nrf52_sdk_ppi_example.c

/**
 * Copyright (c) 2014 - 2021, Nordic Semiconductor ASA
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 *
 * 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
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 *    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.
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 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
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/** @file
*
* @defgroup ppi_example_main main.c
* @{
* @ingroup ppi_example
* @brief PPI Example Application main file.
*
* This file contains the source code for a sample application using PPI to communicate between timers.
*
*/
#include <stdint.h>

#include "nrf_delay.h"
#include "app_error.h"

#include "nrf_drv_ppi.h"
#include "nrf_drv_timer.h"

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

#define PPI_EXAMPLE_TIMERS_PHASE_SHIFT_DELAY    (10)    // 1s = 10 * 100ms (Timer 0 interrupt)
#define PPI_EXAMPLE_TIMER0_INTERVAL             (100)   // Timer interval in milliseconds
#define PPI_EXAMPLE_TIMER1_INTERVAL             (2000)  // Timer interval in milliseconds
#define PPI_EXAMPLE_TIMER2_INTERVAL             (2000)  // Timer interval in milliseconds


static const nrf_drv_timer_t m_timer0 = NRF_DRV_TIMER_INSTANCE(0);
static const nrf_drv_timer_t m_timer1 = NRF_DRV_TIMER_INSTANCE(1);
static const nrf_drv_timer_t m_timer2 = NRF_DRV_TIMER_INSTANCE(2);

static nrf_ppi_channel_t m_ppi_channel1;
static nrf_ppi_channel_t m_ppi_channel2;

static volatile uint32_t m_counter;

static void timer0_event_handler(nrf_timer_event_t event_type, void * p_context)
{
    ++m_counter;
}

/* Timer event handler. Not used since Timer1 and Timer2 are used only for PPI. */
static void empty_timer_handler(nrf_timer_event_t event_type, void * p_context)
{
}


/** @brief Function for initializing the PPI peripheral.
*/
static void ppi_init(void)
{
    uint32_t err_code = NRF_SUCCESS;

    err_code = nrf_drv_ppi_init();
    APP_ERROR_CHECK(err_code);

    /* Configure 1st available PPI channel to stop TIMER0 counter on TIMER1 COMPARE[0] match,
     * which is every even number of seconds.
     */
    err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel1);
    APP_ERROR_CHECK(err_code);
    err_code = nrf_drv_ppi_channel_assign(m_ppi_channel1,
                                          nrf_drv_timer_event_address_get(&m_timer1,
                                                                          NRF_TIMER_EVENT_COMPARE0),
                                          nrf_drv_timer_task_address_get(&m_timer0,
                                                                         NRF_TIMER_TASK_STOP));
    APP_ERROR_CHECK(err_code);

    /* Configure 2nd available PPI channel to start TIMER0 counter at TIMER2 COMPARE[0] match,
     * which is every odd number of seconds.
     */
    err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel2);
    APP_ERROR_CHECK(err_code);
    err_code = nrf_drv_ppi_channel_assign(m_ppi_channel2,
                                          nrf_drv_timer_event_address_get(&m_timer2,
                                                                          NRF_TIMER_EVENT_COMPARE0),
                                          nrf_drv_timer_task_address_get(&m_timer0,
                                                                         NRF_TIMER_TASK_START));
    APP_ERROR_CHECK(err_code);

    // Enable both configured PPI channels
    err_code = nrf_drv_ppi_channel_enable(m_ppi_channel1);
    APP_ERROR_CHECK(err_code);
    err_code = nrf_drv_ppi_channel_enable(m_ppi_channel2);
    APP_ERROR_CHECK(err_code);
}


