This directory contains all the information necessary to set up and interface with the RIS prototype.
RIS configurations are sent over a WiFi link hosted on the Raspberry Pi 3B. A socket is established with MATLAB acting as the client, connecting to a server running on the Raspberry Pi. The server-side software is currently written in Python. Configurations sent via MATLAB are transformed into the correct format by the Python program on the Pi side. The Pi then sets the digital states of the GPIO pins to program the shift registers on the respective RIS tiles.
It is possible to connect to the Raspberry Pi via an ethernet cable through a secure shell through the command:
with the default password.
By default, the access point on the USC prototype is set up on boot, with an access point name PiRS. The password is the default and won't be posted here for obvious reasons (just ask James or others in the project).
To set up an access point on the Raspberry Pi 3B from a fresh install, see the guide posted here. Note the static IP address you use in the interfaces file.
As an alternative, you may set up a mobile hotspot on a PC and get the Pi to connect to you. To keep things simple, you may connect a monitor/keyboard/mouse to the Pi the first time you do this.
The current procedure for setting up a socket for RIS control involves:
- Connect to the PiRS WiFi access point from the user machine
- Establish control of the Pi via SSH (i.e., via the command ssh pi@192.168.4.1). Use the default username and password.
- Run the program python ~/control/socket-server-tiles.py
- Note the port number port_number (this can be found in the PORT variable in the program)
- In MATLAB on the user machine, run the command sock = tcpclient("192.168.4.1", port_number) where port_number is an integer of the port number displayed when running the server
Configurations are sent over the socket in the form of a string of bits. Additionally, a tile number is sent so that the Pi knows which set of GPIO pins it should send the control signals over.
Each RIS tile requires 6 digital inputs alongside a DC voltage and a ground connection. The DC voltage should be the same level as the logic high. For the Raspberry Pi 3B, this will be 3.3 V.
| Pin # | ID | Function | T1->Raspberry Pi | T2->Raspberry Pi |
|---|---|---|---|---|
| 1 | NC | Not connected | - | - |
| 2 | NC | Not connected | - | - |
| 3 | D4 | Data line 4 | 3->12 | 3->19 |
| 4 | D3 | Data line 3 | 4->10 | 4->18 |
| 5 | L | Latch (shifts out data to shift register outputs) | 5->5 | 5->13 |
| 6 | D2 | Data line 2 | 6->8 | 6->16 |
| 7 | C | Clock (timing signal) | 7->3 | 7->11 |
| 8 | D1 | Data line 1 | 8->7 | 8->15 |
| 9 | GND | DC ground | 9->6 | 9->14 |
| 10 | GND | DC ground | - | - |
| 11 | Vcc | DC voltage (3.3 V for Pi 3B) | 11->1 | 11->17 |
| 12 | Vcc | DC voltage (3.3 V for Pi 3B) | - | - |
The pinout of the Raspberry Pi 3 will depend on the number of tiles that are utilised for a particular arrangement. This is governed by the tile.h file in this directory. The pin mapping for two tiles is shown in the two right-hand columns in the table above. The Pi GPIO pin numbers refer to the board numbering scheme (i.e., the physical pin number). For more information on the Raspberry Pi GPIO interface, see here.
If for whatever reason you need to access the graphical user interface (GUI) of the Raspberry Pi, you can use a VNC viewer. One such program is RealVNC which can be found here. Follow the first two instructions in the Socket Setup section above, then:
- In the secure shell, run the command vncserver. Note down the IP address and the number following the colon.
- Open VNC Viewer or an equivalent program. Use the VNC server address 192.168.4.1:# where # is the number obtained in the previous step (typically defaults to 1 if no other session is open).
- Enter the username and password of the Pi. This is set to default.