Cannot output high frequency signal via PWM

RE: Cannot output high frequency signal via PWM

hmolesworth — Fri, 10 Nov 2023 00:57:10 GMT

Ok, maybe also boost the pin strength:

Change
      NRF_GPIO_PIN_S0S1,
tp
      NRF_GPIO_PIN_H0H1,

Edit: Ok, why would I suggest this as if you are just driving the pin high or low with no clock then drive strength is pretty unimportant for a pin even with a large capacitor connected. The reason is earlier I think you suggested the pin driver (the internal FET) might have been damaged, which is quite possible. The internal FET driving the pin high or low with a modest RDSon resistance might have vaporised; magically it can be repaired (actually replaced) with a spare internal FET in parallel which happens to have a lower RDSon and hence stronger drive high or low.

RE: Cannot output high frequency signal via PWM

Drew — Thu, 09 Nov 2023 15:58:35 GMT

Hey hmolesworth,

At this point I am just attempting to get P0.18 to get set high, rather than worrying about the PWM signal, now that I have found the PWM code works when selecting another pin, so the capacitor should be ruled out as an issue. Relevant code snippets below:

#define FL_CLK_PIN NRF_GPIO_PIN_MAP(0,18)


    nrf_gpio_cfg	(
      FL_CLK_PIN,
      NRF_GPIO_PIN_DIR_OUTPUT,
      NRF_GPIO_PIN_INPUT_DISCONNECT,
      NRF_GPIO_PIN_NOPULL,
      NRF_GPIO_PIN_S0S1,
      NRF_GPIO_PIN_NOSENSE
    );
    
    
    nrf_gpio_pin_set(FL_CLK_PIN);

Also I have confirmed that the relevant memory locations in the UICR seem to have the correct values. Memory read outputs below:

C:\Program Files (x86)\Nordic Semiconductor\nrf-command-line-tools\bin>nrfjprog -f nrf52 --memrd 0x10001200
0x10001200: FFFFFFFF                              |....|

C:\Program Files (x86)\Nordic Semiconductor\nrf-command-line-tools\bin>nrfjprog -f nrf52 --memrd 0x10001204
0x10001204: FFFFFFFF                              |....|

RE: Cannot output high frequency signal via PWM

hmolesworth — Thu, 09 Nov 2023 01:15:50 GMT

Did you check for a capacitor fitted on that pin? If not it might be killing the signal ..

UICR is flash memory and flash memory bits can only be "programmed" low, not high; high requires a flash erase which means more than just one memory location. For this command to work would imply nrfjprog first reads the UICR, then erases it, then rewrites it with the original data save for that 1 location. Does nrfjprog actually do that?

nrfjprog -f nrf52 --memwr 0x10001200 --val 0xFFFFFFFF

More notes:

// User information configuration registers (UICR) are written in the same way as Flash. After UICR has been
// written, the new UICR configuration will only take effect after a reset.

// The Non-volatile memory controller (NVMC) is used for writing and erasing the internal Flash memory and
// the UICR.
// Before a write can be performed, the NVMC must be enabled for writing in CONFIG.WEN. Similarly, before
// an erase can be performed, the NVMC must be enabled for erasing in CONFIG.EEN. The user must make sure
// that writing and erasing are not enabled at the same time. Failing to do so may result in unpredictable behavior.
// Writing to Flash
// When writing is enabled, the Flash is written by writing a full 32-bit word to a word-aligned address in the
// Flash.
// The NVMC is only able to write '0' to bits in the Flash that are erased, that is, set to '1'. It cannot write back a
// bit to '1'.

RE: Cannot output high frequency signal via PWM

Drew — Wed, 08 Nov 2023 22:48:12 GMT

Hey Snoopy, way ahead of you. Been doing that for most of my testing for a while, and had no luck unfortunately. And thank you for all of your suggestions, they have been greatly appreciated.

RE: Cannot output high frequency signal via PWM

snoopy20 — Wed, 08 Nov 2023 22:42:33 GMT

Sorry must have typed at the same time and missed your reply. Can you set the pin high (disable pwm code) and see if there's a level high from it?

RE: Cannot output high frequency signal via PWM

Drew — Wed, 08 Nov 2023 22:31:08 GMT

As I said, I have read the output of the location after each of my changes, and confirmed that there was no change when its value was set to 0x00000000, or 0xFFFFFFFF

RE: Cannot output high frequency signal via PWM

snoopy20 — Wed, 08 Nov 2023 22:29:23 GMT

Read the memory location first...

RE: Cannot output high frequency signal via PWM

Drew — Wed, 08 Nov 2023 22:28:27 GMT

I am starting to worry perhaps I have a HW issue, perhaps something happened to burn out this one pin. I will get a second board set up to test on.

RE: Cannot output high frequency signal via PWM

Drew — Wed, 08 Nov 2023 22:27:26 GMT

After I ran your command the output was 0, no change to behavior. I also tried with 0x10001200 set to 0 as well. And with both set to all F's, none allowed the pin to function as GPIO.

