On Sun, 17 Jan 2016, Karlsson & Wang wrote:
> Date: Sun, 17 Jan 2016 16:37:21 +0100
> From: Karlsson & Wang <nicklas.karls...@karlssonwang.se>
> Reply-To: EMC developers <emc-developers@lists.sourceforge.net>
> To: Alec Ari <neotheu...@ymail.com>
> Cc: emc-developers@lists.sourceforge.net
> Subject: Re: [Emc-developers] RTAI ethernet
>
>> I believe the hostmot2 ethernet drivers only work (or at least have only
>> been tested) with PREEMPT_RT.
>>
>> Alec Ari
>
> PREEMPT_RT work but it is not possible to put the limit then it come to
> period of how often real time tasks could be executed. Without proper
> handling of interrupt every now and then there will be a delay by the time
> it take to execute the interrupt. I also expect sometimes several will
> happen at once and even though it is rare with a machine running several
> hours a day it happens sometimes.
Not true at all
On Preempt-RT, most hard interrupts are converted to preemptable kernel
threads with assignable priorities. On the average, Preempt-RT latency is not
quite as good as RTAI but specific versions of Preempt-RT are better than RTAI
and Preempt-RT is getting better all the time.
I have more than 2 machine years of hm2_eth uptime running under
Preempt-RT (with > 1 machine year running at 4 KHz) and have not had
any latency issues ( Peak round trip network jitter on the 4 KHz machine
is in the 30 usec region over a year of operation and running compiles,
youtube videos etc )
>
> I run software on microcontrollers with the Cortex-* CPU and sometimes use
> the nested interrupt controller as hardware scheduler and get in all essense
> perfect real time scheduling.
>
> Without proper handling of priorities for interrupts it is only possible to
> use a rather small percentage of available clock cycles for real time tasks
> since delay caused by interrupts must be added to real time tasks execution
> time.
>
>
> Nicklas Karlsson
>
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