Quick Reference

TODO: {{#todo:Keep Adding More (11.25.13-17:30->KY+);(11.26.13-21:25->MD+)|Klint Youngmeyer|oe 4,oe 5,ky,FinalDraft,md}}

This page is a quick reference guide or a "cheatsheet" to assist with the initial learning curve. Once full familiarity with the development environment is established, this quick reference will likely no longer be needed.

Working With the Terminal

Use minicom to bring up a serial terminal. To configure the serial console, run sudo minicom -s. The settings needed for configuring minicom can be found on this page. Select, Save as dfl, to save the settings you have configured to be the default settings whenever you run minicom. Use minicom -o to start minicom more quickly; the -o option tells minicom to start without sending AT commands to initialize a modem.

Editing a File

EMAC OE provides simple text editing capabilities for making changes to configuration files and scripts. Major editing tasks should be performed on a desktop system first, copying the desired files back to the target board. There are two text editors available on standard EMAC OE builds: vi and nano. vi is a very common text editor available on almost every Unix-like OS. nano is a more conventional text editor that can be easier to use for those not familiar with vi.

To edit a file with vi, run the command:

root@emac-oe:~# vi <filename>

To edit a file with nano, run the command:

root@emac-oe:~# nano <filename>

For a more detailed overview, see this page

Making Changes To The Target Machine's Fileystem

By default, the flash filesystem on most EMAC devices is mounted read-only. To make changes to the filesystem, it will have to be remounted as read-write. This can be done with the following command:

root@emac-oe:~# mount -o remount,rw /

To mount the filesystem as read-only again (without rebooting), type:

root@emac-oe:~# mount -o remount,ro /

Mounting a Flash Filesystem

SINCE THIS IS A QUICK REFERENCE DOCUMENT, THIS SECTION SHOULD PROBABLY BE SPLIT OFF INTO ITS OWN PAGE. The gist of how to do this could then be shown here, with a link to the separate document for more in-depth info.

There are four steps to mounting a flash filesystem on our EMAC OE machine:

1. Determine which device node is assigned to the flash device.

2. Determine which partition to mount.

3. Determine where to mount the device.

4. Mount the device.

Determining the Device Node Assigned to the Flash Device

The easiest way to determine which device node is assigned to a particular flash device is to inspect the output of the dmesg command shortly after the device has been connected to your machine. Follow these steps to do so:

1. Insert the SD, CF or microSD card or plug in the USB flash device to your EMAC OE machine.

2. Wait a few seconds for the device to settle and be recognized by the OS.

3. Run this command at at shell on your EMAC OE machine:
   

   root@emac-oe:~# dmesg | tail -n 15
   

4. Inspect the output. The output should look similar to the following:

   usb 2-2: new full speed USB device using at91_ohci and address 2
   usb 2-2: not running at top speed; connect to a high speed hub
   usb 2-2: configuration #1 chosen from 1 choice
   scsi0 : SCSI emulation for USB Mass Storage devices
   usb-storage: device found at 2
   usb-storage: waiting for device to settle before scanning
   scsi 0:0:0:0: Direct-Access              Patriot Memory   PMAP PQ: 0 ANSI: 4
   usb-storage: device scan complete
   sd 0:0:0:0: [sda] 15634432 512-byte hardware sectors: (8.00 GB/7.45 GiB)
   sd 0:0:0:0: [sda] Write Protect is off
   sd 0:0:0:0: [sda] Mode Sense: 23 00 00 00
   sd 0:0:0:0: [sda] Assuming drive cache: write through
   sd 0:0:0:0: [sda] Assuming drive cache: write through 
   sda: sda1
   sd 0:0:0:0: [sda] Attached SCSI removable disk
   

   Inside square brackets, we see sda. This is the root device node assigned to our flash device.

Determine Which Partition to Mount

On a line by itself, we see:

sda: sda1

This means one partition was found on our device: sda1. This is the partition we will use.

Determine Where to Mount the Device

Now that we know what device node we are going to mount, we need to determine where to mount it. The /mnt directory is typically used for this (mnt is short for mount).

Create a directory to use for the mountpoint:

root@emac-oe:~# mkdir /mnt/myflash

Alternatively, you can pick another place in the filesystem to use. Just make sure you have permission to create a directory in that location. If the directory contains files, it will still be used as the mountpoint when the mount command is issued; however, the files contained in the directory will be hidden for as long as the directory is in use as a mountpoint. This could create a great deal of confusion, so beware this potential pitfall.

Mount the Device

Now that sda1 has been determined to be the partition to mount and /mnt/myflash has been created to be used as the mountpoint, we can mount our flash device with the following command:

root@emac-oe:~# mount /dev/sda1 /mnt/myflash

If no message is returned from the above command, then it succeeded. To verify this, try the following command

root@emac-oe:~# mount | grep sda1

You should see your device listed in the output of the above command. If it is listed more than once, it may have been mounted automatically by the OS. If so, inspection of the output should show you where it was mounted.

Unmounting the Filesystem After Use

After you are finished using the flash device, you may wish to unmount it (similar to "Safely Removing" a device on other operating systems). The umount command is used for this purpose.

Continuing on with the example above, the device mounted above would be unmounted with the following command:

root@emac-oe:~# umount /mnt/myflash

If it was automounted elsewhere, it will also need to be unmounted from that mountpoint before it will be safe to remove the device. For instance, if the automounter mounted it on /media/sda1, then issue the following command:

root@emac-oe:~# umount /media/sda1

Network Interfaces

The ifup and ifdown commands may be used to enable (or, respectively, disable) network interfaces based on interface definitions in the file /etc/network/interfaces.

An example of using the ifup command:

root@emac-oe:~# ifup eth0

An example of using the ifdown command:

root@emac-oe:~# ifdown eth0

To temporarily configure the eth0 interface to have a static IP address, 192.168.1.125, to use a DNS server at 192.168.1.25, and to use a gateway at 192.168.1.1:

root@emac-oe:~# ifconfig eth0 up 192.168.1.125 netmask 255.255.255.0
root@emac-oe:~# route add default gw 192.168.1.1
root@emac-oe:~# echo "nameserver 192.168.1.25" > /etc/resolv.conf

Remote Access

To access an EMAC product remotely, it is easiest to use ssh and scp for remote command execution and remote file transfer respectively.

To log into a system with the IP address 10.0.2.41, enter the following command:

developer@ldc:~# ssh root@10.0.2.41

To execute a command on a remote system without opening a shell on the remote system (in this example, ls -la):

developer@ldc:~# ssh root@10.0.2.41 'ls -la'

To send the file example.text to the /home directory of a system with the IP address 10.0.2.41, enter the following command:

developer@ldc:~# scp example.text root@10.0.2.41:/home

Running a User Program

When a user program is uploaded, sometimes it does not have execute permissions. Use the following steps to ensure that your program functions properly.

1. Navigate to the directory that the application was uploaded to (e.g. /tmp):

   root@emac-oe~:$ cd /tmp
   

2. Make the application file executable:

   root@emac-oe~:$ chmod u+x <filename>
   

3. Run the application:

   root@emac-oe~:$ ./<filename>
   

See Also

• Getting Started with Linux
• Open Source Community