RE: Cannot output high frequency signal via PWM

snoopy20 — Wed, 08 Nov 2023 22:25:24 GMT

Read the output of that memory location?

Sorry my value=0 was wrong, try nrfjprog -f nrf52 --memwr 0x10001200 --val 0xFFFFFFFF

RE: Cannot output high frequency signal via PWM

Drew — Wed, 08 Nov 2023 21:41:23 GMT

Hey Snoopy, gave this a try as well. There was no change.

RE: Cannot output high frequency signal via PWM

snoopy20 — Wed, 08 Nov 2023 18:35:28 GMT

Same thing then

infocenter.nordicsemi.com/index.jsp

nrfjprog -f nrf52 --memwr 0x10001200 --val 0

Edit:

That didn't copy/paste properly. The pin is disabled by default apparently but somehow you have the opposite.

PSELRESET[n] (n=0..1)

Address offset: 0x200 + (n × 0x4)

Mapping of the nRESET function (see POWER chapter for details)

All PSELRESET registers have to contain the same value for a pin mapping to be valid. If values are not the same, there will be no nRESET function exposed on a GPIO. As a result, the device will always start independently of the levels present on any of the GPIOs.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID				C																										B	A	A	A	A	A
Reset 0xFFFFFFFF				1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1
ID	Access	Field	Value ID	Value								Description
A	RW	PIN		18								GPIO pin number onto which nRESET is exposed
B	RW	PORT		0								Port number onto which nRESET is exposed
C	RW	CONNECT										Connection
			Disconnected	1								Disconnect
			Connected	0								Connect

RE: Cannot output high frequency signal via PWM

hmolesworth — Wed, 08 Nov 2023 18:32:43 GMT

Often there is a huge (exaggerating) capacitor to Gnd on the reset pin which can clobber a high frequency signal output; worth a check ..

RE: Cannot output high frequency signal via PWM

Drew — Wed, 08 Nov 2023 18:30:05 GMT

Hey there, yes I've given this a shot and still no luck unfortunately.

RE: Cannot output high frequency signal via PWM

Drew — Wed, 08 Nov 2023 18:28:49 GMT

Hey Snoopy, I appreciate the tip. I'm using an 833, and it seems the NFC pins are P0.09 and P0.10, so no luck there unfortunately.

RE: Cannot output high frequency signal via PWM

hmolesworth — Wed, 08 Nov 2023 18:25:40 GMT

Yes, CONFIG_GPIO_AS_PINRESET is used to set the pin as a reset input, but it cannot reset the pin to be a general output. To force the pin back to a general i/o pin do an Erase All, which erases UICR, and of course ensure CONFIG_GPIO_AS_PINRESET is not defined.

    /* Configure GPIO pads as pPin Reset pin if Pin Reset capabilities desired. If CONFIG_GPIO_AS_PINRESET is not
      defined, pin reset will not be available. One GPIO (see Product Specification to see which one) will then be
      reserved for PinReset and not available as normal GPIO. */
    #if defined (CONFIG_GPIO_AS_PINRESET)
        if (((NRF_UICR->PSELRESET[0] & UICR_PSELRESET_CONNECT_Msk) != (UICR_PSELRESET_CONNECT_Connected << UICR_PSELRESET_CONNECT_Pos)) ||
            ((NRF_UICR->PSELRESET[1] & UICR_PSELRESET_CONNECT_Msk) != (UICR_PSELRESET_CONNECT_Connected << UICR_PSELRESET_CONNECT_Pos))){
            NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Wen << NVMC_CONFIG_WEN_Pos;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NRF_UICR->PSELRESET[0] = 18;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NRF_UICR->PSELRESET[1] = 18;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Ren << NVMC_CONFIG_WEN_Pos;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NVIC_SystemReset();
        }
    #endif

RE: Cannot output high frequency signal via PWM

snoopy20 — Wed, 08 Nov 2023 18:24:05 GMT

Unsure of your chip but if it's a 832 or higher the NFC pins are enabled by default and iirc they are on 16 and 17, or 17 and 18, something like that.

See NFCPINS, and you can set it using nrfjprog.

infocenter.nordicsemi.com/index.jsp

RE: Cannot output high frequency signal via PWM

Drew — Wed, 08 Nov 2023 18:17:27 GMT

A little more information. Based off my research, I have removed CONFIG_GPIO_AS_PINRESET from my projects preprocessor macros. I have also run the following:

nrfjprog -e

Then built and downloaded my project onto my board, but I still could not output the PWM to P0.18, or even set the pin to high like a normal GPIO.

I also ran:

nrfjprog --readuicr uicr.hex

and have attached the resulting file below.

devzone.nordicsemi.com/.../8321.uicr.hex

RE: Cannot output high frequency signal via PWM

Drew — Wed, 08 Nov 2023 17:34:56 GMT

Hey there, after some experimentation, I found that the core issue with my code is the pin that I am using. NRF_GPIO_PIN_MAP(0,18), which also happens to be the MCU reset line. The same code generates the expected signal on NRF_GPIO_PIN_MAP(0,17). So it seems either that pin cannot output a PWM signal, or it requires some additional configuration.

