RFC: RTOS for Calypso

[l--putt]

Hi!

Is AreasOfWork in the wiki still up to date? I intend to work on the UI 
(Sorry Dieter, GSM testset too expensive at the moment :( ) and want to 
choose a RTOS. A small collection that I came across:

FreeRTOS
     What is the problem?

TNKernel
http://www.tnkernel.com/tn_description.html
     Scheduler, Mutexes, Queues, etc. available
     strange (at least unfamiliar) API for memory

eCos
http://ecos.sourceware.org/about.html
     many target MCUs but are their any other than ARM in BB chipsets?
     powerful but complex (at least at first glance)

NUT/OS
http://www.ethernut.de/en/
     minimalistic RTOS, easy to port
     seems to have sound community
     familiar APIs: malloc, fopen's devices, ...
     cooperative multithreading: Is that OK? We still have IRQs for 
realtime...

Since we seem to barely need an OS, a full-blown OS like eCos seems 
excessive. For compatibility with MT6235 user space, malloc and fopen is 
the right direction. Hence, my favourite is NUT/OS. In fact, I tried 
porting it to calypso just for fun. With some wrappers, Osmocom's 
platform files can be used. Only turns on the backlight and occasionally 
outputs some bytes on the UART at the moment. However, I still call this 
success. It took me just a day from knowing nothing about NUT/OS and 
very little about calypso and ARM to do this. Seems promising in terms 
of portability and documentation to me.

Open question: How much overhead can we afford, i.e., how much spare 
time is there on the CPU? Does "Disable RTC interrupt as it causes lost 
TDMA frames" (layer1/init.c) indicate issues? (Yes, sorry, haven't read 
GSM specs yet...) If yes, is it reasonable to independently handle GSM 
stuff with FIQ and only give IRQ to whatever OS we choose?


Regards,
Stefan