Dear Dmitry,

In message CAHs5x+N5O2zuO9C+12w2Ci7LF6r7Zupop2Sq+Cy9PDR5o=CwLA@mail.gmail.com you wrote:

I'm looking at u-boot source code, and see a huge amount of hardware drivers, used only for the loader. On the other side, modern Linux kernels eat a more than half of RAM on cheap embedded modules like HLK-R04.

Is it suitable to morph u-boot into tiny embedded microkernel OS adding multitasking scheduler or share its drivers for i/o with some other tiny RTOS?

No, it is not.

I recommend reading the U-Boot Design Principles [1]; many of these focus on being easy to port to new hardware and/or bring up new hardware, and to favour simple code over complex functionality.

From the beginning, a strictly single-threaded design has been

assumed. By adding multi-task support you would have to introduce locking conecpts and - even more difficult - to review the whole code base. Also, the implementation frequently assumes it's single-tasking - for example, a large number of device drivers use simple polling techniques which are OK for single-task systems, but which would hurt like hell if you hade several parallel tasks.

The situation is simple: If youneed an OS, then boot one. If only minimal OS functionality is needed, then boot a simple OS.

[1] http://www.denx.de/wiki/U-Boot/DesignPrinciples

Best regards,

Wolfgang Denk