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Re: [Paparazzi-devel] Suggestions

From: Ben Laurie
Subject: Re: [Paparazzi-devel] Suggestions
Date: Fri, 13 Dec 2013 20:54:29 +0000

On 13 December 2013 13:40, Alexandre Bustico
<address@hidden> wrote:
> Le 13/12/2013 14:28, Ben Laurie a écrit :
>> This is because the cost of context switches in RT
>> OSes is very high compared to the cost of function calls and
>> occasional timer checks...
> With chibios on stm32f4, context switching @ 1khz in the worst case : using
> hardware float unit (so that float registers have to be saved),
> have a cost of 0.1%, so 99.9% for your tasks, 0,1% for the system, when you
> are in position where you miss theses 0.1%, you're in big trouble :-)

Process switching is not the only context switching, of course -
interrupts also cause context switches (and we used to avoid those,
too). But, to be fair, Paparazzi on Linux still uses h/w interrupts...

> "big" mcu, are designed for rtos, there is dedicated timer for the systick,
> and dedicated hardware for making context switch easy and fast.
> --
> Alexandre
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