Practice 20 December 10, Wireless Access. Graduate course in Communications Engineering. University of Rome La Sapienza. Rome, Italy

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1 Practice 20 December 10, 2018 Wireless Access Graduate course in Communications Engineering University of Rome La Sapienza Rome, Italy

2 Wireless Access Networks for Raspberry Pi

3 Wireless Access Networks for Raspberry Pi Raspberry Pi Characteristics Support within MATLAB and Simulink HopeRF RFM73P-S2 Characteristics Connection to the Raspberry Pi The WAN4RP MATLAB library Low-level functions The image transfer application Introduction to Simulink The WAN4RP Simulink model Project website:

4 Connection to the Raspberry Pi The MATLAB Hardware Support Package for Raspberry Pi will be used to connect MATLAB with the Raspberry Pi during the WAN4RP project The package provides access to the Raspberry Pi through the Ethernet interface The package is available for download within MATLAB, in the Add-Ons section

menu Next, select Get Hardware Support Packages In the

5 Installation of Hardware Support Packages From the Home tab of the MATLAB main window, select the Add Ons menu Next, select Get Hardware Support Packages In the window coming up next, select Raspberry Pi among vendors:

Installation of Hardware Support Packages After the Hardware Support Package is installed, MATLAB will propose you to configure a Raspberry Pi board by formatting its micro-sd card: There should be

6 Installation of Hardware Support Packages After the Hardware Support Package is installed, MATLAB will propose you to configure a Raspberry Pi board by formatting its micro-sd card: There should be no need to go through this step, as the boards we are providing are already pre-configured to work with MATLAB R2017a (or R2017b) If you need to configure a Raspberry Pi later on, type targetupdater at the MATLAB command prompt and you will be guided through the procedure

Raspberry Pi Model B+ Released in July 2014 40 General Purpose Input Output (GPIO) pins Micro SD slot 4 USB ports & HDMI output Ethernet

7 Raspberry Pi Model B+ Released in July General Purpose Input Output (GPIO) pins Micro SD slot 4 USB ports & HDMI output Ethernet Raspbian OS (Linux Debian port), Micro USB power connector Important: a Raspberry Pi is a computer with a modern OS -> it requires a proper shutdown!

8 Raspberry Pi Model B+ Supported in MATLAB by means of set of dedicated functions We will review here a few relevant ones, but refer to MATLAB help/tutorials for more details Underlying communications between MATLAB and the RaspberryPi take place using SSH over Ethernet IMPORTANT: Your computer will need a proper Ethernet network configuration in order to reach the Raspberry Pi board (both during and after configuration)- Example for MATLAB2018b IP address: Netmask: Gateway:

9 Raspberry Pi Model B+ mypi=raspi(ip, login, password, port) Returns a handle to a MATLAB object used to communicate with the Raspberry Pi board mypi=raspi works as well, and uses default values. In MATLAB 2018b: IP= login = pi password = raspberry The handle can be use to send commands to the RPi and interrogate it

10 Raspberry Pi Model B+ value=readdigitalpin(mypi,pinnumber) Returns the value of the pinnumber GPIO pin on the Raspberry Pi value=writedigitalpin(mypi,pinnumber) Sets the value of the pinnumber GPIO pin on the Raspberry Pi configuredigitalpin(mypi,pinnumber,'output') configures the pinnumber GPIO pin on the Raspberry Pi as output (or input, if used with input )

11 Raspberry Pi Model B+ enablespi(mypi) Enables the Serial Peripheral Interface (SPI) on the Raspberry Pi The SPI interface uses 4 out of the 40 GPIO pins on the RPi, and is used to control SPIenabled devices such as the RFM73P-S2 mypi.availablespichannels Lists the available SPI channels (2 in the case of the Raspberry PI Model B+)

12 Raspberry Pi Model B+ RFM73=spidev(mypi, CE0 ) Returns a handle to a MATLAB object connected to a SPI device controlled by the RaspberryPi, along with the characteristics and capabilities of the SPI device outvector=writeread(spidevid,data); Exchanges data with the SPI device connected to the Raspberry Pi

13 Raspberry Pi Model B+ h = raspberrypi Returns a handle to a MATLAB object connected to the Raspberry Pi, but differently from the raspi function, this is treated as alinux object. It allows to send system commands to the Linux OS, for example for shutting down the board before unplugging it: h.execute('sudo shutdown -h now )

