Jump to other application with SYS_INIT(PRE_KERNEL) is not working

[Ralf-Vention]

Hello community!

On my NRF I've got 2 applications on 2 locations in flash. Let's say I have application 1 on location 0x0 and application 2 on 0x32000. I always start first with application 1 and I check the state of a pin. If the pin is high, the nrf should jump to application 2.
This all works fine except for the fact that zephyr initializes a lot before the jump.

To avoid these initializations, I want to use SYS_INIT(early_function, EARLY, 0). But than the jump does not work. It does work when I use SYS_INIT(early_function, POST_KERNEL,0).

The code of early_function is shown below and is nothing special that cannot be done before the kernel is up and running if you ask me. Does anybody have any idea why I cannot execute the early_function PRE_KERNEL or even EARLY in sys_init?
Thank you in advance!

`
void early_function(void){

uint32_t vector_table = 0x32000;
uint32_t *app_code = (uint32_t *)vector_table;
uint32_t *app_sp = app_code[0];
uint32_t app_pc = app_code[1];
__set_MSP(app_sp);
void *start;
start = (void*)app_pc;
((void (*)(void))start)();

}
`

[ndrs-pst]

@Ralf-Vention, does this relate to the possibility that application might use some drivers before they are initialized, given that most drivers are initialized in PRE_KERNEL_1

[Ralf-Vention]

Hi @ndrs-pst,
Thank you for your reply!
That should not matter since application 2 should initialize everything itself because it's a standalone zephyr application (with an address offset)

[ndrs-pst]

@Ralf-Vention, based on your statement, "I always start first with application 1 and I check the state of a pin." it seems you are directly accessing the GPIO register without using a driver. Is that correct?

Alternatively, if that's not the case, you might consider adjusting the initialization sequence to isolate the issue.
The relevant section of the Zephyr Project documentation might provide some insights:

zephyr/include/zephyr/init.h

Lines 156 to 171 in 3fc5d97

	/**
	* @brief Obtain the ordinal for an init level.
	*
	* @param level Init level (EARLY, PRE_KERNEL_1, PRE_KERNEL_2, POST_KERNEL,
	* APPLICATION, SMP).
	*
	* @return Init level ordinal.
	*/
	#define INIT_LEVEL_ORD(level) \
	COND_CODE_1(Z_INIT_EARLY_##level, (Z_INIT_ORD_EARLY), \
	(COND_CODE_1(Z_INIT_PRE_KERNEL_1_##level, (Z_INIT_ORD_PRE_KERNEL_1), \
	(COND_CODE_1(Z_INIT_PRE_KERNEL_2_##level, (Z_INIT_ORD_PRE_KERNEL_2), \
	(COND_CODE_1(Z_INIT_POST_KERNEL_##level, (Z_INIT_ORD_POST_KERNEL), \
	(COND_CODE_1(Z_INIT_APPLICATION_##level, (Z_INIT_ORD_APPLICATION), \
	(COND_CODE_1(Z_INIT_SMP_##level, (Z_INIT_ORD_SMP), \
	(ZERO_OR_COMPILE_ERROR(0)))))))))))))

[Ralf-Vention]

I am not accessing the GPIO register directly but I deinitialize the driver before I jump to the other application. But that's not the issue. The issue is that application 1 initializes a lot at the startup of Zephyr and that once I jump to application 2 (bare metal) the zephyr initializations conflict with the application 2 initializations. I wanted to avoid this using SYS_INIT(EARLY){ jump to application 2 }. But for some reason that doesn't work

[ndrs-pst]

Since I don't know the details of application 1 and 2 so I would treat them as black boxes.

---

The following is the z_init section, which I captured from map files to provide insight into the initialization sequence.
Consequently, your early_function might not work if it is called before one of these steps in the sequence.

