PWM failed to work with SoftDevice 8.0 in nRF51822

RE: PWM failed to work with SoftDevice 8.0 in nRF51822

ovrebekk — Thu, 18 Jun 2015 07:47:35 GMT

The SoftDevice API's (sd_ppi_... for instance) will only work after the SD is enabled, which is why you have to initialize PWM after the SD when setting USE_SOFTDEVICE = 1 in the PWM library.

When USE_SOFTDEVICE = 0 the PWM driver will access peripherals such as NRF_PPI directly, and if you try to do this when the SD is enabled you will get a hard fault. That is why the advice earlier was to initialize the PWM driver before the SD, so that the PPI configuration would work.

Now that the USE_SOFTDEVICE define is added you should just use this when using PWM with the SD.

Regards Torbjørn

RE: PWM failed to work with SoftDevice 8.0 in nRF51822

diode — Wed, 17 Jun 2015 17:13:39 GMT

Hi Øyvind, your advice works. I also found that the libraries in this post just don't work, no matter I call pwm_init() before or after ble_stack_init(). For this repo, it only works if calling pwm_init() after ble_stack_init(). Why is the calling sequence reversed here?

RE: PWM failed to work with SoftDevice 8.0 in nRF51822

JohnBrown — Wed, 17 Jun 2015 09:02:52 GMT

I don't know why your code is not working, but if you are really only looking to produce a square wave, i.e constant 50% duty cycle(or any other constant duty cycle, which would more accurately be described as a rectangular wave), and at a constant frequency, I would write the thing myself, using a counter timer and GPIOTE.

If you are hoping to vary either the duty or the frequency on the fly, then good luck with that.

It is, in my humble opinion, a weakness of the nRF51822, in that the compare registers are not double buffered, and you can not have a SET and a CLEAR task directed to a single I/O pin, but have to rely on a TOGGLE instead. I say this as someone who has fought with this in a quest to reliably produce DTMF tones WITHOUT the SD running!

However, I suppose the designers have tough choices to make about the best use of silicon...

RE: PWM failed to work with SoftDevice 8.0 in nRF51822

Øyvind Karlsen — Wed, 17 Jun 2015 08:50:56 GMT

Hi,

If you're using the code from this repo, pwm_init() should be called after the soft device has been initialized. Hopefully this solves your problem.

Best regards,

Øyvind