Half-duplex SPI using single data wire

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1

Hello,

I want to connect to my beaglebone an LCD display which uses a 3-wire
SPI interface: communication in both directions (to and from device)
is implemented using only CS, SCK and a single data wire. The data
wire is used in half-duplex mode, with direction switched depending
whether write or read operation is expected. The SRM says that the SPI
interface in the processor supports this mode, but how can I control
the direction of the data line from user-space program? Since I can't
control pinmuxing, changing pin direction is not possible. Will it be
enough just to flip the bit in OE register?

Thx,
j.

2

plz follow this guide http://communistcode.co.uk/blog/blogPost.php?blogPostID=1

I have made various devices working.

3

Thanks. But this tutorial only shows how to enable SPI in 3.2 kernel.
I have 4-wire SPI working, I need to configure it in 3-wire mode.

j.

4

I found in device tree docs SPI property "spi-3wire" which does
exactly what I need, but I can't find in spi-omap2-mcspi.c any
references to this mode. Has anybody tried to use SPI in 3-wire mode?
Did it work?

thx,
j.

5

Hi Jacek,

How did you resolve the 3-wire issue with beagle ?
I don’t se ethat the driver supports 3-wire.

Regards,
Ran