@Misc{Gandrass2022UniformTimerAPI,
  author   = {Niels Gandra{\ss}},
  month    = feb,
  title    = {{A Uniform API for Cross-Platform Timer Hardware Abstraction on Resource Constrained IoT Devices}},
  year     = {2022},
  abstract = {Timers are part of every microcontroller and influence numerous aspects of embedded applications. As the heterogeneous spectrum of timer peripherals continues to grow, embedded OSs increasingly struggle to expose novel timers and advanced features via their time-honoured APIs. The need for comprehensive and future-proof hardware abstraction therefore arises.
  
This work provides detailed insight into modern timer peripherals. We conduct a survey of timer hardware across 43 device families from eight manufacturers, characterize typical timeouts within IoT applications, examine timer APIs of popular embedded OSs, identify deficiencies of current solutions, and discuss different approaches to hardware abstraction. This forms a solid base, on which a two-layered low-level timer API design is proposed and implemented for the RIOT OS. Its uniform interface allows transparently interchangeable use of all hardware timers. Generic and peripheral-specific features are exposed, yet application portability is preserved. On average, available timers and channels are tripled, and previously unexposed advanced timer types such as ultra-low power timers become usable. Current interfaces are streamlined to form a single API, fostering uniformity and maintainability of timer code throughout the whole RIOT ecosystem.
  
We develop platform-independent timer unit tests and benchmark suites that are executed using a HiL testbed with CI support. The performance of our novel uTimer API is assessed on 14 MCUs. It only adds between six and 21 CPU cycles of abstraction overhead compared to existing solutions. This corresponds to timeout errors of less than 0.05 % while numerous modern timer features are made available to user applications and high-level OS modules. For high-performance use, deliberate renunciation of timer-type transparency eliminates any performance differences between APIs at the cost of narrowing application portability. Automated execution of the contributed unit tests and benchmarks on nightly builds and pull requests moreover facilitates the development of sustainable implementations and permits their sound evaluation.},
  keywords = {embedded systems, hardware abstraction, hardware timers, operating systems, resource constrained devices, software design},
}

@InProceedings{Gandrass2021uTimer,
  author    = {Niels Gandra{\ss} and Michel Rottleuthner and Thomas C. Schmidt},
  booktitle = {2021 IEEE International Conferences on Internet of Things (iThings) and IEEE Green Computing Communications (GreenCom) and IEEE Cyber, Physical Social Computing (CPSCom) and IEEE Smart Data (SmartData) and IEEE Congress on Cybermatics (Cybermatics)},
  title     = {{uTimer: A Uniform Low-level Timer API for RIOT OS}},
  year      = {2021},
  month     = dec,
  pages     = {1--8},
  publisher = {Institute of Electrical and Electronics Engineers (IEEE)},
  abstract  = {Microcontrollers offer a large range of hardware timers. As peripherals grow in diversity, the complexity of supporting them increases for embedded operating systems. Well-established software interfaces struggle with covering the full feature set of novel timers. This raises the need for a flexible hardware abstraction of timer peripherals.

In this paper, we first contribute an analysis of timer hardware that covers 43 device families from eight manufacturers and a survey of existing driver modules. We then derive uTimer, a uniform low-level timer API for the RIOT operating system. Its interface is independent of the timer type and allows for transparent use of all available peripherals. This fosters application portability across MCUs. We develop an automated benchmark suite that quantifies the abstraction overhead and compare the API performance to current solutions. Results show that uTimer introduces only six additional CPU cycles and preserves the timer performance.},
  doi       = {10.1109/iThings-GreenCom-CPSCom-SmartData-Cybermatics53846.2021.00016},
  isbn      = {978-1-6654-1762-4},
  keywords  = {embedded systems, hardware abstraction, hardware timers, operating systems, resource constrained devices},
  url       = {https://doi.org/10.1109/iThings-GreenCom-CPSCom-SmartData-Cybermatics53846.2021.00016},
}

@InProceedings{Gandrass2021TimerHardwareAnalysis,
  author    = {Niels Gandra{\ss} and Michel Rottleuthner and Thomas C. Schmidt},
  booktitle = {Proceedings of the 2021 International Conference on Embedded Software},
  title     = {{Large-scale Timer Hardware Analysis for a Flexible Low-level Timer-API Design: Work-in-Progress}},
  year      = {2021},
  address   = {New York, NY, USA},
  month     = sep,
  pages     = {35--36},
  publisher = {Association for Computing Machinery},
  series    = {EMSOFT '21},
  abstract  = {We report on our ongoing development of an optimized low-level timer-API for the RIOT operating system. Starting with a survey of hardware timer peripherals from 43 MCU-families and 8 manufacturers, we identify common properties and differences of all available timer types. Based on this hardware analysis, we propose a lightweight yet powerful low-level timer-API design. It streamlines existing timer interfaces and relieves application developers from the error-prone task of repeatedly writing additional peripheral driver code.},
  day       = {30},
  doi       = {10.1145/3477244.3477617},
  isbn      = {9781450387125},
  keywords  = {embedded systems, hardware abstraction, operating systems},
  location  = {Virtual Event},
  pagetotal = {2},
  url       = {https://doi.org/10.1145/3477244.3477617},
}

