Remote Desktop (2)

When running the remote desktop you are working on the Raspberry Pi

with the screen, keyboard and mouse replaced by the devices on the PC.

You have the same functionality as if the screen was connected

to the Pi’s HDMI port and keyboard and mouse were connected

to the USB ports on the Pi.

nfs the network file system

With nfs you can mount part of the Pi’s file system tree

onto your PC file system.

This allows you access to the Pi’s files as if you were

using a local disk. You cannot run any Rasberry Pi

programs this way however.

It is interesting if you cross-compile Pi programs on your PC,

which will be immediately visible on the Pi.

ssh the secure shell

In the case of ssh you have a single terminal window

that is connected to a shell on the Pi.

The command is:

ssh userOnPi@piIPaddress

Where piIPaddress can be the Pi’s IP address of hostname.

If you specify the -X option you can run X-11 based programs

where the X protocol is run over the ssh connection.

ssh session example

Here you see a screen dump from the PC with a remote terminal

that started an emacs session on the Pi.

Lecture 6

Uli Raich

UCC semester 2017/2018

Other RPI connections

• BPM180 barometric pressure sensor

Accessing the RPI remotely

Of course we can use the interfaces on the Raspberry Pi

to connect a screen, keyboard and mouse and use it in stand-alone mode

but we can also make use of the PC resources and access it remotely

There are several ways to access the RPI remotely:

• Using the VNC server on the Pi you can access it
  with a remote desktop from the PC
• The secure shell (ssh) allows you to get a remote terminal in the Pi
• With scp you can copy files back and forth between the Pi and the PC
• With nfs you can mount part of the Pi file system into the
  PC file system tree and access the PI SD card as if it was a local PC disk.

The remote Desktop

scp

To copy a file from the PC to the Pi this would be the command:

scp myfile.c uli@rpi-10:exercises/solutions/exercise_2

This will copy the file “myfile.c” into the sub-directory

exercises/solutions/exercise_2 on my home directory on the Pi.

Of course user uli must exist on raspberry10.

Instead of specifying the machine name: rpi-10

you can also give its IP address.

Compiling C programs for the Raspberry Pi

Just like Linux on the PC, Linux on the Raspberry Pi uses the GNU C compiler gcc.

The front end:

• Lexical Analyzer
• and the parser for the grammar

However, the code generator is different since now

we compile for the ARM processor and not the

Intel processor used on the PC

Cross-Compilation for the Pi

As explained in a previous lecture we can also compile

C programs for the Raspberry Pi on the

PC Linux system using a cross-compiler.

The cross compiler we will use is named

arm-linux-gnueabihf-gcc

and it is part of the tools package for the Pi.

It exists also as an Ubuntu package to be installed with apt.

• Raspbian, a Debian variant of Linux tailored to the Raspberry Pi.
• It contains most of the software packages you also find on Ubuntu
  The Desktop is however stripped down to make it more
  responsive on a processor that cannot cope with the speed of a PC
  This is what we are using!
• Ubuntu Mate is a Ubuntu variant for the Pi
• Windows 10 IOT core, a windows variant. I have never tried this but
  Windows gurus may give it a try if they cannot live without Windows on the Pi
• Android: There are several Android versions for the Pi floating
  around on the WEB. Your success on these may vary
• Kodi is a multimedia server that will allow you to listen to music,
  look at photos or watch films. Connect your Pi to a TV set
  (through the HDMI connector) and a stereo and off you go!

at the data sheet explaining them (205 pages!)

• General Purpose Input Output signals
• These are 3.3 V single pin signals used e.g. to drive a LED,
  a relay or any other device needing a digital signal level
• You can program it input or output
  • With pull-ups or pull-downs
  • To read switch state

• ADC
• DAC
• Real time clock
• EEPROM
• We also have a 2-line LCD display needing some 8 signals
  (+ power and gnd). A serial to parallel interface (shift register)
  with I2C interface eases the connection to the Raspberry Pi
  as only 4 serial signal lines are needed: SDA, SCL, Vcc, Gnd

More interfaces

There are more interfaces which we will not necessarily use during the course.

Students who think that they do not learn enough during this course

are invited to come forward.

We can easily give you more exercises, e.g to make

• The camera
• The touch screen interface
• The audio system
• Or the video system work

What you need to bring a RPI to life

This is what you will need to bring a Raspberry Pi to life:

• The Raspberry Pi board
• A case (this increases the chances the Pi will survive for more than a week)
• A 5V, 2.5A power supply with micro USB connector
• A USB keyboard and USB mouse
• A screen with HDMI connection of HDMI to VGA adapter

keyboard and mouse with your laptop or other computer

and access the Pi through a remote desktop.

The software

Go to the Raspberry Pi download page and download the

Raspbian image. It comes in 2 versions

• NOOBS which contains the system itself + an installer
• Raspbian proper. This version may be slightly more difficult to install
  because it does not have the installer, which you would keep on your
  SD card even though after its first use you don’t need it any more

$HOME/Downloads directory.

Since at Internet speeds that we experience at UCC this takes more than

1 hour to download we will distribute the zip file to all the PCs

How to extract the file system on Ubuntu?

Once downloaded we must first unzip the file:

Create a folder /opt/ucc/micros/raspberry and copy the zip file into it

cd /opt/ucc/micros/raspberry

cp ~/Downloads/2017-09-07-raspbian-stretch.zip .

unzip 2017-09-07-raspbian-stretch.zip which will give you

2017-09-07-raspbian-stretch.img

This is the file system image which will be copied to the SD card

bit by bit using the dd command

Structure of the image file

Can we know what is inside this image?

