time. I had a look at the pwm example in the install directory and also : developer.nordicsemi.com/.../a00039.html. But it is bit confusing, in the sense, if I need to set a duty cycle of 25% which registers to change. When I change the duty_cycle to 250, or, 100(in the local variable "duty_cycle"), there is no effect in the PWM wave generated. The On and Off times are 256msec always. Even tried pressing the configured buttons, but still no change in duty cycle. Attached my code here: main.c

Questions:

  1. Which register to change to set a desired duty cycle(say 25% off time and 75% on time)
  2. If I want to use the same PWM module for generating 25% duty cycle outputting on PIN1 for the first time, then 100% duty cycle outputting on PIN2 the next time and the above continues forever, do I need to deinit the gpiote and configure(nrf_gpio_tsk_config) every time I swap the PWM pins?
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  • As the code is now BLE interrupts can invert the PWM if the TIMER_IRQHandler is interrupted an a toggle is missed (for example if a BLE interrupt lasting longer than MAX_SAMPLE_LEVELS happen just before if(cc0_turn)).

    The PWM library does not have this problem, but with this library you can only set the duty cycle of the PWM and not the frequency. I would use this library if you can, if not you will have to find out a clever way to update the PWM without risking invertions or dissortions in the signal. One way is to stop the timer, update the CC values and then start the timer again, this will avoid invertion, but will create a long low or high pulse on the line.

Reply
  • As the code is now BLE interrupts can invert the PWM if the TIMER_IRQHandler is interrupted an a toggle is missed (for example if a BLE interrupt lasting longer than MAX_SAMPLE_LEVELS happen just before if(cc0_turn)).

    The PWM library does not have this problem, but with this library you can only set the duty cycle of the PWM and not the frequency. I would use this library if you can, if not you will have to find out a clever way to update the PWM without risking invertions or dissortions in the signal. One way is to stop the timer, update the CC values and then start the timer again, this will avoid invertion, but will create a long low or high pulse on the line.

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