SAADC Scan Mode mixes channel buffers whan fast.

RE: SAADC Scan Mode mixes channel buffers whan fast.

schef — Mon, 20 Mar 2017 06:32:06 GMT

I use timer for microphone to measure noise. Which needs to be measured through period of 30s.

RE: SAADC Scan Mode mixes channel buffers whan fast.

Hung Bui — Wed, 15 Mar 2017 12:43:31 GMT

@schef:I don't understand why you need a timer here, I assume you only need one sample per channel ? The saadc example we used the timer just to show how this can be done automatically and periodically with the help of EasyDMA. I'm not sure you need that for your use case.

RE: SAADC Scan Mode mixes channel buffers whan fast.

schef — Wed, 15 Mar 2017 06:14:16 GMT

Here is what i have now and works for me. Didnt have a crash yet.

I have one saadc_sampling_event_init which has a timer in it. For each channel i have separate callback and saadc_init function.

I have created a function

void saadc_uninit(void)
{
  nrf_drv_saadc_uninit();
}

which i call after the measurement.

So for example one procedure may look like this.

void saadc_battery_level_callback(nrf_drv_saadc_evt_t const * p_event)
{
  if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
  {
    ret_code_t err_code;
    err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER); APP_ERROR_CHECK(err_code);
    //SEGGER_RTT_printf(0, "buffa: %d\n", p_event->data.done.p_buffer[0]);
    battery_level_saadc_value = (uint16_t)caluclate_average_result(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);
    set_data_ready(true);
  }
}

void battery_channel_enable()
{
  saadc_battery_level_init();
  saadc_sampling_event_enable();
}

void battery_channel_disable()
{
  saadc_sampling_event_disable();
  saadc_uninit();
}

static void wait_for_sample_data()
{
  while(!is_data_ready())
  {
    nrf_delay_ms(1);
    __WFE();
    __SEV();
    __WFE();
    nrf_delay_ms(1);
  }
  set_data_ready(false);
}


uint16_t get_battery_saadc_sample()
{
  battery_channel_enable();
  wait_for_sample_data();
  battery_channel_disable();
  return(battery_level_saadc_value);
}

What do you think about nrf_delay_ms(1);. If i remove them i never got the data_ready.

RE: SAADC Scan Mode mixes channel buffers whan fast.

schef — Wed, 15 Mar 2017 06:03:58 GMT

I have 3 sensors. 1. is the IR sensor, 2. the microphone and 3. the battery measurement. IR sensor gave me around 400 and reacted to my movement. The microphone was around 1500 and the battery around 2200. So I took 3 channel but used one SEGGER_RTT_printf with filter like these: if (i % 3 == 0) SEGGER_RTT_printf(0, "fill: %d: %d\n", i, p_event->data.done.p_buffer[i]);. Now. When i was measuring at the timer rate of 50us it was mixed (i got sometimes 2000, sometimes 1500, sometimes 400) but when i used 200us it NEVER got mixed up. So that was my conclusion.

RE: SAADC Scan Mode mixes channel buffers whan fast.

Hung Bui — Tue, 14 Mar 2017 16:02:34 GMT

@schef: Could you describe a little bit more what kind of mixed up /crash you got ?

What was your source resistance ? This can affect the acquisition time as in 37.12.1 in the spec, and the time there is for each SAMPLE task.

When do you print the result out with RTT ? If you printout on every sample you got it may cause a problem since it's not enough time to print I assume.

RE: SAADC Scan Mode mixes channel buffers whan fast.

tkorsdal — Mon, 13 Mar 2017 15:21:50 GMT

If your source impedance allows it (See 37.9) you can lower the acquisition time (CH[x].CONFIG).

You could maybe also have an "activated_channel_mask" that you update in the SAADC_EVENTS_END handling by enabling/disabling SAADC channels and interpret the content of the DMA buffer accordingly. (Haven't tried this myself though).

RE: SAADC Scan Mode mixes channel buffers whan fast.

schef — Mon, 13 Mar 2017 13:19:53 GMT

Thank you for pointing me to this section. What do you suggest on doing else? I don't need all three channels at the sametime. But i tought it would be much cleaner to init saadc once then using the tehnique of loop {init, sample, deinit}

I had a crash after many times of doing this. With signal interrupt and no backtrace.

RE: SAADC Scan Mode mixes channel buffers whan fast.

tkorsdal — Mon, 13 Mar 2017 12:23:28 GMT

Yes it is possible - I have seen the same. You must have enough time between sample events to allow 3 acquisitions and 3 conversions. See 37.5.2 og nRF52832 Product Specification.

RE: SAADC Scan Mode mixes channel buffers whan fast.

schef — Mon, 13 Mar 2017 11:41:34 GMT

I use: if (i % 3 == 0) SEGGER_RTT_printf(0, "fill: %d: %d\n", i, p_event->data.done.p_buffer[i]); if (i % 3 == 1) SEGGER_RTT_printf(0, "noise: %d: %d\n", i, p_event->data.done.p_buffer[i]); if (i % 3 == 2) SEGGER_RTT_printf(0, "battery: %d: %d\n", i, p_event->data.done.p_buffer[i]); ` to view the results.