Setting XL1 & XL2 as GPIO does not work.

RE: Setting XL1 & XL2 as GPIO does not work.

martijnthe — Fri, 21 Dec 2018 20:21:44 GMT

When using the current SDK (15.2) and the SoftDevice, you probably also need to set the `NRF_SDH_CLOCK_LF_SRC` to 0, as well as configure the related `NRF_SDH_CLOCK_LF_...` configuration options.

RE: Setting XL1 & XL2 as GPIO does not work.

Cecylia — Wed, 13 Jun 2018 00:55:35 GMT

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!

// <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

RE: Setting XL1 & XL2 as GPIO does not work.

Cecylia — Wed, 13 Jun 2018 00:53:20 GMT

Thanks for clarifying!

RE: Setting XL1 & XL2 as GPIO does not work.

Stian Røed Hafskjold — Tue, 12 Jun 2018 12:26:29 GMT

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.

RE: Setting XL1 & XL2 as GPIO does not work.

robert — Tue, 12 Jun 2018 07:41:25 GMT

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.

RE: Setting XL1 & XL2 as GPIO does not work.

Cecylia — Tue, 12 Jun 2018 04:49:37 GMT

Hi @hmolesworth, thanks for the answer. I don't have any "(NRF_CLOCK->LFCLKSRC)" anywhere in my project. Do you have specific example project in mind for me to search those?
Specifically the comments "// 32kHz Osc pins can be used as GPIOs or 32kHz Oscillator, special case" that might give me clearer clues.

From what you wrote, though, does it mean that if I set LFCLKSRC to 0 then the pins are free for GPIO?

RE: Setting XL1 & XL2 as GPIO does not work.

hmolesworth — Fri, 08 Jun 2018 02:21:48 GMT

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