Network Management: Embedded Systems: Raspberry Pi Primer

Monday, February 1, 2016

Embedded Systems: Raspberry Pi Primer

[Raspberry Pi Model B, Courtesy RaspberryPi.org ]

Abstract:

Computers originated as systems the size of large rooms filled with vacuum tubes with massive heat dissipation and equipment failure issues. Over time, the creation of the transistor and it's replacement of tubes created cooler systems requiring less power and more robust reliability. The creation of the Silicon Chip enabled the consolidation of many transistors onto tiny surfaces. Techniques to merge more parts onto a single piece of silicon created the concept of a Single Board Computer, to the point where the best of these computers can reside mostly on a single chip. The Raspberry Pi is one example of this.

[Solaris Logo, Courtesy Sun Microsystems]

Is Solaris Available?

No, unfortunately, Solaris is not available. There is an attempt to bring up Illumos under the Raspberry Pi, so people are only hoping that this will be finished quickly to provide an enterprise UNIX for the embedded platform.

[Raspbian Logo, courtesy Raspbian.org]

Where to Start

The Frequently Asked Questions list is very important for understanding the system. Acquire a fairly inexpensive but fully functional single board embedded system - used in this article is the Raspberry Pi model B, which includes 4 USB ports, an ethernet port, SD Card, 512MB of RAM, HDMI port, and some other ports. Download the Raspberry Pi supported Operating System called Raspbian. Raspbian is based upon the Debian flavor of the Linux Operating System. At the time of this writing, Jessie is the most recent release of Raspbian.

Preparing the Embedded System

An SD Card should be chosen, with high performance read and write cycles, 32 Gigabytes is a good size. The common OS images, like Raspbian, easily fits within 8 Gigabytes, but a larger card should be chosen, all the way up to 32 Gigabytes with the model chosen in this article. Instructions below will expand into the entire card. After imaging an SD Card with Raspbian, the card can be booted from the SD Card.

Attaching the Embedded System

After attaching the Raspberry Pi to USB Power, Ethernet Cable, and optionally an HDMI cable. Other optional connections can be a mouse and keyboard. In this case, an alternate computer system will be used in order to contact the embedded system over SSH.

Booting the Embedded System

When booting the card, it will automatically get an IP Address via DHCP from a local DSL or Cable Modem. The Raspberry Pi will also update the DNS on an AT&T DSL terminator. There is a Red power light, next to the SD Card slot which illuminates during the boot. With each disk access, the green light illuminates. As the Operating System comes up, the Link integrity lights appear on the Ethernet Port.

Testing Network Connectivity

From another local machine on the network, the embedded system can be contacted.

macosx/user$ ping -c 3 raspberrypi
PING raspberrypi.attlocal.net (192.168.1.94): 56 data bytes
64 bytes from 192.168.1.94: icmp_seq=0 ttl=64 time=5.453 ms
64 bytes from 192.168.1.94: icmp_seq=1 ttl=64 time=1.808 ms
64 bytes from 192.168.1.94: icmp_seq=2 ttl=64 time=3.614 ms

--- raspberrypi.attlocal.net ping statistics ---
3 packets transmitted, 3 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 1.808/3.625/5.453/1.488 ms

The DNS Name will be available whenever the device is connected to the local network.

Remote Control of the Embedded System

The Raspberry Pi can be contacted through Secure Shell. Once logging in, root permission can be acquired via sudo.

macosx/user$ ssh pi@raspberrypi
The authenticity of host 'raspberrypi (192.168.1.94)' can't be established.
RSA key fingerprint is d0:e7:3c:78:b6:58:c6:22:8e:fa:fe:30:7e:cd:8e:79.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'raspberrypi' (RSA) to the list of known hosts.
pi@raspberrypi's password: raspberry

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Sun Jan 24 01:37:07 2016 from unknown001cb3b2a5ec
pi@raspberrypi:~ $ sudo bash
root@raspberrypi:/home/pi#

From the root based shell account, all updates can be conducted.

