SAADC only fills sample buffer with one sample per channel on each trigger

[tommy.lane]

The documentation on the SAADC peripheral driver is unclear about how the samples are handled. When I read the docs I was under the impression that when providing a multiple of the number of sample channels to the ADC the ADC would trigger "automatically" back to back until the sample buffer was full.

However, what actually happens is that the ADC handler is only called when the sample buffer is filled, and a single sample per channel is taken during each ADC sample trigger event.

[Jørgen Holmefjord]

Hi,

Can you point to the part of documentation that confuse you? The SAADC peripheral documentation is quite clear on this:

In scan mode, one SAMPLE task will trigger one conversion per enabled channel.

To me, this is also understandable from the SDK driver  doucmentation:

To trigger sampling, call the function nrf_drv_saadc_sample or, through PPI, use the task SAMPLE from SAADC. nrf_drv_saadc_sample_task_get can be used to get the task address. Single sampling triggers conversion on all initialized channels. When the requested buffer is filled with samples, an event of type NRF_DRV_SAADC_EVT_DONE is generated.

Best regards,
Jørgen

[tommy.lane]

Jørgen Holmefjord said:

When the requested buffer is filled with samples, an event of type NRF_DRV_SAADC_EVT_DONE is generated.

Looking at it now it's obviously what it means. When I initially read this section the "[when filled with samples]" section seemed out of place, and unnecessary. If the goal of this sentence is to convey that each sample event only fills one sample location per channel then clearly stating "Each sampling event only fills a single array index per channel during the acquire event, when the requested buffer is filled with samples, an event of type NRF_DRV_SAADC_EVT_DONE is generated."

Wording could use some work, but this is roughly how I feel it should read.

Thanks for getting back to me so quickly!