How to use PWM Sequence for complex LED control ( n times dimming and then stop )

[bluemountain]

Hi Nordic, 

I want to implement a LED blinking like below pseudo code. 
I'd like to use PWM sequence Timer x n , GPIOTE, PPI since it doesn't consume any CPU time. 

for (10 times) {
    for (100 times) }
        LED_ON  : 0.4ms
        LED_OFF : 0.6ms
    }
   LED_OFF : 200ms
}   

Is there any example for Timer, GPIOTE, and PPI coding ?

nRF52840DK board
nRF Connect SDK 3.0.1

Regards, 
Kenny

[Turbo J]

You could just use a PWM peripherial for this task. Should be simple.

If you used the RTC timer, you would achieve a lot less current consumtion in the off time - because the HF(int) oscillator can sleep. It can't when TIMER or PWM was active.

[bluemountain]

Hi Turbo, 


As your suggestion, I've tried to make the LED control with PWM. But, I couldn't make it. 
I had used PWM and sequence, but it just show about 1s ON without any blinking. 

Can you see the code below and what I got wrong ?


This is what I want to do

 * for ( n_blink  ) {                       // 'n_blink' for number of visual toggle

 *  for ( n_fast_blink ) {                  // 'fast' for LED bright control

 *    led on :    t_fast_on_us   us         //     t_fast_on_us + t_fast_off_us makes 't_on' since LED toggles very fast

 *    led off  :   t_fast_off_us   us

 *   }

 *    led off : t_off_us   us               // 't_off'

 * }

    led_blinkx2_conf(

        /* n_f_blinks  */ 10,           

        /* t_f_on_us   */ 100*1000,

        /* t_f_off_us  */ 100*1000, 

        /* n_blink     */ 5,            

        /* t_off_us    */ 200*1000 

    );

Settings

Read-back
NRF_PWM0->PSEL.OUT[0] = 0x0000000D 13
NRF_PWM0->PSEL.OUT[1] = 0xFFFFFFC0 -64
NRF_PWM0->PSEL.OUT[2] = 0xFFFFFFC0 -64
NRF_PWM0->PSEL.OUT[3] = 0xFFFFFFC0 -64
NRF_PWM0->MODE = 0x00000000 0
NRF_PWM0->PRESCALER = 0x00000007 7
NRF_PWM0->DECODER = 0x00000000 0

NRF_PWM0->COUNTERTOP = 0x000061A8 25000
NRF_PWM0->SEQ[0].PTR = 0x2000105A 536875098
NRF_PWM0->SEQ[0].CNT = 0x0000000A 10
NRF_PWM0->SEQ[0].REFRESH = 0x00000002 2
NRF_PWM0->SEQ[0].ENDDELAY = 0x000061A8 25000
NRF_PWM0->LOOP = 0x00000004 4
NRF_PWM0->ENABLE = 0x00000001 1
PWM_SEQ
PWM_SEQ [ 000 ] = 0x000030D4 12500
PWM_SEQ [ 001 ] = 0x000030D4 12500
PWM_SEQ [ 002 ] = 0x000030D4 12500
PWM_SEQ [ 003 ] = 0x000030D4 12500
PWM_SEQ [ 004 ] = 0x000030D4 12500
PWM_SEQ [ 005 ] = 0x000030D4 12500
PWM_SEQ [ 006 ] = 0x000030D4 12500
PWM_SEQ [ 007 ] = 0x000030D4 12500
PWM_SEQ [ 008 ] = 0x000030D4 12500
PWM_SEQ [ 009 ] = 0x000030D4 12500
PWM_SEQ [ 010 ] = 0x000030D4 12500
PWM_SEQ [ 011 ] = 0x000030D4 12500
PWM_SEQ [ 012 ] = 0x000030D4 12500
PWM_SEQ [ 013 ] = 0x000030D4 12500
PWM_SEQ [ 014 ] = 0x000030D4 12500
PWM_SEQ [ 015 ] = 0x000030D4 12500
PWM_SEQ [ 016 ] = 0x000030D4 12500
PWM_SEQ [ 017 ] = 0x000030D4 12500
PWM_SEQ [ 018 ] = 0x000030D4 12500
PWM_SEQ [ 019 ] = 0x000030D4 12500

What I got

LED keeps blinking about 5Hz. 

But it never stops. 

[Vidar Berg]

Please try with the sample posted here: RE: Softblink in NCS/Zephyr  

[bluemountain]

Thanks,. 

I replaced NRFX_PWM_PIN_NOT_USED  with   NRF_PWM_PIN_NOT_CONNECTED. to fix a compile error. After that, I compiled and flashed the code onto nRF52840. The LED dimming works great, but it keeps dimming continuously without stop. 

(void)nrfx_pwm_complex_playback(&pwm_instance, &led_on_seq, &led_off_seq, 1,
NRFX_PWM_FLAG_LOOP);
The fourth parameter '1' is the playback count, which should go into the LOOP register. 
From what I understand, this should control the number of dimming cycles. So, the LED should stop after one dimming cycle. 
And if I change the value to 3, the LED should dim three times and then stop. 

However, no matter what number I use, the LED never stops dimming. 

Could you please check the code and teach me how to correctly specify the number of dimming cycles?

--> 

After I change  NRFX_PWM_FLAG_LOOP  to  NRFX_PWM_FLAG_STOP, LED dimming stops. 
I'll study the code and check the register settings in detail. 

I'll open new ticket when I have another question. 
Please close this ticket. 

Note. 
The title of this ticket does not match with the contents. So, I changed it. 

Best Regards,