From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <5114E175.4080908@siemens.com> Date: Fri, 08 Feb 2013 12:28:53 +0100 From: Jan Kiszka MIME-Version: 1.0 References: <5113BFD0.7050501@hilscher.com> <5113D225.8030900@xenomai.org> <5114C05B.7040507@hilscher.com> <5114C302.5020209@xenomai.org> In-Reply-To: <5114C302.5020209@xenomai.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Xenomai] Hilscher driver for cifX boards List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix , =?UTF-8?B?U3TDqXBoYW5lIExPUw==?= Cc: xenomai@xenomai.org On 2013-02-08 10:18, Gilles Chanteperdrix wrote: > On 02/08/2013 10:07 AM, St=C3=A9phane LOS wrote: >=20 >> Le 07/02/2013 17:11, Gilles Chanteperdrix a =C3=A9crit : >>> On 02/07/2013 03:53 PM, St=C3=A9phane LOS wrote: >>> >>>> Hello Sirs, >>>> >>>> Hilscher is offering a Linux driver based on UIO for cifX boards. >>>> >>>> In my understanding, down to 1ms cycle time, a PREEMPT RT solution >>>> should be enough. >>>> >>>> The cifX boards can manage with bus cycle times down to 250=C2=B5s l= ike with >>>> EtherCAT or Sercos III firmwares. >>>> >>>> So it seems in that cases that using Xenomai would be the way to go. >>>> I suppose that it would be needed to modify or change the existing >>>> driver but I can't figure out how things (Xenomai / RTDM / UIO) fit >>>> together. >>>> >>>> UIO is the kernel module that allows the mapping of the board memory= to >>>> user space. >>>> >>>> The cifX driver uses the libpciaccess to pick up the board and retri= eve >>>> some board information from UIO before the mapping. >>>> Then it uses pthread and rt functions when accessing the board. >>>> >>>> Since UIO and libpciaccess are only used during the initialization, = is >>>> it a problem for a Xenomai application ? >>>> >>>> We have setup a Xenomai system and tried to compile the user land >>>> library with Xenomai options and flags and it seems we have been suc= cessful. >>>> The driver should be using the POSIX skin of Xenomai if we have been= lucky. >>>> >>>> I can't see why we would need RTDM. Any hint please ? >>>> >>>> I am an absolute beginner in the Xenomai arena, don't throw me to th= e >>>> lions... >>>> >>> >>> If UIO is used to register an interrupt handler for instance, the >>> interrupt handler will not be called in real-time context when used w= ith >>> Xenomai, so, you would have to use the (deprecated) native or posix s= kin >>> services to register a user-space interrupt handler, or more likely >>> write an RTDM driver. On the other hand, if what you need is simply >>> accessing the board registers through MMIO, then you do not need RTDM. >>> >>> While accessing registers from user-space may be tempting, there is a >>> risk of ending up with an application where the driver code is not >>> clearly separated. Writing a driver separated from the application is >>> preferable, as it provides a sane isolation between the two. If you >>> change the hardware, you just have to rewrite a driver which follows = the >>> same profile, if you want to write another application using the same >>> driver, you can keep the driver. >>> >> >> Thank you for your kind support Gilles. >> >> The cifX Device Driver is Hilscher's library to deal with cifX boards=20 >> and is available for the major OSes. >> Additionally it is available to anybody as source code, the cifX Drive= r=20 >> Toolkit when one has to create a driver for his own OS. >> >> This driver library accesses the board interface which is a Dual Port=20 >> Memory. >> >> So the user application shall use this layer and gets independence fro= m=20 >> the target OS. >> >> I understand that we should create an RTDM driver instead of a UIO=20 >> driver and adapt the user library so that it uses the RTDM driver. >=20 >> >> Am I right ? >=20 >=20 > I tried to explain why it may be better to create an RTDM driver, but i= n > this case this may not be the best option. The answer to your question > depends on what you have to do to implement the driver. As I said, if > you simply have to access MMIO registers, user-space may be fine, if yo= u > have to handle interrupts kernel-space (so, RTDM) is preferable. Are we talking about linux/drivers/uio/uio_cif.c here? That one obviously has interrupt support. If your customers may want to use Xenomai 3 with I-pipe instead of Preempt-RT underneath (both options will exist), RTDM will still be required for interrupt handling. If you like to, you could propose such a driver for Xenomai integration. That would ensure it will come with future releases. I also wonder if it didn't make sense for us to provide an UIO-like infrastructure for such use cases (single-user device drivers with IRQ event channel needs). Jan --=20 Siemens AG, Corporate Technology, CT RTC ITP SDP-DE Corporate Competence Center Embedded Linux