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CS140E: embedded operating systems (Engler, Winter, 2023)

This repository contains all material for CS140E, winter 2023.


CS140E is an introductory operating systems course. It roughly covers the same high-level material as CS 212 (formerly CS 140), but with a focus on embedded systems, interacting directly with hardware, and verification. Both courses cover concepts such as virtual memory, filesystems, networking, and scheduling, but take different approaches to doing so. By the end of 140E, you will have (hopefully) built your own simple, clean operating system for the widely-used, ARM-based Raspberry Pi.


  • Dawson Engler (engler);
  • Akshay Srivatsan (akshay01);
  • Alex Fu (afu625);
  • Manya Bansal (manya227).
  • Joe Tan.


140e is a lab-based class with no explicit lectures. We will do two five to eight hour labs each week. You should be able to complete almost all of the lab in one sitting. There will be several homeworks, that act as mini-capstone projects tying together the preceding labs.

By the end of the class you will have built your own simple, clean OS for the widely-used, ARM-based raspberry pi --- including interrupts, threads, virtual memory, and a simple file system. Your OS should serve as a good base for interesting, real, sensor-based / embedded projects.

We try to work directly with primary-sources (the Broadcom and ARM6 manuals, various datasheets) since learning to understand such prose is one of the super-powers of good systems hackers. It will also give you the tools to go off on your own after the course and fearlessly build sensor-based devices using only their datasheets.

This course differs from most OS courses in that it uses real hardware instead of a fake simulator, and almost all of the code will be written by you.

After this quarter, you'll know/enact many cool things your peers do not. You will also have a too-rare concrete understanding of how computation works on real hardware. This understanding will serve you in many other contexts. For what it is worth, everything you build will be stuff we found personally useful. There will be zero (intentional) busy-work.

Who should take this class.

The goal of the class is to help students who are very motivated and/or very good to go far, quickly. We focus on building small, simple but real OS subsystems --- threading, virtual memory, etc --- that can be used to build many other things.

You should take this class if:

  1. You write systems code well OR (you don't yet write code well AND have a lot of time to devote to the class);

  2. AND you find these systems topics interesting.

The people that found the class valuable in the past were entirely drawn from this demographic. I would say that if you struggle building stuff and are not already interested in the topic, then it's probably better to take a different class. I would particularly advise against taking this class if you were looking for an easier way to satisfy a cs140 requirement.

  1. It always helps, but you do not need any background in hardware or OS stuff to do well in the class. In fact, you don't even need to have been trained in CS: one of the best students from the past was a physics PhD student with fairly minimal background in coding, so we've had fantastic luck with non-CS folks :) With that said, the less background you have, the more motivation you'll need.

    By the end of the class you'll have learned how to comfortably do many things that may well seem like superpowers and could easily serve you well for the next few decades.

  2. If you have background in the "embedded" space, it's worth taking b/c you'll learn a bunch of useful but not widely-known tricks (I'll pay for your supplies and a pitcher of beer if this claim turns out to be false!)

  3. It's also super fun. The code you'll write can be used to as a basis for building many interesting systems.

    As one measure: Last year, I taught two extra follow-on classes (cs240lx and cs340lx) "for free" because of all the interesting things that came up from cs140e. In addition, it's caused me to write more code than I have since grad school. At my age, that's an unusual result :)

What this class is not

A quick skim might falsely pattern-match on a couple of things:

  1. cs140e is NOT an easier version of cs140. In fact, it can be quite a bit harder, since we work with raw hardware, and primarily use raw datasheets and ARMv6 architecture manuals rather than pre-digested text books or simulators.

    I'd say about 1/3 of the teaching evals from last year explicitly stated "do not take cs140e as an easier cs140".

    On the plus side, this approach is the adult way to do things, so you will be better prepared after the class for operating autonomously in the real world without safety nets or help. Everything you'll build will be stuff we personally found useful. There is no (intentional) busywork.

  2. Similarly, while we do use a raspberry pi for this class, and there are tons of blog posts/instructables/classes for novices showing how to use the r/pi to do simple things, this class is not that.

    You'll be writing virtual memory systems, SD card file systems, threads, i2c device drivers on raw hardware rather than cut-and-pasting some python on a library to blinky a light.

    We use the r/pi because its fairly cheap, holds up to electrical mistakes pretty well, runs a legit processor with legit hardware and is small enough to carry around easily.

With that said, I set aside the entire quarter to work on this course, so am happy to help people that need it --- some of the biggest success stories from past years were from students that had an initially large gap between their understanding and the topic but started to really "get it" after 4-5 weeks of struggle.

Lab policies.

  • You should be able to complete almost all of the lab in one sitting. If not, you must complete the lab within a week. We will not accept a lab after this.

  • To repeat: You must complete the lab within a week of it being issued.

  • PRELABS: Before each lab there will be some preparatory reading, which will typically include a short set of questions you need to answer and turn in before the lab begins. This is an attempt to make the labs more information-dense by handling basic stuff outside of it, and focusing mostly on any tricky details in it.

  • Labs are not optional! If you are going to miss a lab you need to make arrangements with us before hand, and missing more than one or two is going to affect your grade even if you turn in the work on time.

We had a more flexible policy in the past. Unfortunately, since labs typically build on each other, once people fell behind they got seriously lost. Further, this year we short-staffed for the amount of students taking the course, so don't have the resources to walk a few students each week through makeup labs.

Grading policy

Since we are short-staffed --- as are all Stanford lab classes for reasons I do not understand --- you are strongly encouraged to help other people! We will try to keep a note of who does so effectively, and will guarantee that you will be pushed up a grade if you are on the border.


  1. Prelabs must be completed before class, and labs must be completed within a week to receive credit.

  2. There will be three homeworks total, which will consist of integrating previous labs and submitting working code.

  3. Participation: Based on class attendance and discussion, and newsgroup replies. Students are allowed to miss 1-2 classes, but must notify the instructor beforehand.

What to do now.

First things first:

  1. Make arrangements to get the the hardware if you don't have already.

  2. clone the class repository:

    git clone

    You may need to install git, create a github account and register a key with github (if you don't want to do the latter, use the http clone method). See the our git instructions for more discussion.

  3. Make sure you have access to the cs140e newsgroup.
    Email us if not!

  4. Look in the docs directory to get a feel for what is there.

  5. Look in the labs directory and read through the labs 0 and 1 (we're adding them).

Previous Iterations:

Past years for reference: note that there is significant churn from year to year, and some of these labs relied heavily on in-person discussion to paper over quality issues with their writeups.


All material for CS140E, winter 2023.







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