Is it possible to use P0.00 and P0.01 for I2C? I'm using RTC for LFCLK, so I thought these would be available as GPIO.

RE: Is it possible to use P0.00 and P0.01 for I2C? I'm using RTC for LFCLK, so I thought these would be available as GPIO.

James H — Thu, 03 Jan 2019 06:12:11 GMT

I'm using the Arduino core in PlatformIO, but following your suggestion I added this during configuration and it is now working. clockState and clockSource are temporary global variables I can watch in the debugger as I don't have UART connected. I can see the clock source change, although the clock never starts even though the start trigger shows up. I then can communicate with the I2C device.

if (clockState) {
      NRF_CLOCK->TASKS_LFCLKSTOP = 1;
      while(NRF_CLOCK->LFCLKSTAT);
    }
    clockState = NRF_CLOCK->LFCLKSTAT;
    clockSource = NRF_CLOCK->LFCLKSRCCOPY;
    NRF_CLOCK->LFCLKSRC = CLOCK_LFCLKSRC_SRC_RC;  
    NRF_CLOCK->TASKS_LFCLKSTART = 1;
    clockRun = NRF_CLOCK->LFCLKRUN;
    while(!NRF_CLOCK->LFCLKSTAT);
    clockState = NRF_CLOCK->LFCLKSTAT;
    clockSource = NRF_CLOCK->LFCLKSRCCOPY;
   }

RE: Is it possible to use P0.00 and P0.01 for I2C? I'm using RTC for LFCLK, so I thought these would be available as GPIO.

hmolesworth — Wed, 02 Jan 2019 22:26:27 GMT

RE: Is it possible to use P0.00 and P0.01 for I2C? I'm using RTC for LFCLK, so I thought these would be available as GPIO.

hmolesworth — Wed, 02 Jan 2019 21:55:00 GMT

Did you try the code I posted above? This is (typically) the default code, pins used for crystal not io; how are you setting LFCLK?

// <o> CLOCK_CONFIG_LF_SRC  - LF Clock Source

// <0=> RC
// <1=> XTAL
// <2=> Synth

#ifndef CLOCK_CONFIG_LF_SRC
#define CLOCK_CONFIG_LF_SRC 1
#endif

nrf_clock_lf_src_set((nrf_clock_lfclk_t)CLOCK_CONFIG_LF_SRC);

The board .h default (for PCA10040 for example):

// Low frequency clock source to be used by the SoftDevice
#define NRF_CLOCK_LFCLKSRC      {.source        = NRF_CLOCK_LF_SRC_XTAL,            \
                                 .rc_ctiv       = 0,                                \
                                 .rc_temp_ctiv  = 0,                                \
                                 .accuracy     = NRF_CLOCK_LF_ACCURACY_20_PPM}

RE: Is it possible to use P0.00 and P0.01 for I2C? I'm using RTC for LFCLK, so I thought these would be available as GPIO.

James H — Wed, 02 Jan 2019 21:14:16 GMT

I have set the LFCLK to use the internal oscillator, but that doesn't seem to be all that is needed.

RE: Is it possible to use P0.00 and P0.01 for I2C? I'm using RTC for LFCLK, so I thought these would be available as GPIO.

Nguyen Hoan Hoang — Wed, 02 Jan 2019 21:00:45 GMT

Those pins are for the 32KHz crystal of the RTC but default. If you want to use those pins as gpio, you need to remap them and use internal RC for your timer.

RE: Is it possible to use P0.00 and P0.01 for I2C? I'm using RTC for LFCLK, so I thought these would be available as GPIO.

hmolesworth — Wed, 02 Jan 2019 18:08:48 GMT

Worth checking the settings, have a look at this code:

    // 32kHz Osc pins can be used as GPIOs or 32kHz Oscillator, special case
    if ( (PinId == RCC_OSC_OUT_PIN) && (NRF_CLOCK->LFCLKSRC & 0x000001) ) return "RTC-OSC-OUT";
    if ( (PinId == RCC_OSC_IN_PIN)  && (NRF_CLOCK->LFCLKSRC & 0x000001) ) return "RTC-OSC-IN";

Typically the pins are set to RTC mode by functions invoked by this:

    // Configure RTC
    lfclk_config();

__STATIC_INLINE void nrf_clock_lf_src_set(nrf_clock_lfclk_t source)
{
    NRF_CLOCK->LFCLKSRC =
        (uint32_t)((source << CLOCK_LFCLKSRC_SRC_Pos) & CLOCK_LFCLKSRC_SRC_Msk);
}