Question about strange behavior of Timer0

[JiachengWang]

I want to use timer0 to get exact time delay (without soft device used).

Timer0 configuration is as

void timer0_initialization(void)
{
  NRF_TIMER0->MODE = TIMER_MODE_MODE_Timer;
  NRF_TIMER0->PRESCALER = 0;
  NRF_TIMER0->BITMODE = TIMER_BITMODE_BITMODE_32Bit;
  NRF_TIMER0->SHORTS = TIMER_SHORTS_COMPARE0_CLEAR_Enabled << TIMER_SHORTS_COMPARE0_CLEAR_Pos;
  NRF_TIMER0->INTENSET = TIMER_INTENSET_COMPARE0_Enabled << TIMER_INTENSET_COMPARE0_Pos;
  NRF_TIMER0->TASKS_STOP = 1;
}

the test main function is as

int main(void)
{
  uint32_t i;
  uint32_t time_capture[10];
  
 /* UART and RTC0 initialization */
  
  printf ("---------------------------------- Start ---------------------------------- \r\n");
  timer0_initialization( );      
  
  NRF_TIMER0->CC[0] = 1000 * 16;
  NRF_TIMER0->TASKS_START = 1;
        
  for (i=0; i<10; i++)
  {  
    NRF_TIMER0->EVENTS_COMPARE[0] = 0;
    time_capture[i] = NRF_RTC0->COUNTER;
    while (NRF_TIMER0->EVENTS_COMPARE[0] == 0)
    {    
       /* delay 1ms */    
    }
  }
  for (i=1; i<10; i++)
  {
    printf("i = %ld, time delay = %ld, \r\n", i, time_capture[i] - time_capture[i - 1]); 
  }
  
  while(1);
}

Since RTC0's frequency is 32K, so the output of "printf" time delay should be about 30 (1000/32.768), moreover, each time delay should be the same. However, the first time delay is much difference than others. the output of above code is like

---------------------------------- Start --------------------------------------- 
i = 1, time delay = 8, 
i = 2, time delay = 34, 
i = 3, time delay = 34, 
i = 4, time delay = 34, 
i = 5, time delay = 34, 
i = 6, time delay = 34, 
i = 7, time delay = 34, 
i = 8, time delay = 34, 
i = 9, time delay = 34, 

If add some time daly right after timer0 started like

  NRF_TIMER0->CC[0] = 1000 * 16;
  NRF_TIMER0->TASKS_START = 1;
      
/* add some time delay */
  nrf_delay_ms(10);
  
  for (i=0; i<10; i++)
  {  
    NRF_TIMER0->EVENTS_COMPARE[0] = 0;
    time_capture[i] = NRF_RTC0->COUNTER;
    while (NRF_TIMER0->EVENTS_COMPARE[0] == 0)
    {        
    }
  }

The program output is like

---------------------------------- Start --------------------------------------- 
i = 1, time delay = 0, 
i = 2, time delay = 34, 
i = 3, time delay = 34, 
i = 4, time delay = 34, 
i = 5, time delay = 34, 
i = 6, time delay = 34, 
i = 7, time delay = 34, 
i = 8, time delay = 34, 
i = 9, time delay = 34, 

The first time delay is 0, means no any time delay.

For "nrf_delay_ms(100);", "nrf_delay_ms(1000);", "nrf_delay_ms(2000);", the output are like following:

---------------------------------- Start --------------------------------------- 
i = 1, time delay = 2, 
i = 2, time delay = 34, 
i = 3, time delay = 34, 
i = 4, time delay = 34, 
i = 5, time delay = 34, 
i = 6, time delay = 34, 
i = 7, time delay = 34, 
i = 8, time delay = 34, 
i = 9, time delay = 34, 
---------------------------------- Start --------------------------------------- 
i = 1, time delay = 27, 
i = 2, time delay = 32, 
i = 3, time delay = 33, 
i = 4, time delay = 32, 
i = 5, time delay = 33, 
i = 6, time delay = 32, 
i = 7, time delay = 33, 
i = 8, time delay = 32, 
i = 9, time delay = 33, 
---------------------------------- Start --------------------------------------- 
i = 1, time delay = 21, 
i = 2, time delay = 33, 
i = 3, time delay = 32, 
i = 4, time delay = 33, 
i = 5, time delay = 32, 
i = 6, time delay = 33, 
i = 7, time delay = 32, 
i = 8, time delay = 33, 
i = 9, time delay = 32, 

It seems the first time delay is a random number. These result is obtained from nRF52832 preview DK board, the similar result is obtain with nRF51822 board.

How to understand this results of timer0? is there any bug in my code?

Thanks a lot!

[JiachengWang]

Hi, RK and Aryan,

Thanks a lot for your help.

