SAADC callback

RE: SAADC callback

Jørgen Holmefjord — Mon, 19 Jun 2017 07:16:54 GMT

Yes, you are correct.

RE: SAADC callback

JisongXie — Sat, 17 Jun 2017 13:18:27 GMT

Hi, Jorgen, I want to ask whether you mean that

read samples and fill in the buffer[0] ---> 2. buffer[0] is full and callback, but the sample is not stop and it fill in the buffer[1] ---> 3. the callback has been done, while maybe the buffer[1] hasn't been full ----> 4. the buffer[1] is full and callback, but the sample is not stop and it fill in the buffer[0] --->> Am I right?? Thank you very much!

RE: SAADC callback

acha — Tue, 02 May 2017 09:35:41 GMT

Yess, when B and C are floating and a tension in channel A, I have unstable reading in the channel B when I set a tension in the channel A, when I set a tension in channel B, I have unstable reading in channel C, when I set tension in the channel C, I dont have instable reading o_O.

RE: SAADC callback

Jørgen Holmefjord — Tue, 02 May 2017 09:31:34 GMT

If you have not connected channel B it will be floating, giving you unstable reading. What are you trying to achieve with this? Are you getting wrong reading if you connect the channel before measurement?

RE: SAADC callback

acha — Tue, 02 May 2017 09:30:10 GMT

there is my callback :

void adcHandler(nrf_drv_saadc_evt_t const *p_event) { if (p_event->type == NRF_DRV_SAADC_EVT_DONE) { nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);

            adc_result = p_event->data.done.p_buffer[0];
            ptrFcnArray[0](adc_result); // Function which handles result in channel 0.
        
            adc_result = p_event->data.done.p_buffer[1];
            ptrFcnArray[1](adc_result); // Function which handles result in channel 1.           

            adc_result = p_event->data.done.p_buffer[2];
            ptrFcnArray[2](adc_result); // Function which handles result in channel 2.
}

}

RE: SAADC callback

acha — Tue, 02 May 2017 09:27:50 GMT

That's what I'm testing actually, the problem that I have a static error in one or ther channel, if I set for example 3.3 V in channel A, I have about 1.2V in the channel B, i the time the B channel is not connected :/

RE: SAADC callback

Jørgen Holmefjord — Tue, 02 May 2017 09:25:22 GMT

Yes, this is correct.

RE: SAADC callback

acha — Tue, 02 May 2017 09:20:19 GMT

Hello all, I have question about buffer filling, if there is multiple channels initialized for conversion, that's means that p_event->data.done.p_buffer[0] contains the converted value for first channel enabled, p_event->data.done.p_buffer[1] for the second one, and p_event->data.done.p_buffer[2] for the third one?

RE: SAADC callback

Jørgen Holmefjord — Thu, 30 Mar 2017 12:36:35 GMT

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.

RE: SAADC callback

RichieJH — Thu, 30 Mar 2017 10:26:51 GMT

Ok, thanks. So am I correct in thinking that the reason it is fine to set up that buffer again before reading the data in the buffer is that it won't be overridden until a sample is triggered once more? So setting up the buffer could be done either before or after reading the data in the buffer?

RE: SAADC callback

Jørgen Holmefjord — Thu, 30 Mar 2017 09:37:49 GMT

Hi,

The SAADC of nRF52 support double buffering, meaning you can have two buffers setup for conversion where one is processed while the other is used for sampling.

When you call

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);

you setup two buffers.

When one of the buffers is full, you will get a callback. You now have to setup the buffer for sampling again, if not, your application will not have a buffer available for sampling.

The reason the first argument is p_event->data.done.p_buffer is that this is a pointer to the buffer that is full and caused the callback. By using this as the argument, the same buffer will be setup for conversion.

Best regards,

Jørgen