Setting XL1 & XL2 as GPIO does not work.

Question

Hi there, We are not using external Crystal for this design and thinking of reusing XL1 & XL2 (Pin 0 and Pin 1) for SPI (MISO & MOSI). But I found that I can't set properly set these pins as GPIO output. Something as simple as: 
 nrf_gpio_cfg_output(0); nrf_gpio_pin_set(0); will not bring the line up (I checked with a scope). Are there additional steps needed to make these pins GPIO? Or, it's not possible to use them as regular GPIO? Thanks, Cecylia

Stian Røed Hafskjold · Accepted Answer

Hi, yes you have to make sure that LFCLKSRC is set to 0. If you haven't set this register in your project it defaults to 0 already. 
 Are you using custom HW or the PCA10056 DK? If you are using the DK pin 0 and 1 are routed to the crystal and you need to cut SB1/2 and solder SB3/4 in order to route the pins out to the GPIO header. Please check out the schematics or this list .

Cecylia · Answer

I'm using custom HW. I did not explicitly set the source ---or so I thought--- but the sdk_config.h that I copied over apparently set it to XTAL. So when I called 'nrf_drv_clock_init()' then it sets it to XTAL instead of RC. When I change this CLOCK_CONFIG_LF_SRC to 0 then I can use XL0 and XL1. Yay! Thanks! // 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

robert · Answer

The principle of nRF52 GPIO shared pin is: when a pin is enabled for certain function, the GPIO function is automatically disabled. So, when LFCLK is using external crystal, pin-0 and pin-1 GPIO function will be disabled automatically. That means you have to prevent LFCLK from using external crystal.

hmolesworth · Answer

I can give you a clue: 
 // 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";
 
 Search for this (NRF_CLOCK->LFCLKSRC) and you can see how to enable the pins for port io

Setting XL1 & XL2 as GPIO does not work.

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