Can't mux certain pins into mode 7

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1

Hi *,

I am currently writing some programs for the user space which help to
understand the whole muxing part.
There are certain pins which I cannot mux successfully, e.g. when I look at:
BONE:/sys/kernel/debug# cat gpio
GPIOs 0-31, gpio:
gpio-6 (mmc_cd ) in lo

GPIOs 32-63, gpio:
gpio-34 (sysfs ) out hi
gpio-35 (w1 ) in lo
gpio-38 (sysfs ) out hi
gpio-39 (sysfs ) out hi
gpio-53 (beaglebone::usr0 ) out lo
gpio-54 (beaglebone::usr1 ) out lo
gpio-55 (beaglebone::usr2 ) out lo
gpio-56 (beaglebone::usr3 ) out lo

GPIOs 64-95, gpio:
gpio-66 (sysfs ) out hi
gpio-67 (sysfs ) out hi

There is gpio_35 (aka GPIO1_3, aka P8_6) on the beaglebone. The above
output seems to tell me that another user "w1" claims the pin. The
others were hopefully all muxed córrectly by me. My guess is, that
some of the pins are reserved, e.g. I cannot simply do what I want
from userspace. My questions:
- who or what is "w1"?
- how can I find out more about who claims certain pins?
- where could I find out more about particular functions of pins, such
as gpmc_ad3, mmc1_dat6... So far I more or less learned by
coincidence that uart pins are for serial communication and ain pins
are my analog inputs.

I have to admit that the processor technical reference is a bit too
much for my current state of knowlegde.

Oh, while being at it -
how much can the GPIO pins sink or source? In some discussion about
the beagleboard it was mentioned per pin 8mA. Is that applicable to
the beaglebone too? Is there an upper total limit?

Thank you very much,
Markus

2

I have exactly the same problem with this pin. My understanding is that some higher priority job is claiming that pin and therefore we can’t use it from userspace. Please post your solution here when you find it.

3

It’s the 1-wire (http://en.wikipedia.org/wiki/1-Wire) driver that’s built into the kernel. If it’s super important to have that pin you can build a new kernel that doesn’t include that driver.

Steve

4

Thank you Steve!
Now that I know what it is (I also know 1-wire), how do know that it
is that? How could I have found out myself? Is there any kind of
procedure which connects "w1" to something else? How do I go from
where I am to what I know now?

I am just asking because like tomorrow, the will be something
"ZippyOne" and again I would not know how to know more.
Markus

5

Oh! In fact once one knows a bit, googling "w1 gpio" turns up all the
desired results.
Markus