__pinned_bss in assete tracker_v2

[mexco]

I testing asset_tracker_v2. I observed that during debug, the execution enters the init.c file. As well __pinned_bss, __boot_func etc are used in this file.

1. What is purpose of __pinned_bss ?

2. Where the entery point has been declared / confugured for init.c. 

3. In the switch_to _main_thread()... function, prepare_multithreading has been passed as an argument. How the thread created and handled in Zephyr ?

4. What is __weak Main   ?

5. what is sys_rand_fallback ?

6. Various functions are defined in init.c , what is sequence of these functions when used at boot time ?

[Håkon Alseth]

Hi,

 

1. What is purpose of __pinned_bss ?

This is an architect specific feature, which we do not use:

https://docs.zephyrproject.org/3.0.0/reference/kconfig/CONFIG_LINKER_USE_PINNED_SECTION.html

 

BSS is the zero-initialized RAM section: https://en.wikipedia.org/wiki/Data_segment

2. Where the entery point has been declared / confugured for init.c. 

3. In the switch_to _main_thread()... function, prepare_multithreading has been passed as an argument. How the thread created and handled in Zephyr ?

You can read more about the os and its scheduling here:

https://docs.zephyrproject.org/latest/reference/kernel/scheduling/index.html

And threads here:

https://docs.zephyrproject.org/latest/reference/kernel/threads/index.html

 

4. What is __weak Main   ?

A weak symbol is a default handler that can be overridden:

https://en.wikipedia.org/wiki/Weak_symbol

 

5. what is sys_rand_fallback ?

Please see the comment in the specific section: https://github.com/nrfconnect/sdk-zephyr/blob/v2.7.99-ncs1/kernel/init.c#L360-L364

Note that zephyr is a project that supports many architectures and devices, so not all is relevant for nRF devices.

6. Various functions are defined in init.c , what is sequence of these functions when used at boot time ?

I would recommend that you enter debug mode and step through the sequence if you are interested in this.

 

Kind regards,

Håkon