51822 PWM unstable

[Blue]

Hi guys，

I use the 51822's PWM recently, PWM is made by GPIOTE+PPI+TIMER, and the PWM source code as below(I use TIMER1, GPIOTE[0], PPI_CH[0], PPI_CH[1]， period and duty means ticks with 16MHz):

void startPwm1(uint16_t period, uint16_t duty)
{
	NRF_TIMER1->INTENCLR = TIMER_INTENSET_COMPARE0_Enabled << TIMER_INTENSET_COMPARE0_Pos; 
	NVIC_DisableIRQ(TIMER1_IRQn);
	
	NRF_GPIOTE->CONFIG[0] = GPIOTE_CONFIG_MODE_Task << GPIOTE_CONFIG_MODE_Pos |
							GPIOTE_CONFIG_POLARITY_Toggle << GPIOTE_CONFIG_POLARITY_Pos |
							WAVE_PWM << GPIOTE_CONFIG_PSEL_Pos | 
							GPIOTE_CONFIG_OUTINIT_Low << GPIOTE_CONFIG_OUTINIT_Pos;
	
	NRF_PPI->CH[0].EEP = (uint32_t) &NRF_TIMER1->EVENTS_COMPARE[0];
	NRF_PPI->CH[0].TEP = (uint32_t) &NRF_GPIOTE->TASKS_OUT[0];
	
	NRF_PPI->CH[1].EEP = (uint32_t) &NRF_TIMER1->EVENTS_COMPARE[1];
	NRF_PPI->CH[1].TEP = (uint32_t) &NRF_GPIOTE->TASKS_OUT[0];
	NRF_PPI->CHENSET = (PPI_CHENSET_CH0_Enabled << PPI_CHENSET_CH0_Pos) | (PPI_CHEN_CH1_Enabled<< PPI_CHEN_CH1_Pos);
	
	NRF_TIMER1->TASKS_STOP = 1;
	NRF_TIMER1->TASKS_CLEAR = 1;
	
//	NRF_TIMER1->PRESCALER = 0;
	NRF_TIMER1->CC[0] = period;  	
	NRF_TIMER1->CC[1] = period - duty;	
	NRF_TIMER1->SHORTS = TIMER_SHORTS_COMPARE0_CLEAR_Enabled << TIMER_SHORTS_COMPARE0_CLEAR_Pos;
	NRF_TIMER1->INTENCLR = TIMER_INTENSET_COMPARE0_Enabled << TIMER_INTENSET_COMPARE0_Pos; 
	NRF_TIMER1->TASKS_START = 1;
}

When I download the program to the development board, PWM works well(period is 842 ticks, duty is 20 ticks), As shown below：

Then power off the development board， and connected other 3.3V power supply to any 51822's GPIO port, then disconnected, power the development board, Now the PWM does not work well, as show below:

1 pwm works well, 3 looks like Inverted. It seems like GPIOTE's response is not in time.

So have you encountered this situation?

[AmbystomaLabs]

It's not clear from your code if you are requesting (ie, starting HFCLK_EXT). The nRF will always run from internal HFCLK which is not accurate, you have to request HFCLK EXT.

If you are using an SD then you request it through an API command, otherwise you can just set up the clock registers and pclk source.

Also, I assume your comment about powering through gpio port was just a typo, right? You meant just applying vdd from external source.

[Blue]

1, My board does not have an external crystal, I use the internal crystal.

static void ble_stack_init(void) { uint32_t err_code;

nrf_clock_lf_cfg_t clock_lf_cfg = **NRF_CLOCK_LFCLKSRC**;

    // Initialize SoftDevice.
    SOFTDEVICE_HANDLER_INIT(&clock_lf_cfg, NULL);
    ......

}

#define NRF_CLOCK_LFCLKSRC      {.source        = NRF_CLOCK_LF_SRC_RC,            \
                                 .rc_ctiv       = 16,                                \
                                 .rc_temp_ctiv  = 2,                                \
                                 .xtal_accuracy = NRF_CLOCK_LF_XTAL_ACCURACY_20_PPM}

[Blue]

2, I am using sdk 12.3/examples/ble_peripheral/ble_app_uart and using an SD, and my application is not set on clock registers, The application starts, I configure the timer1 like this：

  NRF_TIMER1->PRESCALER = 0;
NRF_TIMER1->MODE = TIMER_MODE_MODE_Timer;
NRF_TIMER1->BITMODE = TIMER_BITMODE_BITMODE_16Bit<<TIMER_BITMODE_BITMODE_Pos;

[Blue]

3, The process is like this：

power the board , download the program, PWM work properly now.

power off the board, use another 3.3V power supply touch any GPIO pin , and then disconnect.

power the board , this time, PWM work is not normal.

It seems that PWM is very sensitive to electrical interference.

[Blue]

Hi, AmbystomaLabs ,

The reason is power_manager () function in while(1), When pwm is working, I need to disable power_manager () function, then pwm works well.

Now the pwm works well on nrf51 DK board, and the time control is very accurate, such as I set the PWM period to 800 ticks(800/16M = 50us)，and set the PWM duty to 20 ticks(20 /16M = 1.25us), I find the PWM works well through the logic analyzer.

But I encountered a new problem on our own board, the PWM duty can not be controlled, it is smaller than the value I set, and the smaller value will be some changes, such as :
I set the PWM duty to 20 ticks(1.25us), In fact, there is no PWM output;
I set the PWM duty to 60 ticks(3.75us), In fact, I find the PWM duty is perhaps 1.5us or greater than 1.5us or less than 1.5us;

Can you help me, What information do I need to provide? Such as PCB?.