[Xenomai] a question:deadline for the real devices

[Xenomai] a question:deadline for the real devices

[ali hagigat]

When we talk about Xenomai and a hard real time system, every thing
seems OK regarding to tasks and the CPU code, what about the
functionality of I/O devices?

Like there is no guarantee for writing a sector on a hard disk below a
specified time. Or reading/writing a USB device.

I mean doing a real input/output action seems not to have a specific
deadline. While sometimes it seems we need to have it.

Any comment and direction will be appreciated much.

Re: [Xenomai] a question:deadline for the real devices

[Uwe Fechner]

 Hi,

for realtime I/O you need drivers that support Xenomai. They are available for serial I/O,
CAN bus, Ethercat and probably more.

Avoid USB (not as realiable as needed for industrial applications).

With respect to disc I/O: First of all use an SSD harddisc that has a RAM input cache.

Than you could also create a thread that receives data via a realtime queue and
writes it with a lower priority the hard disc. I am not sure if this is always
needed.

Best regards:

Uwe Fechner

On 24.06.2012 12:59, ali hagigat wrote:
> When we talk about Xenomai and a hard real time system, every thing
> seems OK regarding to tasks and the CPU code, what about the
> functionality of I/O devices?
>
> Like there is no guarantee for writing a sector on a hard disk below a
> specified time. Or reading/writing a USB device.
>
> I mean doing a real input/output action seems not to have a specific
> deadline. While sometimes it seems we need to have it.
>
> Any comment and direction will be appreciated much.
>
> _______________________________________________
> Xenomai mailing list
> Xenomai@xenomai.org
> http://www.xenomai.org/mailman/listinfo/xenomai


-- 
----------------------------------------
Uwe Fechner, M.Sc.
Delft University of Technology
Faculty of Aerospace Engineering/ASSET
Kluyverweg 1,
2629 HS Delft, The Netherlands
Phone: +31-15-27-88902

Re: [Xenomai] a question:deadline for the real devices

[Anders Blomdell]

On 06/24/2012 01:19 PM, Uwe Fechner wrote:
>   Hi,
>
> for realtime I/O you need drivers that support Xenomai. They are available for serial I/O,
> CAN bus, Ethercat and probably more.
Ethercat is most probaly not there since its licensing is incompatible 
with GPL (and most other open source licenses AFAICT).

/Anders