Hi Sir
I am using an example from NCS 2.6.0 and want to modify it to use ADC channel 6 (P0.30) to read voltage values, but I am unable to get the correct values. (When I flash the example using ADC channel 0, it reads the values correctly.) How should I modify it? Also, I want to continuously read the values rather than reading just once as in the example. Could you provide me with suggestions?
I am using the nRF52840 DK board to verify the ADC readings.
C:\ncs\v2.6.0\modules\hal\nordic\nrfx\samples\src\nrfx_saadc\maximum_performance
==================================================================================================
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#include <nrfx_example.h>
#include <saadc_examples_common.h>
#include <nrfx_saadc.h>
#include <helpers/nrfx_gppi.h>
#include <nrfx_timer.h>
#include <nrfx_gpiote.h>
#define NRFX_LOG_MODULE EXAMPLE
#define NRFX_EXAMPLE_CONFIG_LOG_ENABLED 1
#define NRFX_EXAMPLE_CONFIG_LOG_LEVEL 3
#include <nrfx_log.h>
/**
* @defgroup nrfx_saadc_maximum_performance_example Maximum performance SAADC example
* @{
* @ingroup nrfx_saadc_examples
*
* @brief Example showing advanced functionality of nrfx_saadc driver operating at its peak performance.
*
* @details Application initializes nrfx_saadc driver and starts operating in the non-blocking mode. Sampling is
* performed at the highest supported frequency.
* In the example, @ref m_single_channel is configured and the SAADC driver is set to the advanced mode.
* To achieve maximum performance:
* - Performing sampling at @ref MAX_SAADC_SAMPLE_FREQUENCY requires an external timer. It is done
* by setting up endpoints of the channel @ref m_gppi_channels [ @p gppi_channels_purpose_t::SAADC_SAMPLING ]
* to trigger SAADC sample task ( @p nrf_saadc_task_t::NRF_SAADC_TASK_SAMPLE ) on the timer compare event.
* - Hardware start-on-end must be provided. It is done by setting up endpoints of the channel
* @ref m_gppi_channels [ @p gppi_channels_purpose_t::SAADC_START_ON_END ] to trigger SAADC task start
* ( @p nrf_saadc_task_t::NRF_SAADC_TASK_START ) on the SAADC event end ( @p nrf_saadc_event_t::NRF_SAADC_EVENT_END ).
*
* Calibration in a non-blocking manner is triggered by @p nrfx_saadc_offset_calibrate. Then at @p NRFX_SAADC_EVT_CALIBRATEDONE
* event in @ref saadc_handler() sampling is initiated by calling @p nrfx_saadc_mode_trigger() function.
* Consecutive sample tasks are triggered by the external timer at the sample rate specified in @ref SAADC_SAMPLE_FREQUENCY symbol.
*
* In the example there is GPPI channel configured to test the functionality of SAADC. The endpoints are setup up in a way
* that @p NRF_SAADC_EVENT_RESULTDONE event is connected with the GPIOTE task that toggles the @ref OUT_GPIO_PIN pin.
*/
/** @brief Symbol specifying timer instance to be used. */
#define TIMER_INST_IDX 0
/** @brief Symbol specifying GPIOTE instance to be used. */
#define GPIOTE_INST_IDX 0
/** @brief Symbol specifying analog input to be observed by SAADC channel 0. */
//#define CH0_AIN ANALOG_INPUT_TO_SAADC_AIN(ANALOG_INPUT_A0)
#define CH0_AIN ANALOG_INPUT_TO_SAADC_AIN(30)
/** @brief Symbol specifying GPIO pin used to test the functionality of SAADC. */
#define OUT_GPIO_PIN LOOPBACK_PIN_1B
/** @brief Acquisition time [us] for source resistance <= 10 kOhm (see SAADC electrical specification). */
#define ACQ_TIME_10K 3UL
/** @brief Conversion time [us] (see SAADC electrical specification). */
#define CONV_TIME 2UL
/** @brief Symbol specifying maximal possible SAADC sample rate (see SAADC electrical specification). */
#define MAX_SAADC_SAMPLE_FREQUENCY 200000UL
/** @brief Symbol specifying SAADC sample frequency for the continuous sampling. */
#define SAADC_SAMPLE_FREQUENCY MAX_SAADC_SAMPLE_FREQUENCY
/** @brief Symbol specifying time in microseconds to wait for timer handler execution. */
#define TIME_TO_WAIT_US (uint32_t)(1000000UL / SAADC_SAMPLE_FREQUENCY)
/**
* @brief Symbol specifying the number of sample buffers ( @ref m_sample_buffers ).
* Two buffers are required for performing double-buffered conversions.
