Use RESET pin as GPIO - nRF52840

[Candela]

Hi all,

I am developing an application for a custom board using the nRF52840. I need to use the reset pin (P0.18) as a regular GPIO, configured as an input with an associated interrupt. However, I am unable to set this pin as a GPIO. The steps I have followed are based on this thread.

My setup:

- First, I try to run the application on nRF52840dk

- I am using the Visual Studio nRF Connect extension, with version v2.3.0 for both toolchain and SDK to build the application.

- I flash the board using the following commands on a powershell terminal

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nrfjprog -e

west flash --softreset

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nrfjprog -e
west flash --softreset

Code configuration:

- I added CONFIG_GPIO_AS_PINRESET=n on prj.conf file

- Then, I added the following code before configuring the pin to turn on the disconnect flag on the PSELRESET registers

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#ifdef CONFIG_GPIO_AS_PINRESET

if (((NRF_UICR->PSELRESET[0] & UICR_PSELRESET_CONNECT_Msk) != (UICR_PSELRESET_CONNECT_Disconnected << UICR_PSELRESET_CONNECT_Pos)) ||

((NRF_UICR->PSELRESET[1] & UICR_PSELRESET_CONNECT_Msk) != (UICR_PSELRESET_CONNECT_Disconnected << 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 | (1 << 31);

while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}

NRF_UICR->PSELRESET[1] = 18 | (1 << 31);

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){}

// UICR changes require a reset to be effective

NVIC_SystemReset();

}

#endif

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#ifdef CONFIG_GPIO_AS_PINRESET
    if (((NRF_UICR->PSELRESET[0] & UICR_PSELRESET_CONNECT_Msk) != (UICR_PSELRESET_CONNECT_Disconnected << UICR_PSELRESET_CONNECT_Pos)) || 
          ((NRF_UICR->PSELRESET[1] & UICR_PSELRESET_CONNECT_Msk) != (UICR_PSELRESET_CONNECT_Disconnected << 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 | (1 << 31);
      while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
      NRF_UICR->PSELRESET[1] = 18 | (1 << 31);
      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){}
      // UICR changes require a reset to be effective
      NVIC_SystemReset();  
    }
#endif

Results:

After setting these configurations, I get CONFIG_GPIO_AS_PINRESET is not set after building the application, and I get a HARD FAULT debug event when the pin configuration is set.

How can I solve this problem?

Candela