I need to digitize one input every 10 usec and store results into memory. After say 100000 samples the ADC should stop.
Thanks
I need to digitize one input every 10 usec and store results into memory. After say 100000 samples the ADC should stop.
Thanks
Hi,
You should be able to achieve this with the SAADC example from the SDK with only minor modifications. You need to lower the acquisition time to 5 us in order to take a sample every 10 us (as the SAADC also has a 2 us conversion time for each sample). The timer must be changed to trigger every 10 us, and you need a counter to know when to stop sampling. It is also a good idea to increase the buffer size, to reduce the number of interrupts. The SAADC peripheral can accept buffer sizes up to 32767 samples in a single buffer.
I attached a sample main.c that you can replace in the SAADC example. It does stop the timer and disable PPI channel after 100 events of buffer size 1000 samples are received, but it does not disable/uninitialize the SAADC peripheral. The example also re-uses the same two 1000 sample buffers over and over. If you need to store all samples in RAM, you can use 100 different buffers of 1000 samples each that you setup using the nrf_drv_saadc_buffer_convert() function.
/**
* Copyright (c) 2014 - 2020, Nordic Semiconductor ASA
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form, except as embedded into a Nordic
* Semiconductor ASA integrated circuit in a product or a software update for
* such product, must reproduce the above copyright notice, this list of
* conditions and the following disclaimer in the documentation and/or other
* materials provided with the distribution.
*
* 3. Neither the name of Nordic Semiconductor ASA nor the names of its
* contributors may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* 4. This software, with or without modification, must only be used with a
* Nordic Semiconductor ASA integrated circuit.
*
* 5. Any software provided in binary form under this license must not be reverse
* engineered, decompiled, modified and/or disassembled.
*
* THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
* OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
* GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*/
/** @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 "nrf_drv_ppi.h"
#include "nrf_drv_timer.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 1000
#define TOTAL_BUFFER_EVENT_COUNT 100 //100 000
volatile uint8_t state = 1;
static const nrf_drv_timer_t m_timer = NRF_DRV_TIMER_INSTANCE(0);
static nrf_saadc_value_t m_buffer_pool[2][SAMPLES_IN_BUFFER];
static nrf_ppi_channel_t m_ppi_channel;
static uint32_t m_adc_evt_counter;
void timer_handler(nrf_timer_event_t event_type, void * p_context)
{
}
void saadc_sampling_event_init(void)
{
ret_code_t err_code;
err_code = nrf_drv_ppi_init();
APP_ERROR_CHECK(err_code);
nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
timer_cfg.bit_width = NRF_TIMER_BIT_WIDTH_32;
err_code = nrf_drv_timer_init(&m_timer, &timer_cfg, timer_handler);
APP_ERROR_CHECK(err_code);
/* setup m_timer for compare event every 400ms */
uint32_t ticks = nrf_drv_timer_us_to_ticks(&m_timer, 10); // Trigger sample task every 10 us
nrf_drv_timer_extended_compare(&m_timer,
NRF_TIMER_CC_CHANNEL0,
ticks,
NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
false);
nrf_drv_timer_enable(&m_timer);
uint32_t timer_compare_event_addr = nrf_drv_timer_compare_event_address_get(&m_timer,
NRF_TIMER_CC_CHANNEL0);
uint32_t saadc_sample_task_addr = nrf_drv_saadc_sample_task_get();
/* setup ppi channel so that timer compare event is triggering sample task in SAADC */
err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel);
APP_ERROR_CHECK(err_code);
err_code = nrf_drv_ppi_channel_assign(m_ppi_channel,
timer_compare_event_addr,
saadc_sample_task_addr);
APP_ERROR_CHECK(err_code);
}
void saadc_sampling_event_enable(void)
{
ret_code_t err_code = nrf_drv_ppi_channel_enable(m_ppi_channel);
APP_ERROR_CHECK(err_code);
}
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);
int i;
NRF_LOG_INFO("ADC event number: %d", (int)m_adc_evt_counter);
// for (i = 0; i < SAMPLES_IN_BUFFER; i++)
// {
// NRF_LOG_INFO("%d", p_event->data.done.p_buffer[i]);
// }
m_adc_evt_counter++;
}
if(m_adc_evt_counter == TOTAL_BUFFER_EVENT_COUNT)
{
nrf_drv_ppi_channel_disable(m_ppi_channel); // Disable events from TIMER to trigger SAADC SAMPLE
nrf_drv_timer_disable(&m_timer); // Stop timer
}
}
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);
channel_config.acq_time = NRF_SAADC_ACQTIME_5US;
err_code = nrf_drv_saadc_init(NULL, saadc_callback);
APP_ERROR_CHECK(err_code);
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);
}
/**
* @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();
saadc_sampling_event_init();
saadc_sampling_event_enable();
NRF_LOG_INFO("SAADC HAL simple example started.");
while (1)
{
nrf_pwr_mgmt_run();
NRF_LOG_FLUSH();
}
}
/** @} */
Best regards,
Jørgen
Thank you for the code. It works.
I found that if one connects A0 input to VDD on the board the values in the first buffer is much lower than in the subsequent buffers.
It does not happened if I connect ADC input to VDD internally, i.e. replace NRF_SAADC_INPUT_AIN0 with NRF_SAADC_INPUT_VDD.
Here is my modifications:
for (i = 0; i < 2; i++)
{
NRF_LOG_INFO("%d", p_event->data.done.p_buffer[i]);
}
and here is prinout when usnig NRF_SAADC_INPUT_AIN0 :
<info> app: SAADC HAL simple example started.
<info> app: ADC event number: 0
<info> app: 35
<info> app: 39
<info> app: ADC event number: 1
<info> app: 169
<info> app: 169
<info> app: ADC event number: 2
<info> app: 171
<info> app: 167
<info> app: ADC event number: 3
Can you explain this?
Thanks,
Mike
I'm not sure exactly what is causing this, but it could be related to charging of the internal capacitor when the input is floating. When the pin has not been sampled for a while, it may take longer for the capacitor to be changed than it does for the subsequent samplings that are performed almost back-to-back. Note that this is purely speculations, there could be other reasons for this as well. As long as you are not planning to sample floating inputs, and the first sample does not show this behavior when the inputs are connected, I do not see this as an issue.