Date: Thu, 21 Feb 2013 17:30:03 +0100 From: Bernd Walter <ticso@cicely7.cicely.de> To: Patrick Kelsey <kelsey@ieee.org> Cc: Aleksandr Rybalko <ray@freebsd.org>, Bernd Walter <ticso@cicely7.cicely.de>, freebsd-arm@freebsd.org, freebsd-mips@freebsd.org, ticso@cicely.de Subject: Re: SPI, _sz fields in struct spi_command Message-ID: <20130221163003.GC12189@cicely7.cicely.de> In-Reply-To: <CAD44qMU6-GUDy%2BTUJ1Ndtcy7S42BCeSsFis0dMtj9LDOeDLwGA@mail.gmail.com> References: <20130220142140.f8e5a616c75d72e2519dbc69@freebsd.org> <54C08D8E-4C5F-49AF-BEE6-D78EC05D2A24@bsdimp.com> <CAD44qMXkFH9iR=ym1XBtD88HRadpGkO=WRYvz5xhAVucEuoLEA@mail.gmail.com> <20130220174449.GB6976@cicely7.cicely.de> <CAD44qMXsdrhuNRbpA1a9ikj4BGffVfhv1WY6hsqCxHwVzQAdsg@mail.gmail.com> <20130221022655.6f693eb6.ray@freebsd.org> <20130221014433.GA12189@cicely7.cicely.de> <20130221163026.dbeb03f9c38de3d24a7ab30f@freebsd.org> <CAD44qMU6-GUDy%2BTUJ1Ndtcy7S42BCeSsFis0dMtj9LDOeDLwGA@mail.gmail.com>
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On Thu, Feb 21, 2013 at 10:21:00AM -0500, Patrick Kelsey wrote: > >On Thu, Feb 21, 2013 at 9:30 AM, Aleksandr Rybalko <ray@freebsd.org> wrote: > >> On Thu, 21 Feb 2013 02:44:33 +0100 > >> Bernd Walter <ticso@cicely7.cicely.de> wrote: > >> > >> On Thu, Feb 21, 2013 at 02:26:55AM +0200, Aleksandr Rybalko wrote: > >> > 2. teach consumers to give only correct numbers (very nice we have only > >> > two SPI devices in tree) > >> > > >> > After that we will be able to make drivers for some (potential) devices > >> > which will require bidirectional communication. And controllers which > >> > can't do that, will just report error in that. I believe peoples thinks > >> > before attach such devices to controllers, so we will not have such > >> > incompatibility. > >> > >> I don't think there are many devices requiring RX/TX at the same time. > > > > Anyway, we will be able to do that, and we don't care now because don't > > have such drivers yet. > > > > Taking the view that "RX/TX at the same time" means that one wants to > send meaningful data to the slave device at the same time one is > interested in what data is returned during that transmission, there > are such devices in use out there. Linear Technologies has several > ADCs, such as the LTC2446, for which you obtain the previous > conversion result while sending the configuration bits for the next > conversion to be performed. Forgot about ADC with channel selection. > Although this is slightly out of focus for the specific issue > originally raised, while on the topic of things that need to get done > on SPI in real systems, there are also devices out there that require > specific data or some number of clocks to be provided while chip > select is deasserted. One example of the former is the LTC2404, which > is a multichannel ADC for which the input channel for the next > conversion is selected by the last four bits clocked in *before* chip > select is asserted. One example of the latter is the spec for SPI > access to MMC/SD cards, which requires a certain number of clocks to > be applied with chip select deasserted in order to initialize the > card. If you ever find yourself wondering why an SPI software > interface provides independent bus acquisition and chip select > control, the reason is to support these types of devices. With many ADC you also want probing support. Assign CS and GPIO-read MISO for ready without clocking. Some flash chips also work this way. Not sure if AT45DB support this and how our driver works. With own projects I usually ask AT45DB about ready state by transfering a status word. -- B.Walter <bernd@bwct.de> http://www.bwct.de Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.
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