14 Additional communication tool BitVise SSH client SSH/SFTP client to connect and send data/commands from Windows to Raspberry Pi Available for download at: Install it for the shutdown of the RPi

15 HopeRF RFM73P-S2 The HopeRF RFM73P-S2 is a wireless transceiver operating in the ISM band at 2.4 GHz Main characteristics: GFSK modulation with 1 MHz channel width 250 kbits/s, 500 kbits/s, 1 Mbit/s and 2 Mbits/s available rates -10 dbm, -5 dbm, 0 dbm and 5 dbm available output power RSSI and carrier sensing CRC coding Automatic Packetization, Ack and Retransmission

16 HopeRF RFM73P-S2 Block diagram

17 HopeRF RFM73P-S2 Input/output SPI The 10 pins are connected to 10 GPIO pins on the Raspberry Pi Pin-out is available at

18 HopeRF RFM73P-S2 Packet format Address: it is the address of the intended receiver, but is also used by the receiver as the TX address for automatic packet acknowledgment A device can receive at the same time on up to 6 RX addresses, in order to support star configurations

19 HopeRF RFM73P-S2 Unless a packet is explicitly set to be transmitted without acknoledgment, the TX will wait for an acknowledgment by the RX In case of a missing acknoledgment, the TX will wait for a timeout (up to 4 ms) and retransmit the packet The TX will retransmit the packet up to 15 times and then give up with a IRQ to the master Both timeout and number of retransmissions can be configured

20 HopeRF RFM73P-S2 Configuration of the RFM73P-S2 takes place by properly setting two banks of registers accessible through the SPI interface The writeread MATLAB function seen before is thus the core method to communicate with the RFM73P-S2 User data is also written and read through the SPI interface, by using two dedicated registers configured as FIFO queues Additionally, active low or high signals must be set on the other PINs, using the writedigitalpin function

21 HopeRF RFM73P-S2 (Almost) complete information about the operation and configuration of the RFM73P- S2 is available in datasheet provided by HopeRF The datasheet is available for download at READ IT!

22 The WAN4RP MATLAB library Provides a set of MATLAB functions, built on the writeread function, supporting data exchange with and configuration of the RFM73P-S2 The library is available for download at A brief description is provided in the following, but refer to the documentation within each MATLAB file for details

23 The WAN4RP MATLAB library RPi_RFM73_initial_connection The script creates handles to the RPi board and to the RFM73P transceiver, and returns the handles [mypi, RFM73] [status]=rfm73_init(rpidevid, spidevid) The function configures a RFM73 device connected to a RPi board This is the place for user-defined configuration! [status]=rfm73_switch_to_rx(rpidevid, spidevid) The function puts a RFM73 device into RX mode, continously searching for packets

24 The WAN4RP MATLAB library [readdata,status]=rfm73_receivepacket(spidevid) The function reads content from the RX FIFO register, and returns a vector containing the data. [status]=rfm73_switch_to_tx(rpidevid, spidevid) The function puts a RFM73 device into TX mode, ready to send a packet as soon as data is loaded in the TX FIFO [status]=rfm73_sendpacket(rpidevid,spidevid,typ e,writedata) The function puts content into the TX FIFO and specifies if ACK is required for the corresponding packet (see file for details)

25 The Image Transfer example Two high level functions are provided on the project website as an example of how the low level functions can be used in a real world application [imgarraydata, successrate] = RFM73_transmitImage(rpidevID, spidevid, filename, format, maxbyteperpacket ) The function reads an image from file and breaks it in blocks of maxbyteperpacket, while generating control information required for reception. [rximagearray] = RFM73_receiveImage(rpidevID, spidevid, maxbyteperpacket ) The function receives an image broken in blocks of maxbyteperpacket bytes, and uses control information to rebuild an array containing the image data

26 Available for download at: The Image Transfer example demo.zip Also che check a simpler example of a Master-Slave connection: emo.zip

Raspberry Pi Setup Tutorial

Raspberry Pi Setup Tutorial The Raspberry Pi is basically a miniature linux- based computer. It has an ARM processor on it, specifically the ARM1176JZF- S 700 MHz processor. This is the main reason why