[En-Nut-Discussion] Nut/OS Initialization

[Harald Kipp]

I'm opening this new topic to share my view about Nut/OS initialization, 
which is related to the latest discussion about NutRegisterDevice used 
on Ethernet devices.

Most operating systems handle device driver initialization different 
from Nut/OS. Most OSes include all required drivers, either directly 
linked to the kernel or dynamically loaded from external storage.

Nut/OS runs without external storage, dynamic loading/unloading is no 
option. In order to avoid rebuilding the kernel each time a new device 
is used, Nut/OS uses the linker to include just the device drivers used 
by the application. The link reference is provided by NutRegisterDevice().

Many tiny OSes use a similar approach. The other side of the coin is, 
that a number of initialization calls are needed at the beginning of 
main(). My initial intention had been to allow

int main(void)
{
   printf("Hello world!");
}

In fact, the Nut/OS version looks less beautiful:
http://www.ethernut.de/nutwiki/Hello_World!

As more complex devices are added, the main() routine becomes 
contaminated with system specific code.

One suggested solution would be to implement a callback function like 
HardwareInit(), which has to be included into the application 
"somewhere". IMHO, this is not more elegant than simply calling 
HardwareInit() at the beginning of main.

Another solution may be to find a compromise between both worlds. The 
Configurator may allow to preregister some initializations, like it is 
doing now with heap memory. So the user may select to use UART0 for 
stdin/stdout, the SMSC driver for Ethernet etc. Of course, changing 
devices requires a rebuild then. But in addition the application is 
still free to add more devices in the old way, without rebuilding the 
kernel.

On some hardware, stdio will always go to the first UART at 115200 Baud 
and, if the Ethernet driver is included in the CPU, exactly that 
Ethernet driver will be used, typically with DHCP. Why not pre-register 
these devices and services via the Configurator's .conf files (or 
hardware specific header files when building in the source tree without 
using the Configurator)?

Harald