Embedded Computing 1 (STECE-2024): Summer

Semester Information

• Embedded Computing 1 (STECE-2024): Syllabus

• Git repository: https://codeberg.org/jfasch/FH-STECE2024

2026-02-22: Intro: OS And C++ (Live Demo)

Livehacked by teacher

• Login to Pi at home: ssh -p 2022 jfasch.bounceme.net

$ ls -l /sys/class/hwmon/
$ ls -l /sys/class/hwmon/hwmon2/

• Show how to use that sensor from the commandline (Linux and OneWire (using DS18B20 Temperature Sensor as Slave))

• Write a C program that reads the sensor value in a loop (a “data logger”, so to say). (System Calls)

• Transform the sensor into a dedicated type/class (Data Encapsulation)

code/intro.cpp

#include <iostream>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#include <time.h>
#include <sys/types.h>

#include <string>
#include <stdexcept>


class Thermometer
{
public:
    Thermometer(const std::string& filename)
    {
        _fd = open(filename.c_str(), O_RDONLY);
        if (_fd == -1)
            throw std::runtime_error("nix open");
    }

    ~Thermometer()
    {
        close(_fd);
    }

    double get_temperature() const
    {
        char buffer[64];
        ssize_t nbytes = read(_fd, buffer, sizeof(buffer)-1);
        if (nbytes == -1)
            throw std::runtime_error("nix read");

        off_t newpos = lseek(_fd, 0, SEEK_SET);
        if (newpos == -1) {
            throw std::runtime_error("nix lseek64");
        }

        buffer[nbytes] = '\0';
        int milli_celsius = std::stoi(buffer);
        double celsius = milli_celsius / 1000.0;
    
        return celsius;
    }

private:
    int _fd;
};


int main(int argc, char** argv)
{
    if (argc != 2) {
        std::cerr << "nix zwei argumente" << std::endl;
        return 1;
    }
    const char* filename = argv[1];
    Thermometer thermo(filename);

    while (true) {
        std::cout << thermo.get_temperature() << std::endl;

        timespec interval = { 1, 0 };
        int rv = nanosleep(&interval, nullptr);
        if (rv == -1) {
            std::cerr << "nix sleep?" << std::endl;
            return 1;
        }

    }
    
    return 0;
}

2026-02-2{3,4}: Prepare Work Environment

Install OS

Current options …

• Use Egon Teiniker’s Debian VirtualBox image from previous semesters

  • Pro: already there

  • Con: compiler version might be too low for our C++ topics

• Use Windows Subsystem for Linux (WSL2), see Windows Subsystem for Linux (WSL)

  • Pro

    • Seamless integration with Windows

    • VS Code extension(s) available

    • The way to go

  • Con

    • No Linux GUI program possible (yet)

• Use MacOS

  • Pro: already there

  • Con: not Linux, for that matter

• Use Linux

  • Pro: best

  • Con: none

Programming Environment, Project

• Clone and build project according to its build instructions

  https://codeberg.org/jfasch/FH-STECE2024

2026-03-02 (3VO): File I/O And Systems Programming, Homework

Permissions Intro

From Permissions: Mode, User and Group Ownership

• Owner and Permissions

• A Simple Example

• Permission Check: User

• Shell Commands: Tuning Permissions

Program Entry And Exit

• Process Termination: Exit Status

• Argument Vector (argv)

System Calls Intro

• System Calls: Overview

• errno, And Error Handling

File IO

From Files And File Descriptors

• File Descriptors: Basics

• open(): Opening Files

• Reading Files

• Writing Files

• Creating Files

Homework

Homework

• Homework: cp-for-the-poor (2026-03-02)

2026-03-09 (3UE*2): File I/O (Homework)

Continuing with homework from last time around …

• Trainer pushes missing artifacts (argh)

• Trainer live-hacks solution

Homework

• Due date: 2026-03-13

• Homework: cp-for-the-poor (2026-03-02)

2026-03-13 (3VO): Git (SSH), C++ Intro

Trainer’s note

• Ensure that we access the repo over HTTPS and see a password prompt

Basic git Workflow: add, commit, push (, pull)

• View changes

  Current working directory somewhere inside the tree,

  $ git status
  ...
  

• git add changes: stage for next commit

  $ git add file.h file.cpp
  ...
  

