Calibrating SAADC on nrf52832

RE: Calibrating SAADC on nrf52832

Kenneth — Mon, 01 Mar 2021 14:20:11 GMT

Have you taken a look at this repository:
https://github.com/NordicPlayground/nRF52-ADC-examples/tree/master/nrfx_saadc_simple_low_power_app_timer_multichannel_oversample

Kenneth

RE: Calibrating SAADC on nrf52832

N Ashelman — Mon, 01 Mar 2021 02:54:44 GMT

Thanks for sharing your experiences. Indeed, as you found, I can get calibration to run successfully once at startup (but not again), but I too am not observing much improvement. Without calibration, I am measuring GROUND at -1 to -2 raw value (10-bit). Calibration will sometimes bring this to zero, but sometimes not. Have not tried yet under temperature variations.

If you are able to dig up the old code, it might be of use to me & others using this ticket in the future. It seems to come up pretty high in search results :-)

RE: Calibrating SAADC on nrf52832

Franz — Sat, 27 Feb 2021 17:19:25 GMT

Hi!

I would have to check next week since I do not remember the exact code that I used to get rid of the described error. I only remeber that I changes my ADC code to only have one channel enabled at a time. I can send you the piece in a few days if you whish. One BIG word of caution, though.

Although I managed to get rid of the error and calibration in regular interval does not throw errors, I have the feeling that calibration does not work at all on the 52832. Of course I cannot prove that or be sure, but we invested a lot of time to measure the code the adc delivers on a number of boards under controlled thermal conditions and we had one devkit with nrf52832 where the calibration even made things worse than without any calibration.

I had another private ticket open on a similar topic because of confidential code, but we never managed to get rid of problems with bad performance of calibration (we have "jumps" in the signal of about 6 LSB12b, which might be ok from a datasheet perspective, but does defeat the purpose of the calibration unless you use a very wide temperature range).

RE: Calibrating SAADC on nrf52832

N Ashelman — Fri, 26 Feb 2021 09:56:09 GMT

Hi Franz:
I have used the example code for calibrate_saadc() and having the same NRFX_ERROR_INVALID_STATE problem you reported earlier. Could you give some more details about how you solved this?
How can calibration be so hard? Looks like it's time for Nordic to add a library on top of the driver to support this kind of stuff...

RE: Calibrating SAADC on nrf52832

Franz — Sun, 08 Sep 2019 13:11:54 GMT

Problem was the missing workaround of PAN86, among one additional code bug.. closed

RE: Calibrating SAADC on nrf52832

Kenneth — Mon, 10 Dec 2018 16:01:00 GMT

I am not sure what more debugging that can be done from here, but looking at the code it seems that nrfx_saadc_sample() will report NRFX_ERROR_INVALID_STATE if m_cb.adc_state != NRF_SAADC_STATE_BUSY.

So maybe your first task is to set a breakpoint when err_code = NRFX_ERROR_INVALID_STATE; in nrfx_saadc_sample() to find the actual value of m_cb.adc_state. And then you can add a log output every time m_cb.adc_state is set to the specific value to find which function is called that set it to !NRF_SAADC_STATE_BUSY in this case.

Best regards,
Kenneth

RE: Calibrating SAADC on nrf52832

Franz — Mon, 10 Dec 2018 10:26:37 GMT

Hi Kenneth,

It´s been some time. any update to this?

RE: Calibrating SAADC on nrf52832

Franz — Wed, 17 Oct 2018 06:29:28 GMT

Hi Kenneth,

Well sorry, I could have found out that for myself. My program crashed around the line, where the ADC is initilaised with "NULL", so I was a bit blinded but actually, the crash happened somwhere else.

However, back to the main topic of my question: I still have troubles using the offset calibration. My program does essentially the same as your provided example code and more specifically, it uses the exact code of the "calibrate_saadc" function.

Unfortunately, when i have the call to the calibrate function in my code (right after nrfx_saadc_init), the program hangs in "nrfx_saadc_sample()" with "NRFX_ERROR_INVALID_STATE" after the first adc conversion (1 sample per CH) is complete.

This does not happen when I comment the line with the call to the calibrate function during adc initialisation.

Any hints?

RE: Calibrating SAADC on nrf52832

Kenneth — Tue, 16 Oct 2018 16:24:41 GMT

It is example code so please change this as you see fit, but basically using NULL will set default settings from sdk_config.h

__STATIC_INLINE ret_code_t nrf_drv_saadc_init(nrf_drv_saadc_config_t const * p_config,
                                              nrf_drv_saadc_event_handler_t  event_handler)
{
    if (p_config == NULL)
    {
        static const nrfx_saadc_config_t default_config = NRFX_SAADC_DEFAULT_CONFIG;
        p_config = &default_config;
    }
    return nrfx_saadc_init(p_config, event_handler);
}

RE: Calibrating SAADC on nrf52832

Franz — Tue, 16 Oct 2018 11:46:43 GMT

E.g. line number 99 in the code example you shared above.

RE: Calibrating SAADC on nrf52832

Kenneth — Tue, 16 Oct 2018 06:59:20 GMT

About 5) What file and line number are you referring to?