Do you know if there is any configuration that I can do to get the signal to output from NRF_GPIO_PIN_MAP(0,18)?

Thanks,

Drew

RE: Cannot output high frequency signal via PWM

Einar Thorsrud — Mon, 06 Nov 2023 12:00:33 GMT

Hi,

What snoopy20 suggested could be a good solution. Another solution if you want a simple fixed duty-cycle PWM signal is to use TIMER and PPI, as is done by the PWM library.

That said, I think I see the issue in your code. You are providing the duty cycle in the format used for individual configs (nrf_pwm_values_individual_t), but used load mode common. When I test your code and set NRF_PWM_LOAD_INDIVIDUAL instead of NRF_PWM_LOAD_COMMON, I get the expected 50% duty cycle.

RE: Cannot output high frequency signal via PWM

snoopy20 — Fri, 03 Nov 2023 16:38:45 GMT

If you're happy to break out of the helper libraries here's some code that'll do it.

  #define CFG_PWM_INVERT (1 << 15)
  uint16_t nrf_pwm_duty[4] = {CFG_PWM_INVERT, CFG_PWM_INVERT, CFG_PWM_INVERT, CFG_PWM_INVERT};

  NRF_PWM0->COUNTERTOP = CFG_PWM_COUNT << PWM_COUNTERTOP_COUNTERTOP_Pos; // 100 = 16MHz/100 = 160KHz
  NRF_PWM0->DECODER = (PWM_DECODER_LOAD_Individual << PWM_DECODER_LOAD_Pos) | (PWM_DECODER_MODE_RefreshCount << PWM_DECODER_MODE_Pos);
  NRF_PWM0->SEQ[0].PTR = ((uint32_t) nrf_pwm_duty) << PWM_SEQ_PTR_PTR_Pos;
  NRF_PWM0->SEQ[0].CNT = (sizeof(nrf_pwm_duty) / sizeof(uint16_t)) << PWM_SEQ_CNT_CNT_Pos;
  NRF_PWM0->SEQ[1].PTR = ((uint32_t) nrf_pwm_duty) << PWM_SEQ_PTR_PTR_Pos;
  NRF_PWM0->SEQ[1].CNT = (sizeof(nrf_pwm_duty) / sizeof(uint16_t)) << PWM_SEQ_CNT_CNT_Pos;
  NRF_PWM0->SHORTS = PWM_SHORTS_LOOPSDONE_SEQSTART0_Enabled << PWM_SHORTS_LOOPSDONE_SEQSTART0_Pos;
  NRF_PWM0->PSEL.OUT[CFG_PWM_OUTPUT_USB_NUM] = (CFG_PIN_POWERMANAGER_USB_DAC << PWM_PSEL_OUT_PIN_Pos) | (PWM_PSEL_OUT_CONNECT_Connected << PWM_PSEL_OUT_CONNECT_Pos);
  NRF_PWM0->PSEL.OUT[CFG_PWM_OUTPUT_FRONT_NUM] = (CFG_PIN_POWERMANAGER_FRONT_DAC << PWM_PSEL_OUT_PIN_Pos) | (PWM_PSEL_OUT_CONNECT_Connected << PWM_PSEL_OUT_CONNECT_Pos);
  NRF_PWM0->PSEL.OUT[CFG_PWM_OUTPUT_REAR_NUM] = (CFG_PIN_POWERMANAGER_REAR_DAC << PWM_PSEL_OUT_PIN_Pos) | (PWM_PSEL_OUT_CONNECT_Connected << PWM_PSEL_OUT_CONNECT_Pos);
  NRF_PWM0->PSEL.OUT[CFG_PWM_MPPT_DAC_NUM] = (CFG_PIN_MPPT_DAC << PWM_PSEL_OUT_PIN_Pos) | (PWM_PSEL_OUT_CONNECT_Connected << PWM_PSEL_OUT_CONNECT_Pos);
  NRF_PWM0->LOOP = 1 << PWM_LOOP_CNT_Pos;
  NRF_PWM0->ENABLE = PWM_ENABLE_ENABLE_Enabled << PWM_ENABLE_ENABLE_Pos;
  NRF_PWM0->TASKS_SEQSTART[0] = PWM_TASKS_SEQSTART_TASKS_SEQSTART_Trigger << PWM_TASKS_SEQSTART_TASKS_SEQSTART_Pos;

Set CFG_PWM_COUNT to your period, 1/f

And then use

nrf_pwm_duty[CFG_PWM_MPPT_DAC_NUM] = CFG_PWM_INVERT | duty;

Where duty is 50% of your period.

For example 160KHz, use period = 100 and duty = 50.

Enjoy.

RE: Cannot output high frequency signal via PWM

Einar Thorsrud — Fri, 03 Nov 2023 14:06:39 GMT

Hi,

I did not immediately spot the issue so I need to test on my end on Monday. I will get back to you then.