Raspberry Pi

This Page is Dated

In the summer of 2012 I recieved our first Raspberry Pi. That first summer I explored the early model B that had 256MB of ram. These are my notes.

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I do not have a new location yet.

Initial Description

This is a single board ARM processor computer. It boots from an SD card. USB ports and an Ethernet LAN port are included. A number of expansion boards are in the works. These should allow one to connect to the real world. It is also possible to connect to the real world with a general purpose USB virtual serial port.

It has an HDMI output that can connect to a digital TV or monitor. A USB keyboard can be connected.

This is really modern looking as ARM is the sort of low power consumption processor used in tablets and smart phones including iPads iPhones and Androids.

There are different options for operating system. We will start off with Raspbian "wheezy" as this was the recommended downloadable image when our R-Pi arrived. (download page http://www.raspberrypi.org/downloads). Some background information can be found at http://www.raspbian.org/RaspbianAbout .

Photo of the Raspberry Pi connected to a monitor via the HDMI. Power, USB Keyboard and USB mouse also connected. When testing I also connected an ethernet LAN cable (not shown here). The ARM processor is actually under the RAM which can be seen at the center of the board
(for layout diagram see http://www.raspberrypi.org/wp-content/uploads/2011/11 /Raspi-Model-AB-Mono-1.png)

Background https://www.youtube.com/watch?v=u4THiC5-JZo

Other Handy information http://www.raspberrypi-spy.co.uk/

Table of Contents

Raspberry Pi Received (summer 2012)

The Raspberry Pi is here.

how 2. http://www.raspberrypi.org/downloads

The Raspbian SD card image was recently released so I decided to use it (see http://www.raspberrypi.org/archives/1605 -- Raspbian-based SD card image released). I found the instructions given in 1 and 2 above easy to follow. Some people live video demos. One has been posted here (http://www.youtube.com/watch?v=ZpBThpH4iuA).

I have plugged in our Raspberry Pi and so far everything seems to be working. The Raspbian-based SD image has a new setup tool called raspi-config. I stopped to checkout http://elinux.org/RPi_raspi-config to see if there is anything I want to configure before I do anything else.

Our First R-Pi is a Rev1 Board

There is a new revision 2.0 that will be shipping. Our first R-Pi is a revision 1 board. The differences are itemized at the following link:

Backing up SD Card

The tool recommended on the Raspberry Pi Downloads site

for windows users to get an linux image onto a SD card and also to back up SD cards is available here

It looks like this is still an early release of the tool and from what I read in the forums it does not always work with SD readers built into laptops. Fortunately when I tried it with our Dell Latitude laptop I was able to save the Rasbian image to the SD card with no issues.

After working with the R-Pi for many days I wanted to save an card image before making more changes. This did not work with the Dell Latitude. I did not get any error messages but ended up with a tiny 57 MB *.img file which could not be a proper image of a 8 GB SD card. After playing around with this for some time I decided to try it out on our newest Acer netbook. It worked perfectly and the new image file was just under 8 GB as expected.

Checking the Raspberry Pi Out

Setting Configuration

  1. I set this RPi to boot to the text login screen.
    The X window system is still available and can be started by simply typing startx. On GNU/Linux systems (and Unix) the graphical windows system is optional. When X is not used more memory is available for other tasks.

  2. Set the timezone

  3. expanded the root partition to fill the 8 GB SD Card.

  4. Set it to use US keyboard layout (the default is UK which clearly is different -- http://www.goodtyping.com/teclatUK.htm). In Canada (outside of Quebec) the US Keyboard is typical (http://www.cooltoyzph.com/image/US_Keyboard_layout.jpg).

Setting the Date and Time

The Raspberry Pi does not have a hardware real time clock. It looses the set time and date every time it is powered off. It can automatically get date and time off the internet. That works for me at home but in the lab on campus that service is not available so the time and date must be set manually.

Updating Wiki Using the RPi

This updadate to this page has been done on the Raspberry Pi itself. The Raspbian SD image ships with more than one browser.

Headless Local Login

ttyAMA0 UART

The ttyAMA0 UART provides a way to log on locally with the Raspberry pi headless. Jumpers were connected to ground, Tx and Rx.

Jumpers

ground    black
Tx        blue
Rx        green

CREATOR: gd-jpeg v1.0 klzzwxh:0017using IJG JPEG v62klzzwxh:0018, quality =
70 Here the other end of the jumpers connect to corresponding pins on a FTDI UART to USB converter (from Solarbotics) which connects to a Personal Computer. The other end of the jumpers could be connected to other interfaces. They could for example connect to a PIC board or a PIC on a solderless breadboard. The jumpers could be eliminated entirely if one used the Adafruit Pi Plate.

