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]

You should always configure the external crystal if you intend to use it. Some peripheral blocks/drivers will automatically configure it for you but many will run on the HF internal RC which would be a bad idea for pwm. According to the spec the timers run off the whatever the current HF CLK is.

With regard to your board, there will ALWAYS be an external 16MHz crystal. This is because it is required for bluetooth communications. However you still have to configure it otherwise the chip will default to 16MHz RC clk.

Your module has very few direct connections to gpio. In this manner it is COMPLETELY different from the DK. You need to specify which pins you are using since what I see in the schematic is some very aggressive filtering of the gpio output for things labeled "pwm" and the other stuff is designed as "open collector". "open collector" is a rather odd and very outdated choice since BJT's are pretty bad at switched signals when compared to fet's.