From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 19 Jul 2007 08:33:08 +0000 (GMT) From: Mathieu JOINIE-MAURIN MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-1265041004-1184833988=:95898" Message-ID: <269393.95898.qm@domain.hid> Subject: [Xenomai-help] Re : Problem with rt_pipe and user space communication List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: xenomai@xenomai.org --0-1265041004-1184833988=:95898 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Hi,=0A=0ASo i tried again this morning by sending an array of 3 doubles on = my real time side (with rt_pipe_stream). On user space, I get as expected 2= 4 bytes which matches the size of 3 doubles. But I cannot get more datas an= d I still do not understand why. My real time function runs periodically ev= ery 1 ms and my userspace function runs in background or periodically (arou= nd 500ms). What do I do wrong so that when I use the read(2) function it on= ly reads datas by group (as if there was message boundary).=0A=0AThanks in = advance,=0A=0AMathieu=0A=0A----- Message d'origine ----=0ADe : Philippe Ger= um =0A=C0 : Mathieu JOINIE-MAURIN =0ACc= : xenomai@xenomai.org le : Mercredi, 18 Juillet 2007, 19h48mn = 37s=0AObjet : Re: [Xenomai-help] Problem with rt_pipe and user space commun= ication=0A=0AOn Wed, 2007-07-18 at 14:43 +0000, Mathieu JOINIE-MAURIN wrote= :=0A> Hi everybody,=0A> =0A> I try to learn Xenomai. I have a problem that = I do not understand. I=0A> want that my real time task to communicate with = my user space task=0A> through a pipe (FIFO) in order to save sample datas = in a file. My=0A> problem is the following. I create a pipe with:=0A=0A=0A> =0A> I get a value of 8 for nb_read which corresponds to sizeof(doub= le).=0A> But i am expecting more. I do not know why the system function rea= d(2)=0A> works like this.=0A> =0AThe user-space side seems to read double v= alues as soon as they are=0Awritten to the pipe (i.e. try sending two doubl= es in a row at each=0Akernel-side write op), so this behaviour would be the= expected one.=0A=0ASidenote: rt_pipe_stream will not keep message boundari= es (e.g. writing=0A8 + 4 + 4 may cause the read side to get 12 + 4); rt_pip= e_send/write=0Awill keep the boundaries intact.=0A=0A> Thank you in advance= for your help,=0A> =0A> Mathieu=0A> =0A> =0A> =0A> _______________________= _______________________________________________=0A> Ne gardez plus qu'une s= eule adresse mail ! Copiez vos mails vers=0A> Yahoo! Mail =0A> ____________= ___________________________________=0A> Xenomai-help mailing list=0A> Xenom= ai-help@domain.hid> https://mail.gna.org/listinfo/xenomai-help=0A-- =0APhil= ippe.=0A=0A=0A=0A=0A=0A=0A=0A=0A=0A __________________________________= ___________________________________________ =0ANe gardez plus qu'une seule = adresse mail ! Copiez vos mails vers Yahoo! Mail --0-1265041004-1184833988=:95898 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable

Hi,

So i tried again this morning by sending an= array of 3 doubles on my real time side (with rt_pipe_stream). On user spa= ce, I get as expected 24 bytes which matches the size of 3 doubles. But I c= annot get more datas and I still do not understand why. My real time functi= on runs periodically every 1 ms and my userspace function runs in backgroun= d or periodically (around 500ms). What do I do wrong so that when I use the= read(2) function it only reads datas by group (as if there was message bou= ndary).

Thanks in advance,

Mathieu

----- Messa= ge d'origine ----
De : Philippe Gerum <rpm@xenomai.org>
=C0 : M= athieu JOINIE-MAURIN <mjoiniem@domain.hid>
Cc : xenomai@xenomai.org
Envoy=E9 le : Me= rcredi, 18 Juillet 2007, 19h48mn 37s
Objet : Re: [Xenomai-help] Pro= blem with rt_pipe and user space communication

On Wed, 2007-07-= 18 at 14:43 +0000, Mathieu JOINIE-MAURIN wrote:
> Hi everybody,
&g= t;
> I try to learn Xenomai. I have a problem that I do not understa= nd. I
> want that my real time task to communicate with my user space= task
> through a pipe (FIFO) in order to save sample datas in a file= . My
> problem is the following. I create a pipe with:

<sni= p>
>
> I get a value of 8 for nb_read which corresponds to = sizeof(double).
> But i am expecting more. I do not know why the syst= em function read(2)
> works like this.
>
The user-space sid= e seems to read double values as soon as they are
written to the pipe (i= .e. try sending two doubles in a row at each
kernel-side write op), so t= his behaviour would be the expected one.

Sidenote: rt_pipe_stream will not keep m= essage boundaries (e.g. writing
8 + 4 + 4 may cause the read side to get= 12 + 4); rt_pipe_send/write
will keep the boundaries intact.

>= ; Thank you in advance for your help,
>
> Mathieu
>
= >
>
> ____________________________________________________= __________________
> Ne gardez plus qu'une seule adresse mail ! Copie= z vos mails vers
> Yahoo! Mail
> _____________________________= __________________
> Xenomai-help mailing list
> Xenomai-help@domain.hid= na.org
> https://mail.gna.org/listinfo/xenomai-help
--
Phili= ppe.

=0A=0A=0A=0A

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