 *(SORT_BY_NAME(SORT_BY_ALIGNMENT(.z_init_EARLY?_*)))
 *(SORT_BY_NAME(SORT_BY_ALIGNMENT(.z_init_EARLY??_*)))
                0x0000000000025974                __init_PRE_KERNEL_1_start = .
 *(SORT_BY_NAME(SORT_BY_ALIGNMENT(.z_init_PRE_KERNEL_1?_*)))
 *(SORT_BY_NAME(SORT_BY_ALIGNMENT(.z_init_PRE_KERNEL_1??_*)))
 .z_init_PRE_KERNEL_130_0_
                0x0000000000025974        0x8 zephyr/kernel/libkernel.a(kheap.c.obj)
 .z_init_PRE_KERNEL_130_0_
                0x000000000002597c        0x8 zephyr/kernel/libkernel.a(mem_slab.c.obj)
 .z_init_PRE_KERNEL_140_00007_
                0x0000000000025984        0x8 zephyr/drivers/gpio/libdrivers__gpio.a(gpio_sam0.c.obj)
 .z_init_PRE_KERNEL_140_00008_
                0x000000000002598c        0x8 zephyr/drivers/gpio/libdrivers__gpio.a(gpio_sam0.c.obj)
 .z_init_PRE_KERNEL_140_00047_
                0x0000000000025994        0x8 zephyr/drivers/interrupt_controller/libdrivers__interrupt_controller.a(intc_sam0_eic.c.obj)
 .z_init_PRE_KERNEL_140_00052_
                0x000000000002599c        0x8 zephyr/drivers/dma/libdrivers__dma.a(dma_sam0.c.obj)
 .z_init_PRE_KERNEL_140_00075_
                0x00000000000259a4        0x8 zephyr/drivers/gpio/libdrivers__gpio.a(gpio_sam0.c.obj)
 .z_init_PRE_KERNEL_150_00066_
                0x00000000000259ac        0x8 zephyr/drivers/watchdog/libdrivers__watchdog.a(wdt_sam0.c.obj)
 .z_init_PRE_KERNEL_155_00054_
                0x00000000000259b4        0x8 zephyr/drivers/serial/libdrivers__serial.a(uart_sam0.c.obj)
 .z_init_PRE_KERNEL_155_00056_
                0x00000000000259bc        0x8 zephyr/drivers/serial/libdrivers__serial.a(uart_sam0.c.obj)
 .z_init_PRE_KERNEL_155_00058_
                0x00000000000259c4        0x8 zephyr/drivers/serial/libdrivers__serial.a(uart_sam0.c.obj)
 .z_init_PRE_KERNEL_160_00059_
                0x00000000000259cc        0x8 zephyr/drivers/counter/libdrivers__counter.a(counter_sam0_tc32.c.obj)
 .z_init_PRE_KERNEL_160_0_
                0x00000000000259d4        0x8 zephyr/drivers/console/libdrivers__console.a(uart_console.c.obj)
                0x00000000000259dc                __init_PRE_KERNEL_2_start = .
 *(SORT_BY_NAME(SORT_BY_ALIGNMENT(.z_init_PRE_KERNEL_2?_*)))
 .z_init_PRE_KERNEL_20_0_
                0x00000000000259dc        0x8 zephyr/drivers/timer/libdrivers__timer.a(cortex_m_systick.c.obj)
 *(SORT_BY_NAME(SORT_BY_ALIGNMENT(.z_init_PRE_KERNEL_2??_*)))
                0x00000000000259e4                __init_POST_KERNEL_start = .
 *(SORT_BY_NAME(SORT_BY_ALIGNMENT(.z_init_POST_KERNEL?_*)))
 .z_init_POST_KERNEL0_0_
                0x00000000000259e4        0x8 zephyr/libzephyr.a(shell_uart.c.obj)
 *(SORT_BY_NAME(SORT_BY_ALIGNMENT(.z_init_POST_KERNEL??_*)))
 .z_init_POST_KERNEL40_0_
                0x00000000000259ec        0x8 zephyr/lib/libc/newlib/liblib__libc__newlib.a(libc-hooks.c.obj)
 .z_init_POST_KERNEL40_0_
                0x00000000000259f4        0x8 zephyr/kernel/libkernel.a(system_work_q.c.obj)
 .z_init_POST_KERNEL50_00017_
                0x00000000000259fc        0x8 zephyr/drivers/pwm/libdrivers__pwm.a(pwm_sam0_tc.c.obj)
 .z_init_POST_KERNEL50_00051_
                0x0000000000025a04        0x8 zephyr/drivers/rtc/libdrivers__rtc.a(rtc_sam0.c.obj)
 .z_init_POST_KERNEL50_00062_
                0x0000000000025a0c        0x8 zephyr/drivers/pwm/libdrivers__pwm.a(pwm_sam0_tcc.c.obj)
 .z_init_POST_KERNEL50_00070_
                0x0000000000025a14        0x8 zephyr/drivers/flash/libdrivers__flash.a(flash_sam0.c.obj)
 .z_init_POST_KERNEL50_00104_
                0x0000000000025a1c        0x8 zephyr/drivers/i2c/libdrivers__i2c.a(i2c_sam0.c.obj)
 .z_init_POST_KERNEL70_00093_
                0x0000000000025a24        0x8 zephyr/drivers/spi/libdrivers__spi.a(spi_sam0.c.obj)
 .z_init_POST_KERNEL70_00102_
                0x0000000000025a2c        0x8 zephyr/drivers/spi/libdrivers__spi.a(spi_sam0.c.obj)
 .z_init_POST_KERNEL75_00096_
                0x0000000000025a34        0x8 zephyr/drivers/gpio/libdrivers__gpio.a(gpio_mcp23sxx.c.obj)
 .z_init_POST_KERNEL80_00068_
                0x0000000000025a3c        0x8 zephyr/drivers/can/libdrivers__can.a(can_sam0.c.obj)
 .z_init_POST_KERNEL80_00095_
                0x0000000000025a44        0x8 zephyr/drivers/fram/libdrivers__fram.a(fram_cy15x.c.obj)
 .z_init_POST_KERNEL80_00097_
                0x0000000000025a4c        0x8 zephyr/drivers/flash/libdrivers__flash.a(spi_nor.c.obj)
                0x0000000000025a54                __init_APPLICATION_start = .
 *(SORT_BY_NAME(SORT_BY_ALIGNMENT(.z_init_APPLICATION?_*)))
 *(SORT_BY_NAME(SORT_BY_ALIGNMENT(.z_init_APPLICATION??_*)))
 .z_init_APPLICATION90_0_
                0x0000000000025a54        0x8 zephyr/subsys/mgmt/mcumgr/mgmt/libsubsys__mgmt__mcumgr__mgmt.a(mgmt.c.obj)
 .z_init_APPLICATION90_0_
                0x0000000000025a5c        0x8 zephyr/subsys/mgmt/mcumgr/transport/libsubsys__mgmt__mcumgr__transport.a(smp.c.obj)
                0x0000000000025a64                __init_SMP_start = .
 *(SORT_BY_NAME(SORT_BY_ALIGNMENT(.z_init_SMP?_*)))
 *(SORT_BY_NAME(SORT_BY_ALIGNMENT(.z_init_SMP??_*)))
                0x0000000000025a64                __init_end = .