How can I use 2 or more PPI channels to control 1GPIO?

RE: How can I use 2 or more PPI channels to control 1GPIO?

Austin (S.F.) — Mon, 25 May 2020 03:32:43 GMT

Hi Dmitry

You are totally right! -> "Also the timer needs some time to start up."

Thank you for your help.

Austin

RE: How can I use 2 or more PPI channels to control 1GPIO?

Dmitry — Sun, 24 May 2020 18:54:19 GMT

I couldn't get your goal.. if you need to respond to an external signal as quick as possible, you should start a timer also using PPI, but if it's a response to a software event, you cannot guarantee such a tight timings. Your code is compiled into a sequence of assembly instructions, their count depends on compiler and its settings (especially optimization level), and they cannot be executed in a zero time. Also the timer needs some time to start up.

RE: How can I use 2 or more PPI channels to control 1GPIO?

Austin (S.F.) — Sun, 24 May 2020 14:40:20 GMT

Hi Dmitry

Thanks a lot! You rescue me!

If I use "(uint32_t)&NRF_GPIOTE->TASKS_OUT[0];" , it cost timing around 1us.

I use "(uint32_t)&NRF_GPIOTE->TASKS_CLR[0]; " or "(uint32_t)&NRF_GPIOTE->TASKS_SET[0];" , the timing cost is almost zero!

-------------------------------------------------------------------------------

I have a new problem as below.

void TIMER2_config(void)
{
  NRF_TIMER2->TASKS_STOP = 1;	// Stop timer
  NRF_TIMER2->MODE = TIMER_MODE_MODE_Timer;  // taken from Nordic dev zone
  NRF_TIMER2->BITMODE = (TIMER_BITMODE_BITMODE_08Bit << TIMER_BITMODE_BITMODE_Pos);
  NRF_TIMER2->PRESCALER = 0;	// 1us resolution
  NRF_TIMER2->TASKS_CLEAR = 1; // Clear timer
  NRF_TIMER2->CC[0] = 1;					//*62.5ns
  NRF_TIMER2->CC[1] = 2;					//*62.5ns
NRF_TIMER2->CC[2] = 62;					//*62.5ns	
	
  NRF_TIMER2->INTENSET = (TIMER_INTENSET_COMPARE0_Enabled << TIMER_INTENSET_COMPARE0_Pos) |
													(TIMER_INTENSET_COMPARE1_Enabled << TIMER_INTENSET_COMPARE1_Pos) | 	
													(TIMER_INTENSET_COMPARE2_Enabled << TIMER_INTENSET_COMPARE2_Pos);  // taken from Nordic dev zone
  NRF_TIMER2->SHORTS = (TIMER_SHORTS_COMPARE0_CLEAR_Disabled << TIMER_SHORTS_COMPARE0_CLEAR_Pos)	|
											 (TIMER_SHORTS_COMPARE1_CLEAR_Disabled << TIMER_SHORTS_COMPARE1_CLEAR_Pos)	|
											 (TIMER_SHORTS_COMPARE2_CLEAR_Enabled << TIMER_SHORTS_COMPARE2_CLEAR_Pos);
}

void PPI_config(void)
{
		/*when TIMER2 CC0 = NUM , then pin =0*/
		NRF_PPI->CH[0].EEP  = (uint32_t)&NRF_TIMER2->EVENTS_COMPARE[0];     
//		NRF_PPI->CH[0].TEP  = (uint32_t)&NRF_GPIOTE->TASKS_OUT[0];    
			NRF_PPI->CH[0].TEP  = (uint32_t)&NRF_GPIOTE->TASKS_CLR[0];    
	
		/when TIMER2 CC1 = NUM , then pin = 1*/
		NRF_PPI->CH[1].EEP  = (uint32_t)&NRF_TIMER2->EVENTS_COMPARE[1];     
//		NRF_PPI->CH[1].TEP  = (uint32_t)&NRF_GPIOTE->TASKS_OUT[0];     		
			NRF_PPI->CH[1].TEP  = (uint32_t)&NRF_GPIOTE->TASKS_SET[0];     		
		/*when TIMER2 CC2 = NUM then TIMER2 stop*/
		NRF_PPI->CH[2].EEP  = (uint32_t)&NRF_TIMER2->EVENTS_COMPARE[2];     
		NRF_PPI->CH[2].TEP  = (uint32_t)&NRF_TIMER2->TASKS_STOP;				// Stop TIMER	
	
