nRF52832 LFCLK external signal and soft device

Question

Hello, 
 I try to set up an external signal for the LFCLK on a nrf52832. From this question : 
 
 I know the nrf52832 can do this (signal on XL1 pin, XL2 grounded). 
 I know I must set the bits "bypass" and "external clock" in LFCLKSRC register. 
 
 But I don't know how to set these bits through the SDK functions, with a running soft device. 
 
 Defines like CLOCK_LFCLKSRC_BYPASS_xxx and CLOCK_LFCLKSRC_EXTERNAL_xxx dont exist in the SDK 11.0.0. 
 The function softdevice_handler_init() (through SOFTDEVICE_HANDLER_APPSH_INIT()) hasn't the required parameter in the nrf_clock_lf_cfg_t structure. 
 The function softdevice_handler_init() forces LFCLK configuration and the LFCLKSRC register can't be set after the soft device initialization. 
 
 Can someone give me a valid code example? 
 Thanks !

apuret · Accepted Answer

With other answers and some studying, I have found the solution: external clock signal must be connected to XL1 pin, XL2 pin may be left floating or be grounded (if the signal voltage isn't rail-to-rail), LFCLK MUST be configured for external clock signal and started BEFORE enabling the softdevice, the softdevice may now be initialized with NRF_CLOCK_LF_SRC_XTAL for the LFCLK. Here is a code example (for the nRF52832) : /* Defines not available in the SDK 11.0.0 */ /* Register: CLOCK_LFCLKSRC */ /* Description: Clock source for the LFCLK */ /* Bits 16 : Enable or disable bypass of LFCLK crystal oscillator with external clock source */ #define CLOCK_LFCLKSRC_BYPASS_Pos (16UL) /*!< Position of BYPASS field. */ #define CLOCK_LFCLKSRC_BYPASS_Msk (0x1UL << CLOCK_LFCLKSRC_SRC_Pos) /*!< Bit mask of BYPASS field. */ #define CLOCK_LFCLKSRC_BYPASS_Disabled (0UL) /*!< Disabled bypass */ #define CLOCK_LFCLKSRC_BYPASS_Enabled (1UL) /*!< Enable bypass */ /* Bits 17 : Enable or disable external source for LFCLK */ #define CLOCK_LFCLKSRC_EXTERNAL_Pos (17UL) /*!< Position of EXTERNAL field. */ #define CLOCK_LFCLKSRC_EXTERNAL_Msk (0x1UL << CLOCK_LFCLKSRC_SRC_Pos) /*!< Bit mask of EXTERNAL field. */ #define CLOCK_LFCLKSRC_EXTERNAL_Disabled (0UL) /*!< Disabled external source */ #define CLOCK_LFCLKSRC_EXTERNAL_Enabled (1UL) /*!< Enable external source */ /* Configuring LFCLK to use an external signal */ NRF_CLOCK->LFCLKSRC = (CLOCK_LFCLKSRC_SRC_Xtal << CLOCK_LFCLKSRC_SRC_Pos) | (CLOCK_LFCLKSRC_BYPASS_Enabled << CLOCK_LFCLKSRC_BYPASS_Pos ) | (CLOCK_LFCLKSRC_EXTERNAL_Enabled << CLOCK_LFCLKSRC_EXTERNAL_Pos); /* Starting LFCLK */ NRF_CLOCK->EVENTS_LFCLKSTARTED = 0; NRF_CLOCK->TASKS_LFCLKSTART = 1; while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0) { /* Nothing to do */ } /* Initialising softdevice with a 'crystal' for LFCLK source (and no scheduler) */ nrf_clock_lf_cfg_t clockLfCfg = { .source = NRF_CLOCK_LF_SRC_XTAL, .rc_ctiv = 0, .rc_temp_ctiv = 0, .xtal_accuracy = NRF_CLOCK_LF_XTAL_ACCURACY_20_PPM }; SOFTDEVICE_HANDLER_INIT(&clockLfCfg, NULL);