First Time Configuration

There are a variety of different options to adjust on the hardware configuration, which can be done through the command line.
root@raspberrypi:/home/pi# raspi-config

A Character based User Interface appears, with various capabilities. It is best viewed with a terminal window of 112 characters wide or larger.
┌─────────────────────┤ Raspberry Pi Software Configuration Tool (raspi-config) ├─────────────────────┐
│ │
│ 1 Expand Filesystem Ensures that all of the SD card storage is available to the OS │
│ 2 Change User Password Change password for the default user (pi) │
│ 3 Boot Options Choose whether to boot into a desktop environment or the command line│
│ 4 Wait for Network at Boot Choose whether to wait for network connection during boot │
│ 5 Internationalisation Options Set up language and regional settings to match your location │
│ 6 Enable Camera Enable this Pi to work with the Raspberry Pi Camera │
│ 7 Add to Rastrack Add this Pi to the online Raspberry Pi Map (Rastrack) │
│ 8 Overclock Configure overclocking for your Pi │
│ 9 Advanced Options Configure advanced settings │
│ 0 About raspi-config Information about this configuration tool │
│ │
└─────────────────────────────────────────────────────────────────────────────────────────────────────┘

Various steps should be taken to prepare the system during first time usage.

Expanding Root Filesystem

By default, the boot image is designed to fit on a 4 GB SD card. Larger SD cards are available and common, so increasing the size of the SD card through the config menu is the first order.

Selecting "1 Expand Filesystem" and Enter reminds the user that a reboot is needed to activate.

┌──────────────────────────────────────────────────────┐
│ │
│ Root partition has been resized. │
│ The filesystem will be enlarged upon the next reboot │
│ │
└──────────────────────────────────────────────────────┘

Pressing Enter again will select Ok and return to the menu

In the above example, the root file system was expanded into a 32 Gig card. The following is reported onto the terminal window, behind the Character Based User Interface.
Welcome to fdisk (util-linux 2.25.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Command (m for help): Disk /dev/mmcblk0: 29 GiB, 31167873024 bytes, 60874752 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xea0e7380

Device Boot Start End Sectors Size Id Type
/dev/mmcblk0p1 8192 131071 122880 60M c W95 FAT32 (LBA)
/dev/mmcblk0p2 131072 7684095 7553024 3.6G 83 Linux

Command (m for help): Partition number (1,2, default 2):
Partition 2 has been deleted.

Command (m for help): Partition type
p primary (1 primary, 0 extended, 3 free)
e extended (container for logical partitions)
Select (default p): Partition number (2-4, default 2): First sector (2048-60874751, default 2048): Last sector, +sectors or +size{K,M,G,T,P} (131072-60874751, default 60874751):
Created a new partition 2 of type 'Linux' and of size 29 GiB.

Command (m for help): Disk /dev/mmcblk0: 29 GiB, 31167873024 bytes, 60874752 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xea0e7380

Device Boot Start End Sectors Size Id Type
/dev/mmcblk0p1 8192 131071 122880 60M c W95 FAT32 (LBA)
/dev/mmcblk0p2 131072 60874751 60743680 29G 83 Linux

Command (m for help): The partition table has been altered.
Calling ioctl() to re-read partition table.
Re-reading the partition table failed.: Device or resource busy

The kernel still uses the old table. The new table will be used at the next reboot or after you run partprobe(8) or kpartx(8).

The next reboot will facilitate the larger root slice.

Updating Configuration Tool

The Raspberry Pi Configuration Tool should also be updated, while still in the Character Based User Interface.

Selected the "9 Advanced Options" brings the user to a menu where the updating the tool to the latest version can be conducted.

┌──────────────────┤ Raspberry Pi Software Configuration Tool (raspi-config) ├──────────────────┐

│ │

│ A1 Overscan You may need to configure overscan if black bars are present on display │

│ A2 Hostname Set the visible name for this Pi on a network │

│ A3 Memory Split Change the amount of memory made available to the GPU │

│ A4 SSH Enable/Disable remote command line access to your Pi using SSH │

│ A5 Device Tree Enable/Disable the use of Device Tree │

│ A6 SPI Enable/Disable automatic loading of SPI kernel module (needed for e.g. PiFace)│

│ A7 I2C Enable/Disable automatic loading of I2C kernel module │

│ A8 Serial Enable/Disable shell and kernel messages on the serial connection │

│ A9 Audio Force audio out through HDMI or 3.5mm jack │

│ A0 Update Update this tool to the latest version │

│ │

└───────────────────────────────────────────────────────────────────────────────────────────────┘

The Character Based User Interface briefly switches to the screen to show what is happening

Get:1 http://archive.raspberrypi.org jessie InRelease [13.4 kB]

Get:2 http://mirrordirector.raspbian.org jessie InRelease [15.0 kB]

Get:3 http://archive.raspberrypi.org jessie/main armhf Packages [109 kB]

Get:4 http://mirrordirector.raspbian.org jessie/main armhf Packages [8,963 kB]

Get:5 http://archive.raspberrypi.org jessie/ui armhf Packages [7,639 B]