  Review repo situation

  $ git status
  ...
  

• git commit what you staged

  Either non-interactive (giving the commit message as a commandline parameter)

  $ git commit -m 'frobozz the foobar'
  

  Or letting git pop up your favorite $EDITOR

  $ git commit
  

• git push

• git pull

SSH, And Using It For Git Repository Access

See also

• SSH: Basics

• SSH: Public Key Authentication

• SSH: Secure Copy (scp)

• SSH: Port Forwarding

• SSH File System (sshfs)

From SSH: Secure Shell:

• SSH: Basics

• SSH: Public Key Authentication

Exercise: Key Pair, Deployed To Codeberg

• Create key pair. Leave passphrase empty (else you’ll have to type it in over and over, just like the HTTPS password)

• Send to trainer

  • Public key (id_rsa.pub)

  • Codeberg account name

• Deploy SSH public key on Codeberg (account (icon above right) -> “Settings” -> “SSH / GPG keys”)

• You have a clone of your fork of the upstream repo; change that clone’s upstream URL from HTTPS to SSH.

  First, look:

  $ git remote
  origin
  $ git remote -v
  origin     https://codeberg.org/_codebergaccountname_/FH-STECE2024.git (fetch)
  origin     https://codeberg.org/_codebergaccountname_/FH-STECE2024.git (push)
  

  Then set:

  $ git remote set-url origin ssh://git@codeberg.org/_codebergaccountname_/FH-STECE2024.git
  

Distributed git: Update Your Fork From Upstream

Current situation

Wanted: merge changes from upstream

• Create a remote for upstream https://codeberg.org/jfasch/FH-STECE2024.git

  $ git remote add upstream https://codeberg.org/jfasch/FH-STECE2024.git
  

  $ git remote -v
  origin     https://codeberg.org/_codebergaccountname_/FH-STECE2024.git (fetch)
  origin     https://codeberg.org/_codebergaccountname_/FH-STECE2024.git (push)
  upstream   https://codeberg.org/jfasch/FH-STECE2024.git (fetch)
  upstream   https://codeberg.org/jfasch/FH-STECE2024.git (push)
  

• Fetch from upstream

  $ git fetch upstream
  ... roedel ...
  

• Merge upstream/master into your local master branch

  Check that your current branch is master,

  $ git branch
  * master
  

  Merge,

  $ git merge upstream/master
  

  Note that this is not always so easy - you might have to resolve conflicts.

  Push to default location - your fork,

  $ git push
  

• Shorthand: git pull. This is the same as fetch followed by merge

2026-03-16 (3UE*2): Exercise: PWM Controller (TDD)

See Homework: PWM Controller (2026-03-16)

2026-03-20 (3VO): cp-for-the-poor (Recap), C++ Intro

Exercises

• Homework: cp-for-the-poor (2026-03-02)

  • Closed; was optional anyhow

  • List of pull requests

    • Morena_M (REJECTED): rejected: build/ added

    • johanneshranitzky (DONE): conflict marker committed

    • pholz (DONE): (sehr geil)

    • FarzanehN (REJECTED): unrelated changes (my-codeberg-name)

    • KoenigMaxi (REJECTED): exit status 130

  • ⟶ Complaint summary: build/ directory part of PR, unrelated changes, …

  • Sommer_r: strace session :-)

• PWM exercise ongoing, questions

Commandline Repetition

From The Shell (Bash - “Bourne Again Shell”) in Linux Basics:

• Commandline

• Absolute and Relative Paths

• Special Paths

• Directory Listings: The ls Command

• Current Working Directory

• Creating And Removing Files and Directories

• Copying: cp

• Moving and Renaming: mv

• Symbolic Links, Hard Links

• Shell Configuration File: ~/.bashrc

Exercise

• Exercises: Create/Copy/Move/Remove

2026-03-23 (3UE*2): PWM Exercise, Shell Exercise

• Exercises: Create/Copy/Move/Remove

  Show an inline loop, reading temperature. Discuss the nature of true and false, and [. Transform into shell script. Initially without shebang, but 755, then explain interpreter line.

• Bring PWM exercise to an end

Near Future

C++ Intro

• Introduction

From Data Encapsulation:

• Object Oriented Programming In Good Ol’ C

• Classes and Objects

• Custom Constructor

• Default Constructor