You (Might) Only Need a Microcontroller (and a Server) for Computer Science

Introduction

I recently read a blog post that got me nerdsnipped. The blog post was: You Only Need a Tablet for Computer Science. In here, Ezri talks about the setup they use. An iPad and a server. Using the tablet just to connect to a server. That got me thinking. What is the least amount of power you need to connect to an actual server? Enter the ESP8266.

The ESP8266 is a microcontroller that can connect to the internet and has the following specs:

• Processor: L106 32-bit RISC microprocessor core based on the Tensilica Diamond Standard 106Micro running at 80 or 160 MHz.
• Memory: 160KiB of RAM total.
• 32 KiB instruction RAM
• 32 KiB instruction cache RAM
• 80 KiB user-data RAM
• 16 KiB ETS system-data RAM
• External QSPI flash: up to 16 MiB is supported (512 KiB to 4 MiB typically included)

As per wikipedia.

I bought a couple of this badboys last year for my final project of the microcontrollers class. I had them lying around and thought that it would be fun to use them to connect to my computer.

Connecting to my computer

I decided that I wanted to do a simple proof of concept to demonstrate that it is possible to connect from a micro to my computer. The ESP8266 is powerfull enough to run something like an SSH client, right?

After a swift fifteen minutes of searching, all I could find was a library that implemented SSH servers and clients for the ESP32. But I did not want to port an entire library just for a nerdsnipe.

I decided that I should use something a bit older, telnet!

Disclaimer: telnet makes all your communications in plain text so you should not use it for anything serious. But I am not making something serious.

There is a port of an Arduino™ library for ESP32 to ESP8266 that almost works.

I imported the library to the arduino™ IDE and when I tried compiling the example. I got some compilation errors.

A quick fix of two lines got this running.

-#include "ESP8266telnetClient.h"
+#include "ESP8266TelnetClient.h

and

bool ESP8266telnetClient::sendCommand(const char* cmd){
    
    this->send(cmd);
    //negotiation until the server show the command prompt again
    if (strcmp(cmd, "exit") != 0){
        return this->waitPrompt();
    }
    else{
        this->disconnect();
+       return false; // not even sure if this is should work lol
    }
    
}

I made a telnet server on my computer and I ran the example code, it ran. I had successfully run a telnet client from this Microprocessor.

But the example code only had hard coded commands and I wanted a more interactive shell. So I decided to code something simple up and modify the example. I made a kind of interactive shell with the help of chatgpt:

void setup() {
  // Wifi setup...
  tc.setPromptChar('$');

  char key = 0;
  Serial.println("\r\nPress Enter to begin:");
  do {
    key = Serial.read();
  } while (key <= 0);

  if (tc.login(laptop, user, pwd)) {
    tc.sendCommand("ls -l");
    tc.sendCommand("ifconfig");
    interactiveShellActive = true; // Set interactive shell flag to true
    interactiveShell(); // Call the interactive shell function
    interactiveShellActive = false; // Reset the interactive shell flag
  }
  else {
    Serial.println("Login failed");
  }
}

void loop() {

}


void interactiveShell() {
  Serial.println("Interactive Shell. Type 'exit' to end.");
  while (true) {
    //Serial.print("Enter command: ");
    String command = readSerialStringUntil('\n');

    if (command == "exit") {
      break; 
    }

    tc.sendCommand(command.c_str());
  }
}


String readSerialStringUntil(char delimiter) {
  String inputString = "";
  while (Serial.available() > 0) {
    char c = Serial.read();
    if (c == delimiter || c == '\n') {
      break;
    }
    inputString += c;
  }
  return inputString;
}

Finally, I ran this and had an interactive shell through telnet! There is a problem with this code though, the shell keeps printing again and again and again. But, it’s a full terminal!

You can only communicate with this terminal one line at a time. So no VIM in this shell :(. Buuuut, you still have ed!

So you can write stuff like:

$ ed
a
Hello, World!
.
wq

Conclusion

You can absolutely do better than this. It was a fun tangent for a day. For now, I rest my case. You only need a microcontroller with a total of 160KiB of RAM to go to university.

If you want to read the code, it is in my repo with the “patched” library m.

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