[PATCH] SPI: BCM2835: enable support of 3-wire mode
pigpio at abyz.co.uk
Fri Mar 20 06:38:15 PDT 2015
Not sure what you guys are saying.
On Fri, 2015-03-20 at 07:17 +0100, Martin Sperl wrote:
> > On 20.03.2015, at 06:12, Stephen Warren <swarren at wwwdotorg.org> wrote:
> > I can see how that tells the HW which direction to transfer data in
> > 3WIRE mode, but how does the HW know whether it's in 3WIRE mode or has
> > separate RX/TX lines?
> The HW assumes with this flag that MISO (=RX) sits on the same physical
> line as MOSI (=TX). This flag essentially just changes directions of
> the TX GPIO pin from out to in and samples the level on the TX pin.
> Without this patch what you would need to do to make such a device
> work is connecting RX with TX and that with the MIMO pin of the final
> device (maybe add a pullup). This flag is essentially just a shortcut.
> Note that the SPI-framework does the testing so that either RX or TX
> can be set in SPI-3WIRE mode (not both).
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