[En-Nut-Discussion] improving the energy efficiency of ethernut.. :)

[Matthias Ringwald]

hi

I've attended a talk with the title "Improving the Energy Efficiency  
of the MANTIS Kernel"
by Cormac Duffy at the EWSN 07 conference. They figured out, that if  
a simple app runs
on the Mantis OS (a pre-emptive posix-like minimal OS, not such much  
different from nut/os)
and there is nothing to do, there is a thread switch to the IDLE thread
which in turns puts the CPU to sleep. Later, when something (e.g.  
IRQ) happens, the IDLE
thread continues but will immediately yield as there is another  
thread ready, yet
performing a second thread switch. In total, there are 2 thread- 
switches but none
are required. Even if there would be a switch to a different thread,  
only one
switch is required. After that, he explained that they removed the  
IDLE thread
and put its logic (which is almost non-existant in the nut/os idel  
thread) into
the scheduler/task switch logic... Et voila, energy is saved.

could not find the paper online, but you might as the author
http://www.comp.lancs.ac.uk/computing/users/roedig/pages/publications/ 
b2hd-ewsn07duffy.html

or read their techreport:
http://www.cs.ucc.ie/~cd5/publications/ 
Technical_report_cs-2006-27-11.pdf

besides energy, as it saves context-switches it could also make some  
apps faster.

comments ? :)

cheers,
matthias