The Solarbotics FTDI board is easily modified for 3.3 volt operation. This modification involves cutting one hair line trace and adding a solder bridge to the underside of the FTDI board.

The end of the boot sequences messages looks as follows (as displayed in hyperterminal on a XP computer.).

...
[    4.872377] EXT4-fs (mmcblk0p2): mounted filesystem with ordered data mode. Opts: (null)
[    4.885483] VFS: Mounted root (ext4 filesystem) on device 179:2.
[    4.895629] Freeing init memory: 200K
[    4.952638] usb 1-1: new high speed USB device number 2 using dwc_otg
[    5.173196] usb 1-1: New USB device found, idVendor=0424, idProduct=9512
[    5.186067] usb 1-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0

[    5.199258] hub 1-1:1.0: USB hub found
[    5.207472] hub 1-1:1.0: 3 ports detected
[    5.492967] usb 1-1.1: new high speed USB device number 3 using dwc_otg
[    5.613317] usb 1-1.1: New USB device found, idVendor=0424, idProduct=ec00
[    5.627921] usb 1-1.1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
[    5.644377] smsc95xx v1.0.4
[    5.708429] smsc95xx 1-1.1:1.0: eth0: register 'smsc95xx' at usb-bcm2708_usb-1.1, smsc95xx USB 2.0 Ethernet, b8:27:eb:fc:b8:d1
[   20.976886] EXT4-fs (mmcblk0p2): re-mounted. Opts: (null)
[   21.338713] ### snd_bcm2835_alsa_probe c05d07a0 ############### PROBING FOR bcm2835 ALSA device (0):(1) ###############
[   21.354768] Creating card...
[   21.360206] Creating device/chip ..
[   21.366883] Adding controls ..
[   21.372375] Registering card ....
[   21.387371] bcm2835 ALSA CARD CREATED!
[   21.399343] ### BCM2835 ALSA driver init OK ###
[   29.089017] smsc95xx 1-1.1:1.0: eth0: link up, 100Mbps, full-duplex, lpa 0x45E1

Debian GNU/Linux wheezy/sid raspberrypi ttyAMA0

raspberrypi login:

Configuration for Command Shell or Other Uses

By default /dev/ttyAMA0 is set up to display the boot information and to allow login. This would be particularly useful for headless operation particularly if remote login via SSH goes down for some reason.

By default one would not be able to access this UART with programs like minicom since it is by default listening to input to the command shell. If desired the device configuration can be changed.

ttyAMA0 Configuration Reset

The ttyAMA0 interface has been reset for use by a user (meaning it is not longer at the default settings). This required changes to

  1. /etc/inittab

  2. /boot/cmdline.txt

See http://www.hobbytronics.co.uk/raspberry-pi-serial-port for the details.

This allows one to use minicom with the /dev/ttyAMA0 device.

This is a screen shot of what is seen in a remote command shell session. Note that the terminal mutiplexer tmux is being used so exactly the same session of minicom is visible at more than one remote computer.

In this case the PIC is not powered initially which results in some garbage being displayed as a result of noise received. As soon as the PIC is powered up a message is displayed. After this the Raspberry Pi passes on keystrokes to the PIC which will turn the LED on when it receives an "L" and off when it receives an "F".

Notes on PIC program and other details at rpi_pic_led.html

Remote Login

remote command line interface (CLI)

While it is possible to use the Raspberry Pi connected to a monitor (or HDMI TV), keyboard and mouse for us it would be great to have remote access most of the time. This can be done with a secure shell.

Notes

  1. when this diagram was drawn I had not yet reconfigured /dev/ttyAMA0 for general use. Once this is done the PIC can be connected directly to the Raspberry Pi (see ttyama0_configuration_reset)

  2. The connection to the USB to Serial FTDI board is more reliable when the Raspberry Pi is connected to a USB hub and the USB to Serial FTDI board is downstream of the hub.

The screen shot below shows a remote login. This time the Raspberry Pi was booted with no moitor, keyboard or mouse attached. I don't even have the cables or USB devices at home! What I do have at home is a router (with wi-fi and LAN connections) and a winXP computer as well as access to an Android tablet (the Raspberry Pi can be accessed by both the winXP computer and the tablet).

