> Gesendet: Donnerstag, 11. Mai 2017 um 07:24 Uhr > Von: "Mike Looijmans" <mike.looijm...@topic.nl> > An: "Nathan Rossi" <nat...@nathanrossi.com>, "Arno Steffens" <s...@gmx.li> > Cc: meta-xilinx@yoctoproject.org > Betreff: Re: [meta-xilinx] SPI problem > > On 10-05-17 15:23, Nathan Rossi wrote: > > On 10 May 2017 at 17:18, Arno Steffens <s...@gmx.li> wrote: > >> Thanks Mike for the feedback. > >> It is an OnSemi Phyton camera chip. > >> Unfortunately FPGA is not suitable solution for me. The layout is already > >> fixed and I am not an FPGA expert. > >> Checking the SPI registers in Technical Manual: it seems that there is no > >> separate setting for CPOL/CPH for MOSI and MISO. > >> The only way I see is to send address, keep CS low, change SPI mode, read. > >> But there is another limitation. In struct spi_ioc_transfer there is a > >> setting: bits_per_word. I need 10 for doing that > >> as described for the first part (9 bit adress + 1 r/w bit). This returns > >> an error "could not transmit data". Any value expect 8 is returning an > >> error. > >> Is this a limitation by hardware or an issue in driver, which can be fixed? > > > > For the Zynq PS SPI controllers there is a hard limit to 8-bit words > > (kernel driver advertises this here: > > http://elixir.free-electrons.com/linux/latest/source/drivers/spi/spi-cadence.c#L565). > > > > If you need 10b words and you do not want to do it with an FPGA > > device, you can always use the kernels spi-bitbang module. But this is > > likely only good for low bandwidth control SPI, so if you are using > > SPI to pull image data from the camera this is probably not what you > > want. Also you could easily modify the spi-bitbang module to handle > > this CPOL inversion, such that it always samples MISO on the falling > > edge. > > Camera chips usually only use the SPI interface for configuration, so I'd go > with Nathan's suggestion and use Linux' bit-bang SPI controller for setting > camera parameters and such. Let the kernel pinmix the pins as GPIO and assign > them via devicetree to the bitbang controller. > > Kind regards, > > Mike Looijmans > System Expert
In fact it is just for configuration. Thanks, so it is clear that I can't hope to solve it without changing the bitstream (although remapping is not a big deal). Do you have an idea what frequency can be achieved by this driver? And I am a bit afraid of negative side-effect to more "realtime" related stuff on ARM. Kind regards Arno -- _______________________________________________ meta-xilinx mailing list meta-xilinx@yoctoproject.org https://lists.yoctoproject.org/listinfo/meta-xilinx
