Purpose
This project shows you how to use a USB- to-serial cable to interact directly with the Raspberry Pi from your laptop. This emulates the behavior of the RPi as if it were connected to a keyboard and simple character-based terminal. This is extremely powerful and will be the primary way you interact with the board from now on. Like the previous project, this project is less about code development and more about giving you tools that you will use from now on.
Get a Console Cable
The figure above shows what we’re talking about here, as well as how it is connected to the board. The “console cable” is a hybrid cable with a USB plug on one end, which goes into your laptop, and at the other end it has 4 female pin-header connectors. The UART output (a serial port) of the Raspberry Pi
© Copyright 2020 Bruce Jacob, All Rights Reserved
1
ENEE 447: Operating Systems — Project 1
uses pins 6, 8, and 10 of the GPIO header block (for ground, transmit, and receive, respectively), as well as pin 2 for power. You can buy the cable at the following site: https://www.adafruit.com/product/954
The site also provides a very good tutorial on how to set it up and use it:
https://learn.adafruit.com/adafruits-raspberry-pi-lesson-5-using-a-console-cable
Note that, even though you can use pin 2 to power the board via the USB, it is less than ideal for debugging, because whenever you try to toggle power by disconnecting the pin header, the serial connection gets disconnected, which can be a pain, and you might not be able to tell the difference between your code failing to boot, your code booting but not printing to the screen (i.e., failing to transmit characters over the wire), or all of it working fine.
Hook It Up
You may need to load a driver for the cable (see the tutorial), and once it is loaded, and the cable plugged into your laptop, you will see a special device appear, due to the cable having an ASIC in it that identifies to the laptop its special-device nature.
Follow the directions to establish a terminal connection with the USB/serial device on your laptop (e.g., on macOS, in the Terminal app, you type “screen /dev/cu.SLAB_USBtoUART 115200”). At that point, you can move to the next step and run the code in the Project 1 directory, which is a simple echo server. All it will do is wait for your first input and then begin echoing whatever you type but translated to upper - case (just so that you know your text is being received, processed, and then echoed by your software). You should see this:
<NAME>’s system is booting.
Please hit enter to continue.
At this point, the software is waiting for you to type something. Once you do, it will output some useful data-size information and then print the following:
Running ECHO server.
And, from this point on, everything you type on the keyboard will be reflected back to you, except that it will be in upper-case letters.
All you need to do is change <NAME> to your own name.
Customize It, Build It, Load It, Run It
Once you have it working, show us.
© Copyright 2020 Bruce Jacob, All Rights Reserved
2
