Early GPIO initialisation before main()

[mabe]

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]

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)

[mabe]

Using a priority of 41 does not help with the timing.
Using a priority of 40 creates a kernel panic:

00> [00:00:00.408,111] <err> os: r0/a1:  0x00000004  r1/a2:  0x000002d4  r2/a3:  0x2002ec18
00> [00:00:00.408,111] <err> os: r3/a4:  0x00000000 r12/ip:  0x00000000 r14/lr:  0x00020ba5
00> [00:00:00.408,111] <err> os:  xpsr:  0x61000000
00> [00:00:00.408,111] <err> os: s[ 0]:  0x00000000  s[ 1]:  0x00000000  s[ 2]:  0x00000000  s[ 3]:  0x00000000
00> [00:00:00.408,111] <err> os: s[ 4]:  0x00000000  s[ 5]:  0x00000000  s[ 6]:  0x00000000  s[ 7]:  0x00000000
00> [00:00:00.408,111] <err> os: s[ 8]:  0x00000000  s[ 9]:  0x00000000  s[10]:  0x00000000  s[11]:  0x00000000
00> [00:00:00.408,111] <err> os: s[12]:  0x00000000  s[13]:  0x00000000  s[14]:  0x00000000  s[15]:  0x00000000
00> [00:00:00.408,111] <err> os: fpscr:  0x00000000
00> [00:00:00.408,111] <err> os: Faulting instruction address (r15/pc): 0x000a70f4
00> [00:00:00.408,111] <err> os: >>> ZEPHYR FATAL ERROR 4: Kernel panic on CPU 0
00> [00:00:00.408,111] <err> Àì )

[Sigurd]

mabe said:

Using a priority of 41 does not help with the timing.

Could you explain this some more? How early do you need it ?Why is it not early enough now?

mabe said:

Using a priority of 40 creates a kernel panic:

That makes sense, since the GPIO driver is initialized at that priority (CONFIG_KERNEL_INIT_PRIORITY_DEFAULT)

[Ioannis.Pallis]

We need to initialize and set a Gpio to high in the first 300ms or earlier. Using priority 41, we achieve 900ms. We know that the clock and crypto initialization takes time. Is there any way to start prior to them?  

[Sigurd]

Hi,

In that case, I would skip using the Zephyr GPIO API, and use the nrf_gpio_ HAL API directly.

You can see how we have done it in e.g. this file: https://github.com/nrfconnect/sdk-zephyr/blob/main/boards/arm/nrf9160dk_nrf52840/board.c#L217

If you don't have a device-tree node for your gpio, a simplified function could look something like this:

#include <hal/nrf_gpio.h>

#define MY_PIN 3

static int early_init(const struct device *dev)
{
	nrf_gpio_cfg_output(MY_PIN);
	nrf_gpio_pin_set(MY_PIN);
	return 0;
}

SYS_INIT(early_init, PRE_KERNEL_1, 0);

[Ioannis.Pallis]

thanks for your reply. I tried it and the pin is set to high after 400ms now. 

[Sigurd]

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()