Zephyr RTOS: How to create threads

The Zephyr RTOS has basically two methods to create a thread.

1. Using the kernel API

Just like the other RTOS such as FreeRTOS, we can use the kernel API to create a thread.

__syscall k_tid_t 
k_thread_create(struct k_thread  *new_thread,
                k_thread_stack_t *stack,
                size_t            stack_size,
                k_thread_entry_t  entry,
                void             *p1, 
                void             *p2, 
                void             *p3,
                int               prio, 
                uint32_t          options, 
                k_timeout_t       delay);

Detailed documentation of this API can be found here: https://docs.zephyrproject.org/latest/reference/kernel/threads/index.html#c.k_thread_create

The most interesting parameter to me is the delay option. The new thread can be scheduled immediately or for a delayed start.

• delay — Scheduling delay, or K_NO_WAIT (for no delay).

When tasks are created from the application task (e.g.init_task), it is common to assign the init task with a higher priority than the other tasks to be created in the init task to avoid preemption during initialization.

2. Using K_THREAD_DEFINE macro

K_THREAD_DEFINE(thread_id, STACKSIZE, thread_entry_point, NULL, NULL, NULL, PRIORITY, 0, 0);

This might look unfamiliar but others like uItron or OSEK have a similar concept of static creation of Task at compile time.