User Mode and Supervisor mode

[orkunsengur]

The documentation says that: "By default, threads run in supervisor mode and allow access to privileged CPU instructions, the entire memory address space, and peripherals. User mode threads have a reduced set of privileges."

Also, these two modes are related to macros K_KERNEL_STACK and K_THREAD_STACK. In my CoAP(with Open-Thread) example that is provided from NRf-SDK, K_THREAD_STACK_SIZEOF is used. I think, this example choose user-mode threads. 

What is the reason? Can I choose supervisior mode? Documentation says that it is more efficient with using memory and has privileged access to memory space.    

[Didrik Rokhaug]

Hi,

What sample are you looking at, and what version of NCS are you using?

User mode is only enabled if CONFIG_USERSPACE is defined.

In the coap_client sample, CONFIG_USERSPACE is not defined (you can check this for yourself by searching for CONFIG_USERSPACE in <your build folder>/zephyr/.config).

 

In my CoAP(with Open-Thread) example that is provided from NRf-SDK, K_THREAD_STACK_SIZEOF is used.

 I could not find K_THREAD_STACK_SIZEOF being used in any of the Thread samples in NCS v1.5.0. Where did you find it?

Anyway, I expect it was used because it works for both kernel and user threads.

Best regards,

Didrik

[orkunsengur]

k_thread_create(&receive_thread_data, receive_stack_area,
K_THREAD_STACK_SIZEOF(receive_stack_area),
(k_thread_entry_t)coap_receive, NULL, NULL, NULL,
/* Lowest priority cooperative thread */
K_PRIO_COOP(CONFIG_NUM_COOP_PRIORITIES - 1), 0,
K_NO_WAIT);

It is written in this function. This function is called in coap_init function which is located in coap_utils.c

[Didrik Rokhaug]

As they are not using the K_USER flag, this is not a userspace thread.

Also, when CONFIG_USERSPACE is not enabled, the K_THREAD_STACK_* macros have the same effect as the K_KERNEL_STACK_* macros.