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?

[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?.

[AmbystomaLabs]

Per my question above you should read over page 32 of the nrf51822 spec: 4.2 Timer/counters (TIMER) The timer/counter runs on the high-frequency clock source (HFCLK) and includes a 4 bit (1/2X) prescaler that can divide the HFCLK. The TIMER will start requesting the 1 MHz mode of the HFCLK for values of the prescaler that gives fTIMER less or equal to 1 MHz. If the timer module is the only one requesting the HFCLK, the system will automatically switch to using the 1 MHz mode resulting in a decrease in the current consumption. See the parameters I1v2XO16,1M, I1v2XO32,1M, I1v2RC16,1M in Table 32 on page 47 and ITIMER0/1/2,1M in Table 52 on page 61. The task/event and interrupt features make it possible to use the PPI system for timing and counting tasks between any system peripheral including any GPIO of the device. The PPI system also enables the TIMER task/event features to generate periodic output and PWM signals to any GPIO. The number of input/outputs used at the same time is limited by the number of GPIOTE channels.