I'm trying to re-produce the output with a "pure" SDK environment (I use a mixed environment with som function from old SDK and som my own functions before). I'm currently use UART example code in "nRF52_SDK_0.9.1_3639cc9\examples\peripheral\uart", just with a simple modification. The main function is (add timer0 config function and modify the last lines in main function):

/* Copyright (c) 2014 Nordic Semiconductor. All Rights Reserved.
 *
 * The information contained herein is property of Nordic Semiconductor ASA.
 * Terms and conditions of usage are described in detail in NORDIC
 * SEMICONDUCTOR STANDARD SOFTWARE LICENSE AGREEMENT.
 *
 * Licensees are granted free, non-transferable use of the information. NO
 * WARRANTY of ANY KIND is provided. This heading must NOT be removed from
 * the file.
 *
 */

/** @file
 * @defgroup uart_example_main main.c
 * @{
 * @ingroup uart_example
 * @brief UART Example Application main file.
 *
 * This file contains the source code for a sample application using UART.
 * 
 */

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include "app_uart.h"
#include "app_error.h"
#include "nrf_delay.h"
#include "nrf.h"
#include "bsp.h"

//#define ENABLE_LOOPBACK_TEST  /**< if defined, then this example will be a loopback test, which means that TX should be connected to RX to get data loopback. */

#define MAX_TEST_DATA_BYTES     (15U)                /**< max number of test bytes to be used for tx and rx. */
#define UART_TX_BUF_SIZE 256                         /**< UART TX buffer size. */
#define UART_RX_BUF_SIZE 1                           /**< UART RX buffer size. */

void uart_error_handle(app_uart_evt_t * p_event)
{
    if (p_event->evt_type == APP_UART_COMMUNICATION_ERROR)
    {
        APP_ERROR_HANDLER(p_event->data.error_communication);
    }
    else if (p_event->evt_type == APP_UART_FIFO_ERROR)
    {
        APP_ERROR_HANDLER(p_event->data.error_code);
    }
}



#ifdef ENABLE_LOOPBACK_TEST
/** @brief Function for setting the @ref ERROR_PIN high, and then enter an infinite loop.
 */
static void show_error(void)
{
    
    LEDS_ON(LEDS_MASK);
    while(true)
    {
        // Do nothing.
    }
}


/** @brief Function for testing UART loop back. 
 *  @details Transmitts one character at a time to check if the data received from the loopback is same as the transmitted data.
 *  @note  @ref TX_PIN_NUMBER must be connected to @ref RX_PIN_NUMBER)
 */
static void uart_loopback_test()
{
    uint8_t * tx_data = (uint8_t *)("\n\rLOOPBACK_TEST\n\r");
    uint8_t   rx_data;

    // Start sending one byte and see if you get the same
    for (uint32_t i = 0; i < MAX_TEST_DATA_BYTES; i++)
    {
        uint32_t err_code;
        while(app_uart_put(tx_data[i]) != NRF_SUCCESS);

        nrf_delay_ms(10);
        err_code = app_uart_get(&rx_data);

        if ((rx_data != tx_data[i]) || (err_code != NRF_SUCCESS))
        {
            show_error();
        }
    }
    return;
}


#endif

/********************************************************************************/
void timer0_initialization(void)
/*--------------------------------------------------------------------------------
| TIMER0 initialization
|
--------------------------------------------------------------------------------*/
{
  NRF_TIMER0->TASKS_STOP = 1;
  NRF_TIMER0->TASKS_CLEAR = 1;
  NRF_TIMER0->MODE = TIMER_MODE_MODE_Timer;
  NRF_TIMER0->PRESCALER = 0;
  NRF_TIMER0->BITMODE = TIMER_BITMODE_BITMODE_16Bit;
  NRF_TIMER0->SHORTS = TIMER_SHORTS_COMPARE0_CLEAR_Enabled << TIMER_SHORTS_COMPARE0_CLEAR_Pos;
  NRF_TIMER0->INTENSET = TIMER_INTENSET_COMPARE0_Enabled << TIMER_INTENSET_COMPARE0_Pos;
  NRF_TIMER0->TASKS_STOP = 1;
}


/**
 * @brief Function for main application entry.
 */
int main(void)
{
    LEDS_CONFIGURE(LEDS_MASK);
    LEDS_OFF(LEDS_MASK);
    uint32_t err_code;
    const app_uart_comm_params_t comm_params =
      {
          RX_PIN_NUMBER,
          TX_PIN_NUMBER,
          RTS_PIN_NUMBER,
          CTS_PIN_NUMBER,
          APP_UART_FLOW_CONTROL_ENABLED,
          false,
          UART_BAUDRATE_BAUDRATE_Baud38400
      };

    APP_UART_FIFO_INIT(&comm_params,
                         UART_RX_BUF_SIZE,
                         UART_TX_BUF_SIZE,
                         uart_error_handle,
                         APP_IRQ_PRIORITY_LOW,
                         err_code);

    APP_ERROR_CHECK(err_code);
			
/*******************************************************************************/
/*******************************************************************************/
/*******************************************************************************/
    uint32_t i;
    uint32_t time_capture[10];

    timer0_initialization( );
    
    NRF_TIMER0->CC[0] = 1 * 16; 
 