@InProceedings{Gandrass2021Examuntu,
  author    = {Niels Gandra{\ss} and Karin Landenfeld and Jonas Priebe},
  booktitle = {{SEFI2021 49th Annual Conference Proceedings - Blended Learning in Engineering Education: challenging, enlightening – and lasting?}},
  title     = {{Examuntu: A Secure and Portable Linux-Distributionfor Summative E-Assessments at Universities}},
  year      = {2021},
  address   = {Technische Universität Berlin, Germany},
  editor    = {Hans-Ulrich Hei{\ss} and Hannu-Matti J{\"a}rvinen and Annette Mayer and Alexandra Schulz},
  month     = nov,
  pages     = {836--843},
  publisher = {European Society for Engineering Education},
  abstract  = {As electronic assessments emerged into the academic landscape, specialized software solutions were developed along with them. Nowadays, many e-assessment systems that provide secure environments for digital examinations are available. However, they often lack portability or possess a complex software architecture that is laborious to maintain. In order to address these issues, we developed the Examuntu operating system. It provides a robust and secure e-assessment environment, being both lightweight and easily deployable in a wide range of computer pools, while allowing a flexible adaptation to multiple types of e-assessments and their respective software application requirements.
               With this paper, our contribution is twofold. First, we present the design of our novel e-assessment environment for computer pools. This includes the basic system architecture as well as individual aspects, such as web traffic filtering, browser security, and configuration management. Second, we report on our use of Examuntu in conjunction with a Moodle LMS during math lectures. Our setup features various question types and an optimized computer algebra system, allowing to parameterize exercises and generate differentiated feedback. We confirm that applied security measures did not negatively impact students by comparing their performance within digital to pen-and-paper examinations. Qualitative evaluations of three different e-assessment types show how students, assessment developers, and exam supervisors benefit from proposed Examuntu environment.},
  isbn      = {978-2-87352-023-6},
  keywords  = {e-assessment, e-assessment security, Moodle LMS, question parameterization, web filtering},
  url       = {https://www.sefi.be/proceedings/},
}

@InProceedings{Landenfeld2021DAP,
  author    = {Karin Landenfeld and Jonas Priebe and Niels Gandra{\ss}},
  booktitle = {Tagungsband Virtueller ASIM Workshop 2021 Simulation Technischer Systeme / Grundlagen und Methoden in Modellbildung und Simulation / Edukation und Simulation},
  title     = {{Digitale Aufgaben und Prüfungen in Mathematik – ein Erfahrungsbericht}},
  year      = {2021},
  month     = mar,
  pages     = {185--186},
  publisher = {ARGESIM Publisher, Vienna},
  series    = {{ARGESIM} Report},
  volume    = {45},
  abstract  = {Kaum ein Studiengang lässt sich heutzutage noch vollständig ohne digitale Komponenten denken. Insbesondere die Ausrichtung der Studieninhalte auf eine zunehmend digitale Arbeitswelt ist primärer Bestandteil aktueller Strategien zur Curriculumsentwicklung an Hochschulen. Dieses bedingt, dass sowohl die Lehre und das Lernen als auch das Prüfen digital ausgerichtet werden müssen. Nur so können die neu zu erwerbenden Kompetenzen auch in geeigneter Form gelehrt und geprüft werden.
               In diesem Beitrag stellen wir unsere Erfahrungen mit vorlesungsbegleitenden digitalen Übungsaufgaben zum individuellen Selbststudium vor und erläutern zwei verschiedene Szenarien zur Durchführung digitaler Prüfungen mit unterschiedlichen Randbedingungen.},
  doi       = {10.11128/arep.45},
  isbn      = {978-3-901608-69-8},
  keywords  = {automated grading, blended learning, education, electronic assessments, online assessments},
  url       = {https://www.cea-wismar.de/asim2021/tagungsband/},
}

@InProceedings{Gandrass2020OPPSEE,
  author    = {Niels Gandra{\ss} and Torge Hinrichs and Axel Schmolitzky},
  booktitle = {Tagungsband des 17. Workshops "Software Engineering im Unterricht der Hochschulen" 2020, Innsbruck, {\"{O}}sterreich, 26. - 27.02.2020},
  title     = {{Towards an Online Programming Platform Complementing Software Engineering Education}},
  year      = {2020},
  editor    = {Stephan Krusche and Stefan Wagner},
  month     = feb,
  pages     = {27--35},
  publisher = {CEUR-WS.org},
  series    = {{CEUR} Workshop Proceedings},
  volume    = {2531},
  abstract  = {Existing online programming platforms provide many opportunities for individuals to develop and improve their programming skills. Using descriptive assignments that address different skill levels these platforms target both beginners and experienced programmers. We used one such platform featuring advanced exercises in a project course during the fifth semester of our bachelor degrees in computer science and were surprised by its success and the high motivation of the participants. Nonetheless, we also observed deficits of the platform with regard to software engineering aspects. In this paper we identify requirements for an online programming platform that complements software engineering education and match existing platforms against these proposed requirements.},
  keywords  = {education, online assessment, online programming platform, programming, software engineering education, team programming},
  url       = {http://ceur-ws.org/Vol-2531/},
}

