Configuring Pins Mode Beaglebone

Question

In the beagleboard or beaglebone are different modes to work the pin. With the previous kernel they are located in /sys/kernel/debug/omap_mux. Do u know with the last Kernel where are those files?

Answer 1

I found many of the examples provided at hipstercircuits to be a bit overwhelming; especially if you're just looking to adjust the pins to mode 7. If anyone reading this is having the same issue, the following link may help: http://bbbadventures.blogspot.ca/2013/06/pinmuxing.html It provides the most basic template.

Should the link above break, here's the snippet provided (with a few tweaks for clarity):

/*
* Copyright (C) 2012 Texas Instruments Incorporated - http://www.ti.com/
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
/dts-v1/;
/plugin/;

/ { compatible = "ti,beaglebone", "ti,beaglebone-black";
    /* identification */
    part-number = "pinctrl-test-0";
    fragment@0 {
        target = <&am33xx_pinmux>;
        __overlay__ {
            pinctrl_test: pinctrl_test_0_pins {
                pinctrl-single,pins = <
                    0x030 0x07 /* P8_12 OUTPUT | MODE7 */
                    0x034 0x07 /* P8_11 OUTPUT | MODE7 */
                    /* Add more pins here */
                >;
            };
        };
    };

    fragment@1 {
        target = <&ocp>;
        __overlay__ {
            test_helper: helper {
                compatible = "bone-pinmux-helper";
                pinctrl-names = "default";
                pinctrl-0 = <&pinctrl_test>;
                status = "okay";
            };
        };
    };
};

When adding more pins to the above snippet, you can use the following tables to identify which hex values match the pins:

• https://github.com/derekmolloy/boneDeviceTree/blob/master/docs/BeagleboneBlackP8HeaderTable.pdf?raw=true
• https://github.com/derekmolloy/boneDeviceTree/blob/master/docs/BeagleboneBlackP9HeaderTable.pdf?raw=true

Each pin is set by appending an additional entry into pinctrl-single,pins. The format looks like this:

[offset] [mode]

Example: 0x030 0x07

In the two tables linked above refer to the third column, entitled "ADDR/OFFSET", for the offset value.

I hope this helps :)

Edit: I should also mention that the answers provided by Martin and Don are both excellent should help cover the rest of the important details.

Answer 2

Don Branson's answer is a great introduction on how to read GPIO pins, but unfortunately it does not cover how you can change a pin's mode, e.g. from GPIO to SPI. This became more complicated with kernels 3.8.13 (?) and up. For a number of reasons, the kernel developers switched to the "device tree model".

As of now, the details on how to use the device-tree-models seem to be in flux, so I will only describe the general process. You start out by describing the pins that you want to interact with in a file called "device tree source". The pins and their modes are specified using hexadecimals numbers that you have to look up in the documentation of the processor.

You then compile this file using dtc into a "device tree binary" and place this binary into /lib/firmware. Finally, you enable the pin modes by echoing the name of the binary file (you can omit the .dtb extension) to /sys/devices/bone_capemgr.*/slots.

A very informative example is layed out in this great blogpost:

http://hipstercircuits.com/enable-spi-with-device-tree-on-beaglebone-black-copy-paste/

I will try to expand my answer as I learn more about this topic myself. Or maybe someone can suggest edits or hopefully even a more expansive answer of their own? The information that is currently available seems to be a bit sparse...

The best of luck to you!

Answer 3

I found what I needed here: http://www.armhf.com/index.php/using-beaglebone-black-gpios/.

I'm running kernel 3.8.13.

Based on that, I wrote this script:

#!/bin/bash

# http://www.armhf.com/index.php/using-beaglebone-black-gpios/
# pin 9:11, gpio0[30] - 0 + 30 = 30
echo 30 > /sys/class/gpio/export
echo in > /sys/class/gpio/gpio30/direction
cat /sys/class/gpio/gpio30/value

# 1=switch open; 0=switch closed
while [ 1 ] ; do cat /sys/class/gpio/gpio30/value ; sleep .5 ; done

When the pin is held low, the script displays 0, and 1 when high. I breadboarded a circuit based on http://www.digikey.com/us/en/techzone/microcontroller/resources/articles/protecting-inputs-in-digital-electronics.html.

The orange wires on the right side of the pic act as a switch.

My plan is to then take this and a door switch from a dead printer to make a freezer switch. Then I'll modify the script to email me when the freezer's been open for more than say, 10 minutes.

Edit:

Did some study and found more info on how to set pinmux, specifically with device tree overlays:

Okay, watched this, and learned a lot: http://www.youtube.com/watch?v=wui_wU1AeQc

Was able to finally get control over pinmux settings on the BBB with the device tree overlay below. The fragment@1 section is still magic to me, so at some point hopefully it'll make more sense. Nevertheless, at least I can detect closed switches on all for pins.

One critical piece was the chart in Derek's project here: https://github.com/derekmolloy/boneDeviceTree/tree/master/docs

/dts-v1/;
/plugin/;

/ {
        compatible = "ti,beaglebone", "ti,beaglebone-black";
        part-number = "mousetraps";
        version = "00A1";

        /* https://github.com/derekmolloy/boneDeviceTree/blob/master/docs/BeagleboneBlackP9HeaderTable.pdf */
        fragment@0{
                target = <&am33xx_pinmux>;
                __overlay__ {
                        mousetrap_pins: pinmux_mousetrap_pins {
                            pinctrl-single,pins = <
                                    0x070 0x2f /* P9_11 30 INPUT MODE7 none */
                                    0x074 0x2f /* P9_13 31 INPUT MODE7 none */
                                    0x040 0x2f /* P9_15 48 INPUT MODE7 none */
                                    0x15c 0x2f /* P9_17 05 INPUT MODE7 none */
                            >;
                        };
                };
        };

        fragment@1{
                target = <&ocp>;
                __overlay__ {
                        test_helper: helper {
                                compatible = "bone-pinmux-helper";
                                pinctrl-names = "default";
                                pinctrl-0 = <&mousetrap_pins>;
                                status = "okay";
                        };
                };
        };
};