    NRF_TIMER0->TASKS_CLEAR = 1;
    NRF_TIMER0->TASKS_START = 1;
    for (i=1; i<10; i++)
    {
        while (NRF_TIMER0->EVENTS_COMPARE[0] == 0)
        {
        }  
				NRF_TIMER0->TASKS_CAPTURE[1] = 1;
        time_capture[i] = NRF_TIMER0->CC[1];
        NRF_TIMER0->EVENTS_COMPARE[0] = 0;
        (void)NRF_TIMER0->EVENTS_COMPARE[0];
    }
  
    printf("-------------------------------- Start ------------------------------- \r\n");
    for (i=0; i<10; i++)
    {
        printf("---- i = %ld, time delay = %ld\r\n", i, time_capture[i]); 
			  nrf_delay_ms(10);
    }
}
/** @} */

With smaller CC[0] value “NRF_TIMER0->CC[0] = 1 * 16” and capture timer0 counter and RTC0 is not used. The output of above code is as

-------------------------------- Start -------------------------------
---- i = 0, timer counter = 0
---- i = 1, timer counter = 7
---- i = 2, timer counter = 8
---- i = 3, timer counter = 9
---- i = 4, timer counter = 10
---- i = 5, timer counter = 11
---- i = 6, timer counter = 8
---- i = 7, timer counter = 9
---- i = 8, timer counter = 10
---- i = 9, timer counter = 11

It seems the first event still have different timer number. With some larger CC[0] value, NRF_TIMER0->CC[0] = 1000 * 16 give output

-------------------------------- Start -------------------------------
---- i = 0, timer counter = 0
---- i = 1, timer counter = 7
---- i = 2, timer counter = 5
---- i = 3, timer counter = 7
---- i = 4, timer counter = 5
---- i = 5, timer counter = 7
---- i = 6, timer counter = 5
---- i = 7, timer counter = 7
---- i = 8, timer counter = 5
---- i = 9, timer counter = 7

The code is simple, please help to check the lines of TIMER0 initialization, if some registers have wrong configured.

I'm using nRF52832 preview DK board (PCA10036), if possible, please repeat the output with above code at your side.

Thanks again and Best Regards,

Jiacheng

[JiachengWang]

sorry, it's my mistake, in timer capture loop, "i' should be started from 0, as

for (i=0; i<10; i++)
{
    while (NRF_TIMER0->EVENTS_COMPARE[0] == 0)
    {
    }  
				NRF_TIMER0->TASKS_CAPTURE[1] = 1;
    time_capture[i] = NRF_TIMER0->CC[1];
    NRF_TIMER0->EVENTS_COMPARE[0] = 0;
    (void)NRF_TIMER0->EVENTS_COMPARE[0];
}

give output

----------------------------------------------------------------
---- i = 0, timer counter = 5
---- i = 1, timer counter = 7
---- i = 2, timer counter = 5
---- i = 3, timer counter = 7
---- i = 4, timer counter = 7
---- i = 5, timer counter = 5
---- i = 6, timer counter = 7
---- i = 7, timer counter = 5
---- i = 8, timer counter = 7
---- i = 9, timer counter = 5

It seems the first event give the right timer number.

[JiachengWang]

There is a bug in my previous code.

Inside the for loop, the EVENTS_COMPARE register is cleared after the event. For MDK, since all avriable is initialized with 0, each event has the same timer number. but for GCC, the initial value is a random number (I use GCC), so the first event has a different timer number.

The correct code should be like:

time_capture[0] = NRF_RTC0->COUNTER;
NRF_TIMER0->TASKS_CLEAR = 1;
for (i=1; i<10; i++)
{
    NRF_TIMER0->EVENTS_COMPARE[0] = 0;
    (void)NRF_TIMER0->EVENTS_COMPARE[0];
    while (NRF_TIMER0->EVENTS_COMPARE[0] == 0)
    {
    }  
    time_capture[i] = NRF_RTC0->COUNTER;
}

This code will give the same timer number for each event.

[Susheel Nuguru]

i did not get it : ( now you are capturing the first RTC->COUNTER value unconditionally and still it gives you same value like others which are captured condictionally??? monday morning may be .. but i don't get it :(

[JiachengWang]

Hi, Aryan,

The first value of RTC0->COUNTER save in time_capture[0] is just used to record the initial time of waiting for the first event, and second value saved in time_capture[1] (in for loop, start form i=1) to record the time of the first event and the starting time for waiting second event, and .......

The value captured from RTC0 has no difference of unconditional/conditional, just record the time. The time used for waiting the first event is (time_capture[1] - time_capture[0]), and second event time is (time_capture[2] - time_capture[1]). The output code is

for (i=1; i<10; i++)
{
    printf("---- i = %ld, timer counter = %ld\r\n", i, time_capture[i] - time_capture[i - 1]); 
    nrf_delay_ms(100);
}

for NRF_TIMER0->CC[0] = 16 * 1000, I get the output as ---------------------------------------------------------------- ---- i = 1, timer counter = 34 ---- i = 2, timer counter = 34 ---- i = 3, timer counter = 34 ---- i = 4, timer counter = 34 ---- i = 5, timer counter = 34 ---- i = 6, timer counter = 34 ---- i = 7, timer counter = 34 ---- i = 8, timer counter = 34 ---- i = 9, timer counter = 34

Thanks a lot,

Jiacheng