Ign http://archive.raspberrypi.org jessie/main Translation-en_GB

Ign http://archive.raspberrypi.org jessie/main Translation-en

Ign http://archive.raspberrypi.org jessie/ui Translation-en_GB

Ign http://archive.raspberrypi.org jessie/ui Translation-en

Get:6 http://mirrordirector.raspbian.org jessie/contrib armhf Packages [37.5 kB]

Get:7 http://mirrordirector.raspbian.org jessie/non-free armhf Packages [70.3 kB]

Get:8 http://mirrordirector.raspbian.org jessie/rpi armhf Packages [1,356 B]

Ign http://mirrordirector.raspbian.org jessie/contrib Translation-en_GB

Ign http://mirrordirector.raspbian.org jessie/contrib Translation-en

Ign http://mirrordirector.raspbian.org jessie/main Translation-en_GB

Ign http://mirrordirector.raspbian.org jessie/main Translation-en

Ign http://mirrordirector.raspbian.org jessie/non-free Translation-en_GB

Ign http://mirrordirector.raspbian.org jessie/non-free Translation-en

Ign http://mirrordirector.raspbian.org jessie/rpi Translation-en_GB

Ign http://mirrordirector.raspbian.org jessie/rpi Translation-en

Fetched 9,217 kB in 41s (222 kB/s)

Reading package lists... Done

Building dependency tree

Reading state information... Done

The following packages will be upgraded:

raspi-config

1 upgraded, 0 newly installed, 0 to remove and 71 not upgraded.

Need to get 13.4 kB of archives.

After this operation, 0 B of additional disk space will be used.

Get:1 http://archive.raspberrypi.org/debian/ jessie/main raspi-config all 20160108 [13.4 kB]

Fetched 13.4 kB in 0s (31.0 kB/s)

(Reading database ... 123536 files and directories currently installed.)

Preparing to unpack .../raspi-config_20160108_all.deb ...

Unpacking raspi-config (20160108) over (20151117) ...

Processing triggers for systemd (215-17+deb8u2) ...

Setting up raspi-config (20160108) ...

The Raspberry Pi Software Configuration Tool has been updated.

Verify Root Resize via Exit and Restart

The user should Tab Twice to the Back option and hit Enter to exit the Advanced Menu, tab twice to the Finish option and hit Enter to exit the Character Based User Interface.

At this point, verification of the root slice resize can be done, first checking the existing size:

root@raspberrypi:/home/pi# df -h /

Filesystem Size Used Avail Use% Mounted on

/dev/root 3.5G 3.2G 96M 98% /

Force a restart of the embedded system:

root@raspberrypi:/home/pi# cd / ; sync ; init 6

Connection to raspberrypi closed by remote host.

Connection to raspberrypi closed.

Wait for Embedded System to become available:

macosx/user$ ping -c 1 raspberrypi

PING raspberrypi.attlocal.net (192.168.1.94): 56 data bytes

64 bytes from 192.168.1.94: icmp_seq=0 ttl=64 time=1.558 ms

--- raspberrypi.attlocal.net ping statistics ---

1 packets transmitted, 1 packets received, 0.0% packet loss

round-trip min/avg/max/stddev = 1.558/1.558/1.558/0.000 ms

Log back into system:

macosx/user$ ssh pi@raspberrypi

pi@raspberrypi's password: raspberry

The programs included with the Debian GNU/Linux system are free software;

the exact distribution terms for each program are described in the

individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent

permitted by applicable law.

Last login: Sun Jan 24 05:48:43 2016

Note the larger available root space

pi@raspberrypi:~ $ df -h /

Filesystem Size Used Avail Use% Mounted on

/dev/root 29G 3.2G 25G 12% /

The SD Card now has 29 Gigabytes of usable space.

[Chocolate Packaging, courtesy jayce-o.blogspot.com ]

Update Debian Packaging Repository

With extra storage, the packaging system repository should now be updated, as root.

pi@raspberrypi:~ $ sudo bash

root@raspberrypi:/home/pi# apt-get update

Hit http://archive.raspberrypi.org jessie InRelease

Hit http://mirrordirector.raspbian.org jessie InRelease

Hit http://archive.raspberrypi.org jessie/main armhf Packages

Hit http://mirrordirector.raspbian.org jessie/main armhf Packages

Hit http://archive.raspberrypi.org jessie/ui armhf Packages

Hit http://mirrordirector.raspbian.org jessie/contrib armhf Packages

Hit http://mirrordirector.raspbian.org jessie/non-free armhf Packages

Hit http://mirrordirector.raspbian.org jessie/rpi armhf Packages