Remote Raspberry Pi X Desktop

It is also possible to get a remote desktop. More at

Example screen shot showing a remote Raspberry Pi X desktop window sitting on a windows XP desktop. It is also possible to remotely interact with the Raspberry Pi desktop on an Android device.

Creating Plots with matplotlib

New page at matplotlib.html with more details.

Screen Shot

A screen shot of how a matplotlib plot looks on the Raspberry Pi remote desktop is shown below. This is the screenshot with the remote Raspberry Pi desktop sitting on a windows XP desktop using the tightvnc viewer. This can also be viewed on an Android tablet using android-vnc-viewer

Also of interest

IPython on the Raspberry Pi

IPython will run on the Raspberry Pi. I have a new page to show screen shots:

Geany An IDE on the Raspberry Pi

I started to play with Geany. This is an IDE that can be used for C projects (and other languages) on the Raspberry Pi.

I started with a simple hello world program in C. There were no real surprises with this simple project. Geany worked like a typical IDE. Meaning I was able to create the project, create a simple c file, build the project and run the result from within the IDE.

More detail and screen shots at this link geany.html.

Terminal Multiplexer tmux

tmux02who.jpg The terminal multiplexer tmux allows one to access the same command shell session from more than one device. In this screen shot one can see a PuTTY window and a hyperterminal window. They are sharing a single tmux session so anything typed in one window shows up in all (not shown here the same shell is appearing on a remote Android device.

tmux01.jpg

In this session /dev/ttyAMA0 is connected to a Serial to USB adapter and PC running Hyperterminal. Alternatively /dev/ttyAMA0 could be connected to a PIC (running at 3.3 volts).

manual page for tmux

USB virtual Serial Port

Headless Raspberry Pi

FTDI FT232RL

The Raspberry Pi running Raspian "Wheezy" boots with a driver installed for FTDI FT232RL. A suitable board containing that IC and supporting parts is available from Solarbotics.

I have used this board in the past to connect a PC running windows to PIC projects. It works nicely plugged into the USB port of the Raspberry Pi (at least when loaded with Raspbian which is what I am using).

The dialout Group

In Linux systems a user login must be a member of the dialout group in order to use a tty device. At the command prompt a ID command allows one to determine which groups they belong to.

$ id
uid=1002(pic18lf2620) gid=1003(pic18lf2620) groups=1003(pic18lf2620),20(dialout)
$

If dialout does not appear in the list the user must be added to the dialout group. Instructions on added a user to a group appear here:

In Linux many users can be added. For testing the virtual USB device I used a new user called pic18lf2620 and did not add this user to the sudo group. This limits what can be done with the account.

Instructions regarding adding users can be found here:

ttyUSB0

When the TTLyFTDI USB-to-TTL Cable Adapter board is plugged into the Raspberry Pi USB port it can be accessed as /dev/ttyUSB0 A text file can be sent through the virtal serial port using a copy command at the command prompt.

$ cp textfile /dev/ttyUSB0

It is also possible to interact with the port using a terminal program. One simple terminal program that can be started from the CLI is minicom. This program is compatible with a secure shell.

Installing minicom

Instructions at

Raspberry PI (Rasbian) Using a USB Virtual Serial Port with PIC Projects

For anyone already used to doing projects with PIC MCU's a USB Virtual Serial Port provides a simple way to connect PIC project to the Raspberry Pi without concern about damage to the Raspberry Pi board. The FTDI board acts as a buffer as well as a USB to serial translator.

The TTLyFTDI USB-to-TTL Cable Adapter board from Solarbotics is automatically detected by a Raspberry Pi running Raspbian (the driver is pre-installed in the Raspbian image).

I will create new pages for new projects.

Pushing to a Remote FTP Server Using Python

The Raspberry Pi can interact with a PIC MCU to read sensor data and push it to a website.

Apache Web Server on Raspberry Pi

Followed the directions at

to install Apache web server on Raspberry Pi. It worked without any issues.

PHP Installed

Followed the directions at

I was able to sFTP a backup version the dokuwiki PHP package that runs this site to the Raspberry Pi. A screenshot is shown below.

Other Items Tested

Mounting USB drives

Followed directions at http://elinux.org/RPi_Adding_USB_Drives#Mounting_a_Partition I deviated from the instructions in that page in that no USB hub was used. Access to the flash drive is working.

Setting up Printer

Used procedure given at http://www.penguintutor.com/linux/printing-cups to set up printer.

