BAS with SAADC - How to read ADC value periodically

RE: BAS with SAADC - How to read ADC value periodically

Jørgen Holmefjord — Thu, 01 Jun 2017 07:12:36 GMT

There should not be any difference in using nrf_drv_saadc_gpio_to_ain(4) or NRF_SAADC_INPUT_AIN2 directly. The gpio_to_ain function only returns the correct index of the nrf_saadc_input_t enum, to get corresponding NRF_SAADC_INPUT_AINx value. Note that this reflects the Analog input, not the GPIO pin number, i.e., AIN2 = GPIO P0.04.

RE: BAS with SAADC - How to read ADC value periodically

MANGO — Thu, 01 Jun 2017 00:52:27 GMT

Pardon me, Jørgen.

In the SDK 12.1 infocenter's explanation, it says configures one channel to sample analog input 0 (GPIO pin 2).

The original code was

channel_config = NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(nrf_drv_saadc_gpio_to_ain(2));

whereas the nrf_saadc_input_t enums uses a different value.

#define SAADC_CH_PSELP_PSELP_AnalogInput0 (1UL) /*!< AIN0 */
#define SAADC_CH_PSELP_PSELP_AnalogInput2 (3UL) /*!< AIN2 */
typedef enum {
NRF_SAADC_INPUT_AIN0     = SAADC_CH_PSELP_PSELP_AnalogInput0, ///< (AIN0).
NRF_SAADC_INPUT_AIN2     = SAADC_CH_PSELP_PSELP_AnalogInput2, ///< (AIN2).

Should I use NRF_SAADC_INPUT_AIN2 + 1? This looks quite weird. I added a photo to the original question.

-Best Regards

RE: BAS with SAADC - How to read ADC value periodically

Jørgen Holmefjord — Wed, 31 May 2017 11:07:15 GMT

Blocking/non-blocking mode is described in the SAADC documentation. Blocking mode will simply wait for the function to finish, before continuing the program. In non-blocking mode, you start a task, allowing the CPU to continue other work/sleep. When the task is completed, a interrupt or event will be generated, allowing the CPU to process the result.

RE: BAS with SAADC - How to read ADC value periodically

MANGO — Wed, 31 May 2017 10:59:33 GMT

Hi, Jørgen. Thanks for your quick reply! Can I ask you about the technical term?

I always wondered the "blocking / non-blocking" mode.

Is this similar to the ARM's thumb mode? Or is this a mode defined by Nordic?

I couldn't find that term at the product spec or the Nordic's infocenter.

-Best regards

RE: BAS with SAADC - How to read ADC value periodically

Jørgen Holmefjord — Wed, 31 May 2017 09:23:42 GMT

Hi,

If you want to get a single sample from the SAADC, you can use blocking mode with the function nrf_drv_saadc_sample_convert(). This can be called in your timer callback, and you can use the sample value to update the BAS characteristics.

I still think it is a better solution to use non-blocking sampling and trigger the sample task from the timer callback (or connect the timer event directly to the sample task using PPI), if you will be doing regular sampling. You can set the buffer size to 1 to get a callback after each sample.

Your channel setup looks correct, but if you only use one SAADC channel, you can use channel 0. It is also possible to use the AIN2 define from nrf_adc.h as an input directly, this depends on what you think is more easily readable:

NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN2);
err_code = nrf_drv_saadc_channel_init(0, &channel_config);

Best regards,

Jørgen