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SAADC callback

RichieJH

I have this working and producing good and accurate results, but I'm still puzzled by some of the examples in the SDK and the documentation.

I am using the processor to call for the saadc sample (i.e, not ppi) and I set the nrf_drv_saadc_buffer_converts immediately before hand:

err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAMPLES_IN_BUFFER);
err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1], SAMPLES_IN_BUFFER);
err_code = nrf_drv_saadc_sample();

In the examples in the SDK (12) and elsewhere I also see another nrf_drv_saadc_buffer_convert call in the callback handler prior to reading the data in the buffer:

err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);

My question is what is the point of calling this again in the call back and why is the first argument p_event->data.done.p_buffer? I've read the documentation but it still doesn't make sense to me. Could anyone explain this as if they are speaking to a 5 year old?

Many thanks,

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    In this example if should not matter, as there is only one channel active, space for 5 samples in each buffer, and a sampling rate of once every 400ms. Due to the double buffering, the second buffer will be used for sampling when the first buffer is full. The data in the buffer will not be erased, as it only use a pointer to the memory location, and it will neither be overwritte until the second buffer is full, meaning 2 seconds after you get the callback, leaving you plenty time to read the buffer. In a more high-speed sample application, I would suggest reading the buffer before setting it up for conversion again to avoid loss of samples.

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    In this example if should not matter, as there is only one channel active, space for 5 samples in each buffer, and a sampling rate of once every 400ms. Due to the double buffering, the second buffer will be used for sampling when the first buffer is full. The data in the buffer will not be erased, as it only use a pointer to the memory location, and it will neither be overwritte until the second buffer is full, meaning 2 seconds after you get the callback, leaving you plenty time to read the buffer. In a more high-speed sample application, I would suggest reading the buffer before setting it up for conversion again to avoid loss of samples.

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