Installed Lynx Text Only Web Browser

Installed Lynx text only web browser. It reminds me of the early days of the world wide web. It can be used with the remote raspbian command line interface. Lynx allows one to test what a web page looks like without images and ensure it can be navigated by web robots and screen reader systems. It is also possible to edit wiki pages (this paragraph was edited using Lynx running on the Raspberry Pi).

The screenshot shown above is from the Windows desktops.

To get Lynx to work with the Android tablet it was necessary to install an alternate keyboard. "Hackers Keyboard" Android application was installed. This virtual keyboard application works with ConnectBot as well. The default virtual keyboard lacks a Ctrl key and arrow keys that are needed for both lynx and ConnectBot.

For more on remote access see ssh.html.

Halting the Raspberry Pi

Use the following to halt the Raspberry Pi:

sudo shutdown -h now

You will be prompted for the su password. Then just type logout.

You should see all of the LED's turn off except the power LED. It is then safe to pull the power plug.

Rebooting the Raspberry Pi

sudo reboot

Expect the reboot to take some time. Progress can be watched on the LED's. When the Raspberry Pi has fully booted with a network cable attached the LED's will be on as follows

OK    off
PWR   on green
FDX   on green
LINK  on green may still flash a bit
10M   on green

Logging the IP address

I am generally using the Raspberry Pi headless (without a monitor and keyboard but with a network cable).

The lines that I added to rc.local all contain >> /home/danp/ip.log (danp is just the login username I am currently using). In the lab computers are consistently getting the same IP address from DHCP when they are switched on. There is no certainty the IP address assigned will always be the same address in the future but if it changes the new address will be logged. It would be handy to have a router on hand to make it easier to read the log if/when this should happen.

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#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

# Print the IP address
_IP=$(hostname -I) || true
if [ "$_IP" ]; then
  printf "My IP address is %s\n" "$_IP"   # the output from this line should appear near the end of all the
                                          # boot message if one is watching the boot-sequence with a monitor.
  printf "\tMy IP address is %s\n" "$_IP" >> /home/danp/ip.log  # appends the logfile
fi

date >> /home/danp/ip.log                  # these lines also print msgs at the end of the log file
printf "rc.local was modified by Dan Peirce B.Sc.\n" >> /home/danp/ip.log

exit 0

The log shows:

Two more Raspberry Pi's were received on October 4, 2012. A new log entry shows:

News

GPIO Connections

/dev/ttyAMA0 UART now tested and working with LED-PIC project see ttyama0_uart
Next step to read temperature sensor. Once I have some hardware as I want it I will hard wire it on a Protoyping Pi plate. For now I am using a breadboard.
Adafruit Prototyping Pi Plate Kit for Raspberry Pi. There is a review of this board and others at http://www.doctormonk.com.

RPi UART

How we Might Use the Raspberry Pi

I think we would continue using a PIC18F for interfacing to sensors, LED's and switches. We could then add the Raspberry Pi when we want to access the PIC18F from a PC. One can log into the R-Pi over a LAN using a secure shell. [There are many options for accessing the PIC from the R-Pi.

The Raspberry Pi is also capable of running a simple web server. It could act as a bridge between our PIC18f and the LAN.

The Raspberry Pi does have a serial port running at 3.3v (rather than RS-232 voltage levels). One should be able to connect a PIC also running at 3.3 volts directly to the Raspberry Pi serial port. (It may be significantly easier to do this with python. Something to look into).

Other uses might eventually present themselves but that alone would probably justify the cost.

Other Uses

Writing simple C programs

They were developed as computers for teaching programming. They come with Python installed for that purpose. Since they run Linux they also have a native c compiler. We would could connect to the Raspberry Pi's over the LAN using a remote login.

If the raspberry pi is used as a workstation with a monitor and keyboard one can use a graphical inte'grated development environment. If used with a remote command line interface one will only have command line tools. If nothing else using command line tools gives one some insight into how the C build process works.

Access to GPIO

More on GPIO at http://elinux.org/RPi_Low-level_peripherals I think for now I will avoid access to the gpio apart from the UART for which the kernel support exists and should stay stable in upcoming releases. The UART should be able to talk to a 3.3 V PIC USART without issues; however it would be expedient to have a buffer at the Raspberry Pi as a precaution.

Networking

In the old Electronics Technology program we used to use Linux boxes to teach networking. One limitation of this "computer" is that it only has one network port and we can't just plug in another one. There are things we could do with these.