Early GPIO initialisation before main()

Question

Is there a way to initialise a GPIO earlier than in main() without modifying NCS/zephyr code? 
 We tried an PRE_KERNEL_1 init() function, but this is rather late still. 
 Might partially be due to CONFIG_ENTROPY_CC3XX=y ( https://devzone.nordicsemi.com/f/nordic-q-a/81498/nrf52840-startup-delay ). 
 Is there a way to get before CRYPTOCELL and RNG initialisation? 
 
 NCS2.0.2 
 nRF52840 
 matter

Sigurd · Accepted Answer

Hi, 
 It should be possible to get it lower than 400ms. Here is what I measure with the hello_world sample on nRF52840-DK: 
 
 Could be that you have some other things running before your application starts-up, e.g. MCUBoot 
 So you could try adding this early_init code to your board files. You can do it similar to how it's done here for adp5360_init.c, https://github.com/nrfconnect/sdk-nrf/blob/v2.1.0/boards/arm/thingy91_nrf9160/CMakeLists.txt#L7 
 but something like this instead: if(CONFIG_MCUBOOT)
	zephyr_library()
	zephyr_library_sources(your_early_init.c)
endif()

Sigurd · Answer

Hi, 
 We tried an PRE_KERNEL_1 init() function, but this is rather late still. 
 
 The initialization level is PRE_KERNEL_1 , but you can try to increase the initialization priority for the init funcion as well. E.g. 
 
 CONFIG_KERNEL_INIT_PRIORITY_DEVICE-10 (lower values indicate earlier initialization)

Early GPIO initialisation before main()

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