ASEE 2013 Workshop

Here are the labs for the afternoon Linux part of the ASEE 2013 Workshop

Warm Up
Before we can interact with LEDs and switches we need to learn some simple Linux commands.
 * 1) On your host computer, running Windows, start up puTTY.
 * 2) If you get a Security Warning, click Run.
 * 3) Enter 192.167.7.2 in the Host Name field and click Open
 * 4) Login as root with no password.
 * 5) Enter ls  to list what files you have. You shouldn't see much.

At this point you need to learn a few simple Linux commands for creating and displaying files. Once you know these commands it's easy to turn an LED on and off.

First, let's edit a file using the nano editor. Nano is a simple editor that easy to learn. This will edit (and create) the file play.

bone$ nano play

Add a couple of lines of text to the file, it doesn't really matter what and then Exit. You can list the files in the current directory with ls and show the contents of a file with cat. bone$ ls Desktop play bone$ cat play A couple of lines of text.

Use echo to print a line of text. bone$ echo This is a line of text This is a line of text

Here's a powerful operator. You can take the output of any command and redirect it to a file with >.

bone$ echo This is a line of text > here bone$ cat here This is a line of text

We are almost there. Use cd to change directories. / is the top level directory. bone$ cd / bone$ ls bin  dev  home  lost+found  mnt   run   sys  usr boot etc  lib   media       proc  sbin  tmp  var

If you ever get lost, cd alone takes you home. bone$ cd gone$ ls Desktop here  play

Now you are ready to flash an LED.

gpio via the Shell Command Line and sysfs
The easiest way to do general purpose I/O (gpio) on the Beagle is through a terminal window and a shell prompt. In Linux, almost everything is treated as a file, even things that aren't files. In our class we'll use a virtual file system called sysfs. sysfs exposes the drivers for the hardware so you get easily use them.

Try this: bone$ cd /sys bone$ ls -F block/ bus/  class/  dev/  devices/  firmware/  fs/  kernel/  module/  power/

Here we see several directories that represent hardware we can control. Explore a bit and see what you find.

Now try:

beagle$ cd /sys/class beagle$ ls -F backlight/ firmware/     lcd/       mtd/           scsi_disk/   ubi/ bdi/       gpio/         leds/      net/           scsi_host/   udc/ block/     graphics/     mbox/      power_supply/  sound/       uio/ bluetooth/ hwmon/        mdio_bus/  regulator/     spi_master/  usbmon/ bsg/       i2c-adapter/  mem/       rfkill/        spidev/      vc/ dma/       i2c-dev/      misc/      rtc/           thermal/     vtconsole/ drm/       input/        mmc_host/  scsi_device/   tty/         watchdog/

Explore some.

Blinking a USR LED
The Beagle Black has four user LEDS, user0 - user3, that you can control. Try this:

bone$ cd /sys/class/leds bone$ ls -F beaglebone:green:usr0 beaglebone:green:usr2 beaglebone:green:usr1 beaglebone:green:usr3

Here you see the directories for controlling each of the usr LEDs. By default, usr0 flashes a heartbeat pattern and usr1 flashes when the micro SD card is accessed. Let's control usr0.

bone$ cd beagleboard\:\:usr0 bone$ ls -F brightness device@  max_brightness  power/  subsystem@  trigger  uevent

See what's in brightness, max_brightness and trigger by using the  command. For example:

bone$ cat trigger none nand-disk mmc0 timer oneshot [heartbeat] backlight gpio cpu0 default-on transient

This shows trigger can have many values. The present value is heartbeat. Check the LED, is it beating? You can stop the heartbeat via:

bone$ echo none > trigger bone$ cat trigger [none] nand-disk mmc0 timer oneshot heartbeat backlight gpio cpu0 default-on transient

Did it stop beating? You can now turn it on and off with:

bone$ echo 1 > brightness bone$ echo 0 > brightness

Is it responding correctly?

The Bone has more trigger options. Try:

bone$ cat trigger [none] mmc0 timer heartbeat backlight gpio default-on bone$ echo timer > trigger bone$ ls -F brightness delay_on  max_brightness  subsystem@  uevent delay_off  device@   power/          trigger bone$ echo 100 > delay_on bone$ echo 900 > delay_off

What does this do?

Blinking an External LED via gpio
In the AM lab we wired an LED to the P9_12 General Purpose IO (gpio) port and controlled it via BoneScript. Here we'll control it via a shell command. First we need to figure out which gpio pin P9_12 is attached to. The following figure shows it attached to gpio_60.



Here's how you turn it on

bone$ cd /sys/class/gpio bone$ ls -F export gpiochip0@  gpiochip32@  gpiochip64@  gpiochip96@  unexport

Presently no gpio pins are visible. You need to tell it which pin to export

bone$ echo 60 > export bone$ ls -F export gpio60@  gpiochip0@  gpiochip32@  gpiochip64@  gpiochip96@  unexport

Notice gpio60 has appeared. All we need to do is tell it which direction and then turn it on.

bone$ cd gpio60 bone$ echo out > direction bone$ echo 1 > value

Your LED should be on! When you are done you can unexport the pin and it will disappear. bone$ cd .. bone$ echo 60 > unexport