Transfer data through BLE problem

Question

Hi all,

I am using nRF52832 with SDK 13.0.0. And I use the ble_perpheral -> ble_app_uart example.

I am trying to send data through BLE and. I'm using timer 2 to sampling SAADC data with sampling frequency is 500Hz. In timer 2 interrupt function, I have 2 event compare to do my work.

I get 6 byte each time sampling and I wait for in enough 60 byte and then send data through BLE by ble_nus_string_send function that mean every 20ms I send the data one time, like this code below:

void TIMER2_IRQHandler(void)
{
if ((NRF_TIMER2->EVENTS_COMPARE[0] != 0) && ((NRF_TIMER2->INTENSET & TIMER_INTENSET_COMPARE0_Msk) != 0))
  {
		nrf_gpio_pin_write(19, 1);
		nrf_gpio_pin_write(18, 0);
		NRF_TIMER2->EVENTS_COMPARE[0] = 0;           //Clear compare register 0 event		
		saadc_start();
		while(!NRF_SAADC->EVENTS_END){}
		NRF_SAADC->EVENTS_END = 0;
		if(((uint16_t)data_buffer)>>15)
		{
			data_buffer=data_buffer&0xffff0000;
		}
		if(data_buffer>>31)
		{
			data_buffer=data_buffer&0x0000ffff;
		}
		
		saadc_UartSend[count] = data_buffer&0x3f;
    count++;
		saadc_UartSend[count] = ((data_buffer >> 6UL)&0x3f)|0x40;
    count++;
		saadc_UartSend[count] = ((data_buffer >> 16UL)&0x3f)|0x80;
    count++;
		saadc_UartSend[count] = ((data_buffer >> 22UL)&0x3f)|0xc0;
    count++;
 }
	
		if ((NRF_TIMER2->EVENTS_COMPARE[1] != 0) && ((NRF_TIMER2->INTENSET & TIMER_INTENSET_COMPARE1_Msk) != 0))
		{
			
			NRF_TIMER2->EVENTS_COMPARE[1] = 0;           //Clear compare register 1 event
			saadc_start();
			while(!NRF_SAADC->EVENTS_END){}
			NRF_SAADC->EVENTS_END = 0;         
      if(((uint16_t)data_buffer)>>15)
		   {
			   data_buffer=data_buffer&0xffff0000;
		   }
		  if(data_buffer>>31)
		   {
			   data_buffer=data_buffer&0x0000ffff;
		   }				// clear EVENTS_END
			 
		 saadc_UartSend[count] = ((data_buffer>> 16UL)&0x3f)|0x80;  // divide and add index bit 
     count++;
		 saadc_UartSend[count]= ((data_buffer>> 22UL)&0x3f)|0xc0;  
     count++;
		 uint32_t err_code;
			if(count==60) 
				{
				  do
               {
                    err_code = ble_nus_string_send(&m_nus, saadc_UartSend, 60);
                    if ( (err_code != NRF_ERROR_INVALID_STATE) && (err_code != NRF_ERROR_BUSY) )
                    {
                        APP_ERROR_CHECK(err_code);
                    }
                } while (err_code == NRF_ERROR_BUSY);
          count=0;
					}
			nrf_gpio_pin_write(19, 0);
			nrf_gpio_pin_write(18, 1);

			 }
     
}

The timer_init() function is like this:

void timer_init()
{
	NRF_TIMER2->MODE = TIMER_MODE_MODE_Timer;  // Set the timer in Counter Mode // 0x4000A000
  NRF_TIMER2->TASKS_CLEAR = 1;               // clear the task first to be usable for later
	NRF_TIMER2->PRESCALER = 7;                             //Set prescaler. Higher number gives slower timer. Prescaler = 0 gives 16MHz timer
	NRF_TIMER2->BITMODE = TIMER_BITMODE_BITMODE_08Bit;		 //Set counter to 16 bit resolution
	NRF_TIMER2->CC[0] = 0;                             //Set value for TIMER2 compare register 0
	NRF_TIMER2->CC[1] = 60;                                 //Set value for TIMER2 compare register 1

	NRF_TIMER2->INTENSET = (TIMER_INTENSET_COMPARE0_Enabled << TIMER_INTENSET_COMPARE0_Pos)|(TIMER_INTENSET_COMPARE1_Enabled << TIMER_INTENSET_COMPARE1_Pos);
  NVIC_SetPriority(TIMER2_IRQn, 6);
	NVIC_EnableIRQ(TIMER2_IRQn);
	NRF_TIMER2->TASKS_START = 1;  	
}

And in saadc_init() function I setup SAADC in scan_mode:

void saadc_init(void)
{

		
		NRF_SAADC->RESOLUTION = 2; // 12 BIT MODE
		NRF_SAADC->OVERSAMPLE = 0; //bypass oversample
		
		
		NRF_SAADC->CH[0].CONFIG = 0x0 << 0UL | 0x0 << 4UL | 0x0 << 8UL | 0x0 << 12UL | 0x2 << 16UL;
		NRF_SAADC->CH[0].PSELP = 1; // NRF_SAADC_INPUT_AIN0
		NRF_SAADC->CH[0].PSELN = 0; // NRF_SAADC_INPUT_DISABLED
		
		NRF_SAADC->CH[1].CONFIG = 0x0 << 0UL | 0x0 << 4UL | 0x0 << 8UL | 0x0 << 12UL | 0x2 << 16UL;
		NRF_SAADC->CH[1].PSELP = 2; // NRF_SAADC_INPUT_AIN0
		NRF_SAADC->CH[1].PSELN = 0; // NRF_SAADC_INPUT_DISABLED
		

	
		NRF_SAADC->INTEN = 0x00000;

		NRF_SAADC->RESULT.PTR = (uint32_t)(&data_buffer);
		NRF_SAADC->RESULT.MAXCNT = 2; // number of samples


}

when I test with nRF52 Connect app. It can read the data is received in log file like. According to the time line show in log file, it seem like I got the data every 20ms without problem.

But when i try with nRF ToolBox UART the app is pathetic lag and then stopped working and I don't know why? My connection interval equal 7.5ms

Can anyone advise on how this problem can be solved?

Thanks in advance!