*/
#define BUFFER_COUNT 2UL
/** @brief Symbol specifying the size of singular sample buffer ( @ref m_sample_buffers ). */
#define BUFFER_SIZE 2UL
/** @brief Symbol specifying the number of SAADC samplings to trigger. */
#define SAMPLING_ITERATIONS 3UL
/** @brief Symbol specifying the resolution of the SAADC. */
#define RESOLUTION NRF_SAADC_RESOLUTION_10BIT
/** @brief SAADC channel configuration structure for single channel use. */
static const nrfx_saadc_channel_t m_single_channel = SAADC_CHANNEL_SE_ACQ_3US(CH0_AIN, 0);
/** @brief Samples buffer to store values from a SAADC channel. */
#if (NRF_SAADC_8BIT_SAMPLE_WIDTH == 8) && (RESOLUTION == NRF_SAADC_RESOLUTION_8BIT)
static uint8_t m_sample_buffers[BUFFER_COUNT][BUFFER_SIZE];
#else
static uint16_t m_sample_buffers[BUFFER_COUNT][BUFFER_SIZE];
#endif
/** @brief Array of the GPPI channels. */
static uint8_t m_gppi_channels[2];
/** @brief Enum with intended uses of GPPI channels defined as @ref m_gppi_channels. */
typedef enum
{
SAADC_SAMPLING, ///< Triggers SAADC sampling task on external timer event.
SAADC_START_ON_END, ///< Triggers SAADC start task on SAADC end event.
} gppi_channels_purpose_t;
/** Maximum sampling rate of SAADC is 200 [kHz]. */
NRFX_STATIC_ASSERT(SAADC_SAMPLE_FREQUENCY <= (MAX_SAADC_SAMPLE_FREQUENCY));
/** For continuous sampling the sample rate SAADC_SAMPLE_FREQUENCY should fulfill the following criteria (see SAADC Continuous sampling). */
NRFX_STATIC_ASSERT(SAADC_SAMPLE_FREQUENCY <= (1000000UL / (ACQ_TIME_10K + CONV_TIME)));
/**
* @brief Function for handling SAADC driver events.
*
* @param[in] p_event Pointer to an SAADC driver event.
*/
static void saadc_handler(nrfx_saadc_evt_t const * p_event)
{
nrfx_err_t status;
(void)status;
static uint16_t buffer_index = 1;
static uint16_t buf_req_evt_counter;
uint16_t samples_number;
switch(p_event->type)
{
case NRFX_SAADC_EVT_CALIBRATEDONE:
NRFX_LOG_INFO("SAADC event: CALIBRATEDONE");
status = nrfx_saadc_mode_trigger();
NRFX_ASSERT(status == NRFX_SUCCESS);
break;
case NRFX_SAADC_EVT_READY:
NRFX_LOG_INFO("SAADC event: READY");
nrfx_gppi_channels_enable(NRFX_BIT(m_gppi_channels[SAADC_SAMPLING]));
break;
case NRFX_SAADC_EVT_BUF_REQ:
NRFX_LOG_INFO("SAADC event: BUF_REQ");
if (++buf_req_evt_counter < SAMPLING_ITERATIONS)
{
/* Next available buffer must be set on the NRFX_SAADC_EVT_BUF_REQ event to achieve the continuous conversion. */
status = nrfx_saadc_buffer_set(m_sample_buffers[buffer_index++], BUFFER_SIZE);
NRFX_ASSERT(status == NRFX_SUCCESS);
buffer_index = buffer_index % BUFFER_COUNT;
}
else
{
nrfx_gppi_channels_disable(NRFX_BIT(m_gppi_channels[SAADC_START_ON_END]));
}
break;
case NRFX_SAADC_EVT_DONE:
NRFX_LOG_INFO("SAADC event: DONE");
NRFX_LOG_INFO("Sample buffer address == %p", p_event->data.done.p_buffer);
samples_number = p_event->data.done.size;
for (uint16_t i = 0; i < samples_number; i++)
{
NRFX_LOG_INFO("[Sample %u] value == %d",
i, NRFX_SAADC_SAMPLE_GET(RESOLUTION, p_event->data.done.p_buffer, i));
}
break;
case NRFX_SAADC_EVT_FINISHED:
NRFX_LOG_INFO("FINISHED");
nrfx_gppi_channels_disable(NRFX_BIT(m_gppi_channels[SAADC_SAMPLING]));
break;
default:
break;
}
}
/**
* @brief Function for handling TIMER driver events.
*
* @param[in] event_type Timer event.
* @param[in] p_context General purpose parameter set during initialization of the timer.
* This parameter can be used to pass additional information to the handler
* function for example the timer ID.
*/
static void timer_handler(nrf_timer_event_t event_type, void * p_context)
{
(void)event_type;
(void)p_context;
}
/**
* @brief Function for application main entry.
*
* @return Nothing.
