Higher frequency response from app_pwm_library

[SentinelLighting]

I implemented the app_pwm_library, but it seems to "top out" at 500Khz?  Here is a summary of my code.  Is there a set of routines that have a higher speed?

APP_PWM_INSTANCE(PWM1,1);            // Create the instance "PWM1" using TIMER1.

...

ret_code_t err_code;

/* 1-channel PWM, 2 us (500khz)*/
app_pwm_config_t pwm1_cfg = APP_PWM_DEFAULT_CONFIG_1CH(2, PWM_PIN);
/* Initialize and enable PWM. */
err_code = app_pwm_init(&PWM1, &pwm1_cfg, 0);
APP_ERROR_CHECK(err_code);
...

app_pwm_enable(&PWM1);

...

while (app_pwm_channel_duty_set(&PWM1, 0, value) == NRF_ERROR_BUSY);

Thanks for any help!

[Vidar Berg]

Hi,

This library realizes pwm by using GPIOTE+PPI+TIMER instead of using one of the dedicated PWM instances available on the 52 series. At least for the 51, the max. frequency was 200 Khz (higher frequency may cause glitches on the output). I would recommend you to use the "pwm_driver" example if you're developing code for the 52 series. 

[SentinelLighting]

Thanks Vidar, I will look at the pwm_driver code.  Could you give me guidance on how I might be able to drive multiple output pins from the same PWM?  Do I need to use the GPIOTE and PPI?

[Vidar Berg]

You can drive up to 4 pins per PWM instance (52832 has 3) as demonstrated by the pwm driver example (nRF5_SDK_15.2.0_9412b96\examples\peripheral\pwm_driver). 

GPIOTE is not necessary, but you may use PPI to trigger PWM to start.  

EDIT: forgot to add that there are some pins that you should avoid using for high frequency signals as the may interfere with the radio. Please refer to the pin assignment sections in the PS for the chip package you have to find out which pins have this restriction.