@InProceedings{Gandrass2019ABPJava,
  author    = {Niels Gandra{\ss} and Axel Schmolitzky},
  booktitle = {Proceedings of the Fourth Workshop "Automatische Bewertung von Programmieraufgaben" (ABP 2019), Essen, Germany, October 8-9, 2019.},
  title     = {{Automatisierte Bewertung von Java-Programmieraufgaben im Rahmen einer Moodle E-Learning Plattform}},
  year      = {2019},
  month     = oct,
  pages     = {3--10},
  publisher = {Gesellschaft für Informatik e.V.},
  abstract  = {Die Programmiersprache Java wird an zahlreichen Hochschulen gelehrt, um Studierende mit grundlegenden Programmierkonzepten vertraut zu machen. Zur Integration von Online-Java-Programmieraufgaben in ein Moodle LMS wurde ein Fragetyp entwickelt, welcher die parallele Ausführung sowie die automatisierte Bewertung von Quellcode auf Basis von JUnit-Tests ermöglicht. Studierende erhalten hierbei ein sofortiges und individuelles Feedback, welches dynamisch schon während der Bearbeitung einer Aufgabe erzeugt wird. In diesem Beitrag werden sowohl die technischen Details des entwickelten Fragetyps als auch erste Erfahrungen mit seinem Einsatz in der Programmierlehre an der Hochschule für Angewandte Wissenschaften Hamburg thematisiert.},
  crossref  = {DBLP:conf/abp/2019},
  doi       = {10.18420/abp2019-1},
  keywords  = {automated code evaluation, feedback generation, grading, Java, Java class isolation, JUnit, learning management system, Moodle, signature validation, web service},
  url       = {https://doi.org/10.18420/abp2019-1},
}

@Misc{Gandrass2019CeilometerML,
  author   = {Niels Gandra{\ss}},
  month    = apr,
  title    = {{Unsupervised Machine Learning: Feature Extraction for Classification of LIDAR-Ceilometer Aerosol-Backscatter Profiles}},
  url      = {http://edoc.sub.uni-hamburg.de/haw/volltexte/2019/4870/},
  year     = {2019},
  abstract = {In this bachelor thesis a method for unsupervised feature extraction from aerosol backscatter profiles is proposed. After a first data preprocessing step the LIDAR-ceilometer datasets are converted into an compressed representation using an convolutional autoencoder. These encoded representations are then used for the computation of an initial cluster assignment which gets further optimized, trough minimizing the KL-divergence to an arbitrary target distribution, during consecutive training. Two experiments, the first based on the MNIST database of handwritten digits and the second based on real ceilometer aerosol backscatter data, were successfully executed. The proposed method has been successfully utilized, in order to group some meteorological phenomena into clusters which then labels were assigned to. In addition to the description of implementation details, multiple aspects of the ceilometer datasets are analyzed and a comprehensive outlook to further possible research in this field is given.},
  keywords = {autoencoder, backscatter analysis, clustering, cluster optimization, CNN, dimensionality reduction, feature extraction, LIDAR-ceilometer, machine learning, multi-stage learning, signal filtering, sliding-window, soft-clustering, unsupervised learning},
}

@Book{Palm2017NSH,
  author    = {Philipp Palm and Nena Kerner and Sarah Alexi and Lilly Bekesch and Janina Bergerhoff and Simon Berthold and Corvin Busch and Jonathan Erl and Niels Gandra{\ss} and Peter Gray and Birgit Heidenreich and Charlotte Heidenreich and Shari Hesse and Sylvia Hesse and Gerald H{\"u}ther and Carola Keller and Anja Kern and Samuel Kerner and Markus Kr{\"o}ger and Greta Lummitsch and Luka Mahlau and Nick Meier and Vio Petram and Anne Romero-Fr{\"u}h and Mimsy Sadofsky and Christopher Wagner},
  publisher = {NullPunkt \& Komma Verlag},
  title     = {{Werden? Ich bin doch schon!: Neue Schule Hamburg}},
  year      = {2017},
  isbn      = {978-3962780005},
  month     = nov,
  abstract  = {Die Neue Schule Hamburg ist eine demokratische Schule, die konsequent die individuelle Freiheit ihrer Schülerinnen und Schüler in den Mittelpunkt stellt. Doch wie wird das gemeinschaftliche Zusammenleben an solch einer Schule gestaltet? Zum zehnjährigen Jubiläum erzählt die Neue Schule Hamburg sich selbst: Schüler, Mitarbeiter, Eltern, Gründer geben Einblicke in ihre Praxis und die damit verbundene Philosophie.},
  keywords  = {education, pedagogics, alternative educational systems, sudbury school, social sciences, learning, motivation, democratic education},
}