We see that there are 2 disk partitions:

• a FAT32 (Windows type) partition. This is the boot partition
• a Linux (ext4) partition which is the root file system

Looking inside the partitions

This is something only root (the superuser) can do

We loop mount the file system:

Now we can copy the contents to whatever directory we want

This is the boot partition

Then we can do the same thing for the root partition

The root partition

Once we mount the second partition the same way we see that it contains:

something we have seen before on our Ubuntu PC

The boot partition we have seen before is mounted on

/boot in this partition

How to get the OS onto the Raspberry Pi?

Now we have the OS on the PC where it does not help us much!

We must put it onto a media that can be read by the Rpi.

Traditionally this was the micro SD card

but you can also use certain types of USB memory sticks

(Be careful, not all sticks will work! I use a SanDisk cruzer)

Copying the OS to the SD card

If your PC has an SD card reader then you put the

micro SD card into a normal SD card holder.

Otherwise there are microSD to USB converters

First check which disks you have on you system:

Then you plug in your microSD adapter or your USB adapter

and do the same thing again

You should see 2 additional partitions, in my case probably

/dev/sdc /dev/sdc1 /dev/sdc2

Copy the OS

Now we are ready to copy the operating system to the SD card (or USB stick)

Where X is the disk letter (in our case “c”)

This may well take several minutes (the image is some 1.6 Gbytes!)

To see the progress:

The moment of truth

Safely remove the SD card from your system (unmount if mounted!)

Put it into the SD card slot of the Pi

Power on th machine

With a little bit of luck, it should boot

For more details of installing Raspbian on the SD card using a Linux system see

https://www.raspberrypi.org/documentation/installation/installing-images/linux.md

First login

Raspbian has a default user named

• pi
• with password raspberry (which must be changed
  immediately for security reasons!)

adduser uli and follow the instructions on the screen

usermod -a -G sudo uli

Then login with this new login name and

upgrade the system to the latest revision of all programs:

sudo apt update

sudo apt upgrade or sudo apt dist-upgrade

Adding software packages

Once you have come this far you may want to add

additional software packages, emacs being one of them

You will continue adding packages as you use the system

and you will see what is missing.

Configuring the system

We have seen that the system image takes 1.6 Gbytes our SD card

however provides 32 Gbytes. How to use it to its full capacity?

Start raspi-config (which is a program dedicated to the Raspberry

and does not exists und PC Ubuntu)

Go through all the options of the program and see if they make sense to you.

Lecture 5

Uli Raich

UCC semester 2017/2018

A first glimpse

There are several versions of Raspberry Pis available on the market:

• Raspberry Pi 1 Model B released in 2012
• There is also a simpler and cheaper model A
• Raspberry 2 with more memory
• Raspberry Pi zero a stripped down version for 5 US$
• Raspberry Pi zero W same as zero but with WiFi and Bluetooth for 10 US$
• Raspberry Pi 3 fully equipped model that we will be using

Raspberry Pi specs

Operating systems on the Pi

From the specs we can see that the Raspberry Pi 3 is a full blown computer.

With its

• 64 bit quad core processor
• 1 Gbyte of RAM
• 32 Gbyte of SD card

a full particle accelerator and it is also much more powerful

than the computer system that allowed the moon landing!

This allows a great deal of flexibility when it comes to

operating systems to be installed on the machine

Currently available OS

• Raspbian, a Debian variant of Linux tailored to the Raspberry Pi.
  
  
• It contains most of the software packages you also find on Ubuntu
  
  The Desktop is however stripped down to make it more
  
  responsive on a processor that cannot cope with the speed of a PC
  
  This is what we are using!
  
  
• Ubuntu Mate is a Ubuntu variant for the Pi
  
  
• Windows 10 IOT core, a windows variant. I have never tried this but
  
  Windows gurus may give it a try if they cannot live without Windows on the Pi
  
  
• Android: There are several Android versions for the Pi floating
  
  around on the WEB. Your success on these may vary
  
  
• Kodi is a multimedia server that will allow you to listen to music,
  
  look at photos or watch films. Connect your Pi to a TV set
  
  (through the HDMI connector) and a stereo and off you go!

BCM2835 CPU

The CPU has got an ARM processor core with 4 64 bit CPUs

The operating system and the Linux kernel are still 32 bit versions

(After the course you may try to compile and install

a 64 bit kernel yourself. This is a very good exercise to

understand how the OS is built!)

Around the CPU there are plenty of interfaces

To know the details (the interfaces only!) have a look at the data sheet explaining them (205 pages!)

BCM2835 peripherals

Here are some of the Raspberry Pi peripherals:

• UART
• SPI
• BSC (serial controller)
• DMA controller
• External mass media controller
• PCM / I2S Audio
• Pulse Width Modulation
• Timer
• USB
• I2C
• GPIO

Raspberry Pi and the real world

You can easily connect

• General Purpose Input Output signals
  
  
• These are 3.3 V single pin signals used e.g. to drive a LED,
  
  a relay or any other device needing a digital signal level
  
  
• You can program it input or output
  
  
  • With pull-ups or pull-downs
    
    
  • To read switch state
    
    
  • To drive a 3.3V output level (and light a LED)

Connection to bread board: The cobbler

Other Rpi connections

I2C is a serial bus often used in computer systems of for

short distance interfacing. Many devices having a I2C port

are available and we will program a few:

• ADC
  
  
• DAC
  
  
• Real time clock
  
  
• EEPROM
  
  
• We also have a 2-line LCD display needing some 8 signals
  
  (+ power and gnd). A serial to parallel interface (shift register)
  
  with I2C interface eases the connection to the Raspberry Pi
  
  as only 4 serial signal lines are needed: SDA, SCL,Vcc, gnd

Slide 1: The Raspberry Pi and how to bring it to life

-- Uli Raich - 2017-09-13

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