OS overhead

Angelo Fraietta angelo_f at bigpond.com
Mon Nov 25 21:12:21 UTC 2002

I have done some minor testing as I am using RTEMS as the OS for a 
musical instrument.
My system has two boards - a PIC microcontroller for I/O and a 40MHz 
386sx running RTEMS at 1000 ticks per microsecond.

I tested the amount of time an input went from the input of the I/O 
board, through the RTEMs system through an ISR which woke up a task, and 
back up through the I/O (I used a simple feedback mechanism). I measured 
a 3 to 4 millisecond propagation total. (the value flickered between 3 
and 4 on the oscilloscope).

I have previously measured the propagation from the I/O card to the ISR 
and measured 250us (this value therefore must be multiplied by three due 
to my inter-board communication), which means a minimum of 750us for 
inter board comms. The scanning of inputs takes approximately 2ms. The 
RTEMS overhead would effectively be > 3ms - (750us + 2ms) < 4ms - (750us 
+ 2ms).

I have not done exhaustive tests yet, but I hope that this is of some 
help to you.

azzedine wrote:

>Hi all,
>Has anybody got documentations about  overhead measurements with RTEMS OS
>(N tasks with HPF scheduling)?
>I looking for implementations examples of real time systems with temporal
>analysis (tasks time execution + OS time overhead), is there anybody who can
>provide me such cases studies ?
>Azzedine Abdenour
>PH.D student
>LESTER/Universite de Bretagne Sud
>Lorient, France

Angelo Fraietta

PO Box 859
Hamilton NSW 2303

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