*/
int main(void)
{
nrfx_err_t status;
(void)status;
#if defined(__ZEPHYR__)
IRQ_CONNECT(NRFX_IRQ_NUMBER_GET(NRF_SAADC), IRQ_PRIO_LOWEST, nrfx_saadc_irq_handler, 0, 0);
IRQ_CONNECT(NRFX_IRQ_NUMBER_GET(NRF_GPIOTE_INST_GET(GPIOTE_INST_IDX)), IRQ_PRIO_LOWEST,
NRFX_GPIOTE_INST_HANDLER_GET(GPIOTE_INST_IDX), 0, 0);
#endif
NRFX_EXAMPLE_LOG_INIT();
NRFX_LOG_INFO("Starting nrfx_saadc maximum performance example.");
NRFX_EXAMPLE_LOG_PROCESS();
status = nrfx_saadc_init(NRFX_SAADC_DEFAULT_CONFIG_IRQ_PRIORITY);
NRFX_ASSERT(status == NRFX_SUCCESS);
nrfx_timer_t timer_inst = NRFX_TIMER_INSTANCE(TIMER_INST_IDX);
uint32_t base_frequency = NRF_TIMER_BASE_FREQUENCY_GET(timer_inst.p_reg);
nrfx_timer_config_t timer_config = NRFX_TIMER_DEFAULT_CONFIG(base_frequency);
timer_config.bit_width = NRF_TIMER_BIT_WIDTH_32;
timer_config.p_context = &timer_inst;
status = nrfx_timer_init(&timer_inst, &timer_config, timer_handler);
NRFX_ASSERT(status == NRFX_SUCCESS);
nrfx_timer_clear(&timer_inst);
/* Creating variable desired_ticks to store the output of nrfx_timer_us_to_ticks function. */
uint32_t desired_ticks = nrfx_timer_us_to_ticks(&timer_inst, TIME_TO_WAIT_US);
/*
* Setting the timer channel NRF_TIMER_CC_CHANNEL0 in the extended compare mode to clear
* the timer and to not trigger an interrupt if the internal counter register is equal to
* desired_ticks.
*/
nrfx_timer_extended_compare(&timer_inst,
NRF_TIMER_CC_CHANNEL0,
desired_ticks,
NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
false);
status = nrfx_saadc_channel_config(&m_single_channel);
NRFX_ASSERT(status == NRFX_SUCCESS);
/*
* Setting the advanced configuration with triggering sampling by the internal timer disabled
* (internal_timer_cc = 0) and without software start task on end event (start_on_end = false).
*/
nrfx_saadc_adv_config_t adv_config = NRFX_SAADC_DEFAULT_ADV_CONFIG;
adv_config.internal_timer_cc = 0;
adv_config.start_on_end = false;
uint32_t channel_mask = nrfx_saadc_channels_configured_get();
status = nrfx_saadc_advanced_mode_set(channel_mask,
RESOLUTION,
&adv_config,
saadc_handler);
NRFX_ASSERT(status == NRFX_SUCCESS);
status = nrfx_saadc_buffer_set(m_sample_buffers[0], BUFFER_SIZE);
NRFX_ASSERT(status == NRFX_SUCCESS);
/*
* Allocate a dedicated channel and configure endpoints of that channel so that the timer compare event
* is connected with the SAADC sample task. This means that each time the timer interrupt occurs,
* the SAADC sampling will be triggered.
*/
status = nrfx_gppi_channel_alloc(&m_gppi_channels[SAADC_SAMPLING]);
NRFX_ASSERT(status == NRFX_SUCCESS);
nrfx_gppi_channel_endpoints_setup(m_gppi_channels[SAADC_SAMPLING],
nrfx_timer_compare_event_address_get(&timer_inst, NRF_TIMER_CC_CHANNEL0),
nrf_saadc_task_address_get(NRF_SAADC, NRF_SAADC_TASK_SAMPLE));
/*
* Allocate a dedicated channel and configure endpoints of that so that the SAADC event end is connected
* with the SAADC task start. This means that each time the SAADC fills up the result buffer,
* the SAADC will be restarted and the result buffer will be prepared in RAM.
*/
status = nrfx_gppi_channel_alloc(&m_gppi_channels[SAADC_START_ON_END]);
NRFX_ASSERT(status == NRFX_SUCCESS);
nrfx_gppi_channel_endpoints_setup(m_gppi_channels[SAADC_START_ON_END],
nrf_saadc_event_address_get(NRF_SAADC, NRF_SAADC_EVENT_END),
nrf_saadc_task_address_get(NRF_SAADC, NRF_SAADC_TASK_START));
nrfx_gpiote_t const gpiote_inst = NRFX_GPIOTE_INSTANCE(GPIOTE_INST_IDX);
status = nrfx_gpiote_init(&gpiote_inst, NRFX_GPIOTE_DEFAULT_CONFIG_IRQ_PRIORITY);
NRFX_ASSERT(status == NRFX_SUCCESS);
NRFX_LOG_INFO("GPIOTE status: %s",
nrfx_gpiote_init_check(&gpiote_inst) ? "initialized" : "not initialized");
pin_on_event_toggle_setup(&gpiote_inst, OUT_GPIO_PIN,//
nrf_saadc_event_address_get(NRF_SAADC, NRF_SAADC_EVENT_RESULTDONE));
nrfx_timer_enable(&timer_inst);
nrfx_gppi_channels_enable(NRFX_BIT(m_gppi_channels[SAADC_START_ON_END]));
status = nrfx_saadc_offset_calibrate(saadc_handler);
NRFX_ASSERT(status == NRFX_SUCCESS);
while (1)
{
NRFX_EXAMPLE_LOG_PROCESS();
}
}
/** @} */