/** @brief Function for Timer 0 initialization.
 *  @details Timer 0 will be stopped and started by Timer 1 and Timer 2 respectively using PPI.
 *           It is configured to generate an interrupt every 100ms.
 */
static void timer0_init(void)
{
    // Check TIMER0 configuration for details.
    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    timer_cfg.frequency = NRF_TIMER_FREQ_31250Hz;
    ret_code_t err_code = nrf_drv_timer_init(&m_timer0, &timer_cfg, timer0_event_handler);
    APP_ERROR_CHECK(err_code);

    nrf_drv_timer_extended_compare(&m_timer0,
                                   NRF_TIMER_CC_CHANNEL0,
                                   nrf_drv_timer_ms_to_ticks(&m_timer0,
                                                             PPI_EXAMPLE_TIMER0_INTERVAL),
                                   NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
                                   true);
}

/** @brief Function for Timer 1 initialization.
 *  @details Initializes TIMER1 peripheral to generate an event every 2 seconds. The events are
 *           generated at even numbers of seconds after starting the example (2, 4, 6 ...) and they
 *           are used to stop TIMER0 via PPI: TIMER1->EVENT_COMPARE[0] triggers TIMER0->TASK_STOP.
 */
static void timer1_init(void)
{
    // Check TIMER1 configuration for details.
    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    timer_cfg.frequency = NRF_TIMER_FREQ_31250Hz;
    ret_code_t err_code = nrf_drv_timer_init(&m_timer1, &timer_cfg, empty_timer_handler);
    APP_ERROR_CHECK(err_code);

    nrf_drv_timer_extended_compare(&m_timer1,
                                   NRF_TIMER_CC_CHANNEL0,
                                   nrf_drv_timer_ms_to_ticks(&m_timer1,
                                                             PPI_EXAMPLE_TIMER1_INTERVAL),
                                   NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
                                   false);
}


/** @brief Function for Timer 2 initialization.
 *  @details Initializes TIMER2 peripheral to generate an event every 2 seconds. The events are
 *           generated at odd numbers of seconds after starting the example (3, 5, 7 ...) and they
 *           are used to start TIMER0 via PPI: TIMER2->EVENT_COMPARE[0] triggers TIMER0->TASK_START.
 */
static void timer2_init(void)
{
    // Check TIMER2 configuration for details.
    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    timer_cfg.frequency = NRF_TIMER_FREQ_31250Hz;
    ret_code_t err_code = nrf_drv_timer_init(&m_timer2, &timer_cfg, empty_timer_handler);
    APP_ERROR_CHECK(err_code);

    nrf_drv_timer_extended_compare(&m_timer2,
                                   NRF_TIMER_CC_CHANNEL0,
                                   nrf_drv_timer_ms_to_ticks(&m_timer2,
                                                             PPI_EXAMPLE_TIMER2_INTERVAL),
                                   NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
                                   false);
}

/**
 * @brief Function for application main entry.
 */
int main(void)
{
    uint32_t old_val = 0;
    uint32_t err_code;

    err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();

    ppi_init();
    timer0_init(); // Timer used to increase m_counter every 100ms.
    timer1_init(); // Timer to generate events on even number of seconds - stopping Timer 0
    timer2_init(); // Timer to generate events on odd number of seconds - starting Timer 0

    NRF_LOG_INFO("PPI example started.");

    // Start clock.
    nrf_drv_timer_enable(&m_timer0);

    /* Below delay is implemented to ensure that Timer0 interrupt will execute before PPI action.
     * Please be aware that such solution was tested only in this simple example code. In case
     * of more complex systems with higher level interrupts this may lead to not correct timers
     * synchronization.
     */
    nrf_delay_us(5);
    nrf_drv_timer_enable(&m_timer1);

    m_counter = (uint32_t)-PPI_EXAMPLE_TIMERS_PHASE_SHIFT_DELAY;

    // Timer 2 will start one second after Timer 1 (m_counter will equal 0 after 1s)
    while (m_counter != 0) 
    {
        // just wait
    }
    nrf_drv_timer_enable(&m_timer2);

    while (true)
    {
        uint32_t counter = m_counter;
        if (old_val != counter)
        {
            old_val = counter;

            NRF_LOG_INFO("Current count: %u", counter);
            NRF_LOG_FLUSH();
        }
    }
}

/** @} */