Kenneth

RE: Calibrating SAADC on nrf52832

Franz — Tue, 16 Oct 2018 05:51:43 GMT

Hi Kenneth,

Thanks for the reply.

According to the numbering of my initial questions:

3.) Good to know, so it is no problem with IR processing because the delay until the IR is handled, is big enough in any case?

4.) Will have to check where in the forum I saw it, I will come back to that.

5.) Well there is one thing I want to ask about this example which is also somthing I did not understand in another example: How is the call to err_code = nrf_drv_saadc_init(NULL, saadc_callback); supposed to work?

I use nrfx_saadc_init(NULL,saadc_callback); according to the new API in SDK V15, but there is a line in the function "nrfx_saadc_init(NULL,saadc_callback);" that obviously returns immediately if the function is called with a NULL pointer. What is the reason for nto initialising with a proper "ADC config structure" ?

Thanks

RE: Calibrating SAADC on nrf52832

Kenneth — Mon, 15 Oct 2018 13:28:49 GMT

Hi,

[quote user=""]Do I have to do a dummy TASK_SAMPLE before calling the abort function so that a conversion is in progress?[/quote]

See this case: https://devzone.nordicsemi.com/f/nordic-q-a/29806/nrf52832-sdk14---saadc-calibration-issues

1. You should implement according to Errata 86 if you are using calibrate offset yes.

2. This is already handled in nrfx_saadc_abort().

3. The transfer to RAM may be a problem if you are directly using this as a pointer value for other peripheral, e.g. have a saadc done event to uart start tx task. But for interrupt processing it's not a problem.

4. Not sure if I see that, what examples project and source file are you referring to?

5. A colleague made this example, maybe it can help you also:

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/** @file
 * @defgroup nrf_adc_example main.c
 * @{
 * @ingroup nrf_adc_example
 * @brief ADC Example Application main file.
 *
 * This file contains the source code for a sample application using ADC.
 *
 * @image html example_board_setup_a.jpg "Use board setup A for this example."
 */

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include "nrf.h"
#include "nrf_drv_saadc.h"

#include "boards.h"
#include "app_error.h"
#include "nrf_delay.h"
#include "app_util_platform.h"
#include "nrf_pwr_mgmt.h"

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

#define SAMPLES_IN_BUFFER 5
#define HW_TIMEOUT 10000


nrf_saadc_value_t m_buffer_pool[2][SAMPLES_IN_BUFFER];

void calibrate_saadc(void);

void saadc_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);

        for (uint8_t i = 0; i < SAMPLES_IN_BUFFER; i++)
        {
            NRF_LOG_INFO("%d", p_event->data.done.p_buffer[i]);
        }
    }
}


void saadc_init(void)
{
    ret_code_t err_code;
    nrf_saadc_channel_config_t channel_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);

    err_code = nrf_drv_saadc_init(NULL, saadc_callback);
    APP_ERROR_CHECK(err_code);

    calibrate_saadc();

    err_code = nrf_drv_saadc_channel_init(0, &channel_config);
    APP_ERROR_CHECK(err_code);

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

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);
}

void calibrate_saadc(void)
{
    nrfx_err_t nrfx_err_code = NRFX_SUCCESS;

    // Stop ADC
    nrf_saadc_int_disable(NRF_SAADC_INT_ALL);
    NRFX_IRQ_DISABLE(SAADC_IRQn);
    nrf_saadc_task_trigger(NRF_SAADC_TASK_STOP);

    // Wait for ADC being stopped.
    bool result;
    NRFX_WAIT_FOR(nrf_saadc_event_check(NRF_SAADC_EVENT_STOPPED), HW_TIMEOUT, 0, result);
    NRFX_ASSERT(result);

    // Start calibration
    NRFX_IRQ_ENABLE(SAADC_IRQn);
    nrfx_err_code = nrfx_saadc_calibrate_offset();
    APP_ERROR_CHECK(nrfx_err_code);
    while(nrfx_saadc_is_busy()){};
    
    // Stop ADC
    nrf_saadc_int_disable(NRF_SAADC_INT_ALL);
    NRFX_IRQ_DISABLE(SAADC_IRQn);
    nrf_saadc_task_trigger(NRF_SAADC_TASK_STOP);

    // Wait for ADC being stopped. 
    NRFX_WAIT_FOR(nrf_saadc_event_check(NRF_SAADC_EVENT_STOPPED), HW_TIMEOUT, 0, result);
    NRFX_ASSERT(result);
    
    // Enable IRQ
    NRFX_IRQ_ENABLE(SAADC_IRQn);

}


/**
 * @brief Function for main application entry.
 */
int main(void)
{
    uint32_t err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();

    ret_code_t ret_code = nrf_pwr_mgmt_init();
    APP_ERROR_CHECK(ret_code);

    saadc_init();

    NRF_LOG_INFO("SAADC calibration example started.");

    while (1)
    {
        nrf_pwr_mgmt_run();
        NRF_LOG_FLUSH();
    }
}


/** @} */