I will use an ARM processor from Atmel, do not yet know the exact model, but I know for a fact that the SPI controller included in their ARM processor supports slave mode. When I have more details on the hardware used will not forget to update the forum.
Thanks & Regards Carlo Bastelli ----- Original Message ----- From: "Marek Vasut" <marek.va...@gmail.com> To: "Bastelli Carlo" <carlo_baste...@yahoo.it> Cc: "Ned Forrester" <nforres...@whoi.edu>; "Fabio Estevam" <feste...@gmail.com>; <spi-devel-gene...@lists.sourceforge.net>; <linux-kernel@vger.kernel.org>; <linux-arm-ker...@lists.infradead.org> Sent: Saturday, August 25, 2012 1:44 PM Subject: Re: SLAVE Side SPI kernel driver development Dear Bastelli Carlo, > In my application in fact the slave is connected to the master without > other devices on the bus, a simple point to point, and receives a frame of > known dimensions. What hardware do you use? What CPU is it? > I think I will be very busy to read post in the coming days :) Good luck with that. > Thanks to all of you who provided suggestions. > Carlo Bastelli > > ----- Original Message ----- > From: "Ned Forrester" <nforres...@whoi.edu> > To: "Marek Vasut" <ma...@denx.de> > Cc: "Fabio Estevam" <feste...@gmail.com>; > <spi-devel-gene...@lists.sourceforge.net>; "Bastelli Carlo (yahoo)" > <carlo_baste...@yahoo.it>; <linux-kernel@vger.kernel.org>; > <linux-arm-ker...@lists.infradead.org> > Sent: Friday, August 24, 2012 6:54 PM > Subject: Re: SLAVE Side SPI kernel driver development > > On 08/24/2012 11:38 AM, Marek Vasut wrote: > > Dear Fabio Estevam, > > > >> On Fri, Aug 24, 2012 at 11:57 AM, Bastelli Carlo (yahoo) > > > > CCing SPI list > > > >> <carlo_baste...@yahoo.it> wrote: > >>> Hello, I'm Carlo, I have a difficult task at work, my boss asked me to > >>> develop > >>> > >>> a driver SPI slave side on embedded ARM processor running Linux. > >>> > >>> Precisely linux occur on the SPI bus as a slave, not master as > >>> required > >>> by the hierarchical structure of the current kernel. The new driver > >>> will > >>> > >>> receive via interrupt and respond when selected by its chip select. > > > > So a soft-spi ? It's gonna be slow as hell and unstable too. > > > >>> Can > >>> anyone suggest the best way to develop this driver? > > > > Get a CPU which has SPI-slave capable IP, start from there. If you were > > to implement soft-spi this way, you'd have to use FIQ on ARM, to be able > > to handle > > stuff with reasonable latency ... check how the ps/2-gpio driver is done > > in > > Linux ... I tried it, it barely worked, you don't want to go down that > > road. > > > >>> Personally, I > >>> > >>> have identified two main roads, the first if possible to exploit the > >>> structure SPI master driver > > > > Not happening. You'd have to split the parts from the struct spi_master > > into > > common and master-only parts. That's for starters. > > > >>> with a few tricks that now I can not > >>> define. The second most radical, write a driver for a UART like, but > >>> managing the SPI device. > >>> Thank you for any suggestions or examples. > > > > First of all, the SPI slave mode is COMPLETELY different from the master > > mode. > > You need to react on incoming CS-low ASAP, which might turn out to be a > > problem > > on it's own. Then, even if you do, you do not know how long the transfer > > is > > going to be, so you need to allocate enough buffers as the transfer > > progresses > > onwards. > > > > In case of your soft-spi, how do you plan to sample the CLK line to sync > > clock? > > > >> Marek got spi slave running on a mx28. See his patch: > >> http://www.spinics.net/lists/arm-kernel/msg190860.html > > > > This was tested (and developed) on this board: > > http://www.denx-cs.de/?q=M28 > > > > The userland code is really easy too, simply pump it into spidev or read > > from > > it. But all that is only possible because of the SPI IP in the mx28 is > > nice. > > > >> Regards, > >> > >> Fabio Estevam > > > > Best regards, > > Marek Vasut > > I generally agree with the above comments. A generalized SPI slave must > be able to respond instantly, often within one clock cycle. This can > only work in hardware, or in an OS like Linux when the activity on the > bus is completely predictable by the Linux slave. The only cases I know > of are streaming of data in a predictable way between a single master > and single slave (no other devices on the bus). > > This topic comes up periodically, but I don't think there has been any > change in the situation for all the time I've followed the discussion. > I recommend that you read the archives of this mailing list to > understand the limitations of a potential slave mode. The archives can > be found at: > > http://sourceforge.net/mailarchive/forum.php?forum_name=spi-devel-general > > then look for threads with "slave" in the subject in the following > months (I'd give thread start dates, but parts of the threads are > disconnected in the archives, and this is the easiest way to see all the > parts, day ranges are in parentheses): > > 2007/04 (13-18) > 2007/09/27 and 2007/10 (13-17) > 2009/03 (2-3) > 2009/12/18 and 2010/1/19 and 2010/02 (14-16) > 2010/07 (26) and 2010/08 (13) > 2011/01 (28-31) and 2011/02 (1-10) > 2011/10 (18) > 2012/06 (29-30 and 2012/07 (1-17) Best regards, Marek Vasut -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
