The diagram of boot sequence

The premise of this sequence diagram is NuttX12.4.0, cxd56xx, non-SMP and Flat build.

The beginning of boot sequence is __start().

__start() will call nx_start(). nx_start() will initialize the kernel and call nsh_main(). nsh_main() will execute NuttShell(NSH). nx_start() is NuttX standard function, but the behavior depends on some kernel configurations. For example, the calling nsh_main() is also configurable. About related kernel configurations, see The list of related kernel configurations.

bootloader --> cxd56_start.c : Jump to __start by function call or de-assert the reset signal of CM4F note over cxd56_start.c : Initialize SP note over cxd56_start.c : Disable IRQ @processor level note over cxd56_start.c : Initialize .data/.bss note over cxd56_start.c : cxd56_board_initialize() as <arch>_board_initialize() cxd56_start.c --> nx_start.c : nx_start() note over nx_start.c : Initialize IDLE task TCB note over nx_start.c : nxsem_initialize() note over nx_start.c : Initialize HEAP note over nx_start.c : Create and initialize IDLE group instance note over nx_start.c : sched_lock() note over nx_start.c : fs_initialize() note over nx_start.c : irq_initialize() note over nx_start.c : clock_initialize() note over nx_start.c : timer_initialize() note over nx_start.c : nxsig_initialize() note over nx_start.c : nxmq_initialize() note over nx_start.c : net_initialize() note over nx_start.c : binfmt_initialize() note over nx_start.c : up_initialize() note over nx_start.c : drivers_initialize() note over nx_start.c : board_early_initialize() note over nx_start.c : Initialize SDIO for IDLE task nx_start.c --> nx_bringup.c : nx_bringup() note over nx_bringup.c : Initialize environment variables (PWD, PATH, LD_LIBRARY_PATH) note over nx_bringup.c : Start work queues nx_bringup.c --> nx_start_application : nx_start_task() note over nx_start_application : board_late_initialize() note over nx_start_application : coredump_initialize() note over nx_start_application : Start nsh_main() as the application initialization task note over nx_start.c : up_idle()