Share pin between SAADC and digital interface

RE: Share pin between SAADC and digital interface

Jørgen Holmefjord — Thu, 10 Feb 2022 10:07:01 GMT

I have created internal tickets to look into peripheral documentation and clearing pins in nrfx_saadc_uninit_v2_api.

RE: Share pin between SAADC and digital interface

Tomasz K — Thu, 10 Feb 2022 07:33:37 GMT

Hi, thanks for an answer.
It makes complete sense and also matches what I observed. Indeed docs are slightly misleading here.

I'm using currently nRF SDK 17.1.0 which supports two nrfx_saadc implementations.
Older one indeed clears channel configuration on uninit:

nrf_saadc_disable();
m_cb.adc_state = NRF_SAADC_STATE_IDLE;

for (uint32_t channel = 0; channel < NRF_SAADC_CHANNEL_COUNT; ++channel)
{
    if (m_cb.psel[channel].pselp != NRF_SAADC_INPUT_DISABLED)
    {
        nrfx_err_t err_code = nrfx_saadc_channel_uninit(channel);
        NRFX_ASSERT(err_code == NRFX_SUCCESS);
    }
}

However, the newer one (called API_v2) doesn't have it implemented:

nrfx_saadc_abort();
NRFX_IRQ_DISABLE(SAADC_IRQn);
nrf_saadc_disable();
m_cb.saadc_state = NRF_SAADC_STATE_UNINITIALIZED;

To do it the way you suggest, I would have to call "nrfx_saadc_channels_config" with all previously used pins set to "NRF_SAADC_INPUT_DISABLED" and then uninit saadc which isn't really intuitive.

As far as I see, nrfx_saadc implementation available on github has already "nrfx_saadc_channels_deconfig" implemented, which does exactly what is needed, however there is no information available that it needs to be called and it's also not automatically called on uninit.

Maybe it will be good idea to write separate ticket for it, so it can be modified or better explained in future releases?

Thanks again for help, I will implement it and give it a go.

Best regards
Tomasz

RE: Share pin between SAADC and digital interface

Jørgen Holmefjord — Wed, 09 Feb 2022 16:40:04 GMT

Hi,

As far as I can see, the analog pins are acquired as soon as they are configured in the PSELP/PSELN registers, not when the SAADC->ENABLE register is set. Similar, the analog pins are released when the PSELP/PSELN registers are cleared.

The comment in the ENABLE register documentation may thus be a bit inaccurate, as the ENABLE register does .

Our SAADC driver clears the pin config in the uninit-function, and I would recommend you do the same in your application when you want to use the pins for digital peripherals.

Best regards,
Jørgen