[MinnowBoard] GPIO – blocked GPIO request

[John Hawley]

Only way I can think of to do would be from inside the kernel directly,
as I don't think the registers for the GPIOs are exposed up through user
space.  Worst case you can just go and read/write to the memory
directly, but that always comes with the associated risks.

You'll also note that there are 3 GPIO controllers on the MinnowBoard
MAX / Turbot, encompassing 255 potential GPIOs.  The pins were mainly
picked for their native (non-gpio) functionality, and as a result may
not be anywhere near each other from a register perspective.

For example pins 21,23,25 are on a different controller than the rest of
the pins in the LSE.

	LSE Pins 21,23,25 are on
		GPIOs 82-125, platform/INT33FC:02, INT33FC:02:

	Rest of the LSE Pins are on
		GPIOs 154-255, platform/INT33FC:00, INT33FC:00:

(noting the Linux GPIO numbering above is coming from a Linux 3.14
kernel, add 256 to those numbers if you are on anything 3.18 or newer)

If you aren't going through trying to toggle the lines simultaneously
like you are suggesting by reading / writing the registers directly,
it's going to come down to how quickly you need to toggle the lines for
the protocol you are working on, as there's usually a (small) window
where you can toggle things and have the hardware recognize it as being
within the window for being right.

- John

On 05/12/2016 07:26 AM, Abdelghani Ouchabane wrote:
> Hello,
>   is it possible to toggle values of several GPIO lines at the same
> time, such as a data and clock line.
> 
> "Since several GPIO lines are often handily placed in the same register,
> it is often actually possible to read or write 8, 16 or 32 GPIO lines at
> the same time. By attaching hardware to lines in the same register."
> 
> Thanks
> Ghani
> 
> This email has been scanned by Barracuda Networks.
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