		NRF_PPI->CHEN       = (PPI_CHEN_CH0_Enabled << PPI_CHEN_CH0_Pos)	|
													(PPI_CHEN_CH1_Enabled << PPI_CHEN_CH1_Pos)	|
													(PPI_CHEN_CH2_Enabled << PPI_CHEN_CH2_Pos);
													
		NRF_GPIOTE->CONFIG[0] =((GPIOTE_CONFIG_MODE_Task << GPIOTE_CONFIG_MODE_Pos)
															|(CVSD_CTL  << GPIOTE_CONFIG_PSEL_Pos)
															|(GPIOTE_CONFIG_POLARITY_Toggle << GPIOTE_CONFIG_POLARITY_Pos)
															|(GPIOTE_CONFIG_OUTINIT_High     << GPIOTE_CONFIG_OUTINIT_Pos)); 
}

		int8_t bit_cnt;
		
		bit_cnt++;
		bit_cnt = bit_cnt & 0x01;
	
		bool	DIN_bit ;
		DIN_bit = bit_cnt;					    //for test

		NRF_TIMER2->CC[0] = 1;					
		NRF_TIMER2->CC[1] = 3;					
		NRF_TIMER2->CC[2] = 62;					

		nrf_gpio_pin_write (GPIO14, DIN_bit );	

		NRF_TIMER2->TASKS_START = 1;	// Start TIMER

GPIO14 is a sign, for check how log PPI CH0 works.

The question is ,

After "NRF_TIMER2->TASKS_START = 1;", the timing pass 400ns then PPI CH0 works.

How could it takes so much time?

In my imagine, PPI CH0 should response in 100ns , because CC[0]=1.

Austin

RE: How can I use 2 or more PPI channels to control 1GPIO?

Dmitry — Sun, 24 May 2020 14:09:43 GMT

For example, to make a low-polarity pulse:

		NRF_PPI->CH[0].EEP  = (uint32_t)&NRF_TIMER2->EVENTS_COMPARE[0];     
		NRF_PPI->CH[0].TEP  = (uint32_t)&NRF_GPIOTE->TASKS_CLR[0];    
	
		NRF_PPI->CH[1].EEP  = (uint32_t)&NRF_TIMER2->EVENTS_COMPARE[1];     
		NRF_PPI->CH[1].TEP  = (uint32_t)&NRF_GPIOTE->TASKS_SET[0];

RE: How can I use 2 or more PPI channels to control 1GPIO?

Austin (S.F.) — Sun, 24 May 2020 12:08:36 GMT

Hi Dmitry

How to setup ""a single GPIOTE channel (SET and CLR) from two different PPI channels"?

My code as below. Thanks a lot.

		
		NRF_PPI->CH[0].EEP  = (uint32_t)&NRF_TIMER2->EVENTS_COMPARE[0];     
		NRF_PPI->CH[0].TEP  = (uint32_t)&NRF_GPIOTE->TASKS_OUT[0];    
	
		NRF_PPI->CH[1].EEP  = (uint32_t)&NRF_TIMER2->EVENTS_COMPARE[1];     
		NRF_PPI->CH[1].TEP  = (uint32_t)&NRF_GPIOTE->TASKS_OUT[0];     		

		NRF_PPI->CH[2].EEP  = (uint32_t)&NRF_TIMER2->EVENTS_COMPARE[2];     
		NRF_PPI->CH[2].TEP  = (uint32_t)&NRF_TIMER2->TASKS_STOP;				// Stop TIMER	
	
		NRF_PPI->CHEN       = (PPI_CHEN_CH0_Enabled << PPI_CHEN_CH0_Pos)	|
													(PPI_CHEN_CH1_Enabled << PPI_CHEN_CH1_Pos)	|
													(PPI_CHEN_CH2_Enabled << PPI_CHEN_CH2_Pos);
													
		NRF_GPIOTE->CONFIG[0] =((GPIOTE_CONFIG_MODE_Task << GPIOTE_CONFIG_MODE_Pos)
															|(CVSD_CTL  << GPIOTE_CONFIG_PSEL_Pos)
															|(GPIOTE_CONFIG_POLARITY_Toggle << GPIOTE_CONFIG_POLARITY_Pos)
															|(GPIOTE_CONFIG_OUTINIT_High     << GPIOTE_CONFIG_OUTINIT_Pos));

Austin

RE: How can I use 2 or more PPI channels to control 1GPIO?

Dmitry — Sun, 24 May 2020 11:17:06 GMT

Hello,

you cannot assign two GPIOTE channels to the same pin, that won't work. But you can control different tasks of a single GPIOTE channel (SET and CLR) from two different PPI channels.