Sample project to demonstrate kernel space and user space

[Ubaid_M]

Hi,

I am using a nrf528409dk for my application development using nCS.
I have various features from which I need to understand how to add some high priority features into kernel space and some low priority features into user space.

Kindly share with me if any test or sample project demonstrating the above for me to work with.

Thanks,

Ubaid

[Simon]

As mentioned in the zephyr thread documentation, threads run in supervisor mode by default

In order to drop a thread down to user mode, set CONFIG_USERSPACE=y in the prj.conf file and crete the thread like done in the  hello_world_user sample

You need to use the K_USER option when creating the thread

Best regards,

Simon

[Ubaid_M]

Hi,

Can you point me towards thread creation in kernel space similarly.
I want to have both kernel space and user space threads in my app.

Simon said:

In order to drop a thread down to user mode

Thanks,

[Simon]

Just omit the K_USER option when creating the thread. See the following sample:

user_supervisor_mode_test.zip

It should give the following output:

*** Booting Zephyr OS build v3.1.99-ncs1  ***
user_function: UserSpace! (nrf52840dk_nrf52840)
supervisor_function: privileged mode. (nrf52840dk_nrf52840)

Best regards,

Simon

[Ubaid_M]

Thank you Simon,

1. What would be the ideal way to communicate between kernel threads and user threads..? Is it message queues..?

2. Does it make sense if I treat all peripheral (SPI, I2C, UART etc,.) handlers as individual kernel space threads and all application algorithms that consume the peripheral data as user space threads..?

Thanks,
Ubaid

[Simon]

Ubaid_M said:

1. What would be the ideal way to communicate between kernel threads and user threads..? Is it message queues..?

Yes, that could work. See  RE: Recommended best practice for a multithreaded sensor for other ways of thread communication.

Ubaid_M said:

2. Does it make sense if I treat all peripheral (SPI, I2C, UART etc,.) handlers as individual kernel space threads and all application algorithms that consume the peripheral data as user space threads..?

That could work. Here are some example use cases of Zephyr' user mode feature:

• The kernel can protect against many unintentional programming errors which could otherwise silently or spectacularly corrupt the system.

• The kernel can sandbox complex data parsers such as interpreters, network protocols, and filesystems such that malicious third-party code or data cannot compromise the kernel or other threads.

• The kernel can support the notion of multiple logical “applications”, each with their own group of threads and private data structures, which are isolated from each other if one crashes or is otherwise compromised.

Read more in https://developer.nordicsemi.com/nRF_Connect_SDK/doc/2.1.0/zephyr/kernel/usermode/overview.html#overview 

Best regards,

Simon

[Ubaid_M]

Thanks Simon, That was largely helpful.

As a last query of mine, if we take an example of nrf52840dk, which has onboard QSPI external flash.

Can I treat the internal flash here in, to work on kernel space only, while having the QSPI external flash to work on user space..?

If possible, has such a thing been done..?
Please help me with any sample project available for the same.

Thanks,

[Simon]

I'm not sure about this question. I will be gone now for a long time, so would you be able to open a new DevZone ticket about this?

Best regards,

Simon

[Ubaid_M]

Sure,Thanks