PPI CHANNEL USED TO generate pulse wave

[Fab1223]

Hi All,

I am using NRF51822 chip pca10001 development board.

I flashed ble_app_hrs application to the board.

I configure 3 channel for PPI.

static void ppi_init(void)
{
  
  uint32_t err_code;

	 err_code = sd_ppi_channel_assign(0,
                                     &(NRF_TIMER2->EVENTS_COMPARE[0]),
                                     &(NRF_GPIOTE->TASKS_OUT[0]));
    APP_ERROR_CHECK(err_code);
	
		
		err_code = sd_ppi_channel_assign(1,
                                     &(NRF_TIMER2->EVENTS_COMPARE[1]),
                                     &(NRF_GPIOTE->TASKS_OUT[0]));
    APP_ERROR_CHECK(err_code);
	
		err_code = sd_ppi_channel_assign(2,
                                     &(NRF_TIMER2->EVENTS_COMPARE[1]),
                                     &(NRF_TIMER2->TASKS_CLEAR));
    APP_ERROR_CHECK(err_code);
}

I configure gpiote task for channel 0.

void gpiote_channel_0_set(void)
{
	 nrf_gpiote_task_config(0, AC_OUT_PIN, NRF_GPIOTE_POLARITY_TOGGLE, \
                           NRF_GPIOTE_INITIAL_VALUE_HIGH);
}

Now i enable all 3 channels.

__inline void ppi_enable(void)
{
		uint32_t err_code;
		err_code = sd_ppi_channel_enable_set( (PPI_CHEN_CH0_Msk) |  (PPI_CHEN_CH1_Msk)| (PPI_CHEN_CH2_Msk));
    APP_ERROR_CHECK(err_code)
}

The timer2 is intialised as fallows.

static void timer2_init(void)
{
		
   /* Start 16 MHz crystal oscillator */
    NRF_CLOCK->EVENTS_HFCLKSTARTED    = 0;
    NRF_CLOCK->TASKS_HFCLKSTART       = 1;
    /* Wait for the external oscillator to start up */
    while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0)       
    {
        // Do nothing.
    }
		NRF_TIMER2->TASKS_CLEAR = 1;
    NRF_TIMER2->MODE        = TIMER_MODE_MODE_Timer;
		NRF_TIMER2->PRESCALER   = 4;

    /* Load initial values to Timer 2 CC registers */
    /* Set initial CC0 value to anything > 1 */
		NRF_TIMER2->BITMODE   = TIMER_BITMODE_BITMODE_16Bit;
	
}

Now i am updating timer2 cc0 value and cc1 value from BLE characteristic interrupt and then i start the timer.

But for constant cc0 and cc1 value its giving two waveform.

ex- cc0=1000(1ms), cc1=10000(9ms);

i am getting two wave

1. 1ms on and 9ms off.

2. 1ms off and 9ms on.

I need to get only first wave all the time if i write constant value to ble characteristic

Could any one tell me how to solve this?. ( I need to do this with PPI only).

I tried by reinitialising all ppi and gpiote for every ble characteristic interrupt then also it dont work.

Kindly tell me what is the issue.

Regards Punit

[Susheel Nuguru]

can you try not using sd_ppi function and enable ppi directly using PPI registers. If it works then something is wrong in softdevice. I am sorry for my late response, i am on vacation and wont be back to work until Monday.

[Susheel Nuguru]

on nRF51, we were struggling a lot with it. In PWM missing one interrupt that toggles the pin would mean that the signal is inverted. This could happen with BLE events as they are running on higher priority. The link i sent you today the engineer tried his best to have a workaround with this to have a stable PWM output even in this cases. with nRF52 we do not have this problem.

When you try to update the duty cycle, in GPIOTE interrupt handler if a TOGGLE is missed due to long BLE event that blocked it, it will invert the signal. In nRF52 there are seperate set and clear tasks that are used instead of toggle and even if we miss one set and clear then only one pusle is inverted and the rest will be ok