more README
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README.md
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README.md
@ -4,3 +4,19 @@ FSFW From Zero Workshop
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This workshop gives an introduction to the Flight Software Framework,
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starting from a simple hello world program in C++. As such, it it also suitable
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for C++ beginners.
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Start by cloning this repository and updating the submodules to also clone
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the [Flight Software Framework](https://egit.irs.uni-stuttgart.de/fsfw):
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```sh
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git clone https://egit.irs.uni-stuttgart.de/fsfw/fsfw-from-zero.git
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git submodule init
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git submodule update
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```
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# Overview
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This workshop does an incremental build-up of a simple software which
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is similar to an On-Board Software.
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It is organised in chapters which have a task description.
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80
start/01-tasks.md
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80
start/01-tasks.md
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# Threads and Tasks
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A satellite is a complex system which usually has a lot of tasks which need to be done
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simulatenously by a dedicated On-Board Computer (OBC). This can include for example:
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- TMTC handling. This includes Telecommand (TC) reception and execution, and the (autonomous)
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generation of Telemetry (TM)
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- Control Operations, for example execution of the Attitue Control System (ACS) loop
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- Handling of connected physical devices like sensors or payloads
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Usually, these systems oftentimes have soft and even hard real-time requirements where longer delays
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are not allowed and the system has an upper bound for response times.
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This basically means that any software which does multiple non-trivial tasks needs a
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(real-time) operating system to perform multiple tasks consecutively, with deterministisc
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guarantees that these tasks are performed within a certain temporal bound.
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Some common operating system in the Space domain able to do this:
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- FreeRTOS for smaller MCUs (SOURCE)
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- Embedded Linux (EIVE)
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- RTEMS (FLP)
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All these operating system use threads or tasks as the basic worker unit which is executing code.
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This chapter first introduces threads as they are exposed by the C++ standard library.
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After that, the code is transitioned to use the abstraction provided by the framework.
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## 1. Scheduling a basic task using the C++ `std::thread` API
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The goal of this task is to set up a basic thread which prints the following
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string every second: "Executing Dummy Task".
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- [std::thread API](https://en.cppreference.com/w/cpp/thread/thread)
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- [Delaying a thread](https://en.cppreference.com/w/cpp/thread/sleep_for)
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## 2. Changing to the concept of executable objects
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Threads generally expect a function which is then directly executed.
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Sometimes, the execution of threads needs to be deferred. For example, this can be useful
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if the execution of tasks should only start after a certain condition.
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Also, it might become useful to model any task in form of a class. An instantiation
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of that class would then be an executable object. This is precisely what the framework
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exposes in form of the [`ExecutableObjectIF`](https://documentation.irs.uni-stuttgart.de/fsfw/development/api/task.html).
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It also offers a unform API to execute periodic tasks in form of the
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[`PeriodicTaskIF`](https://egit.irs.uni-stuttgart.de/fsfw/fsfw/src/branch/master/src/fsfw/tasks/PeriodicTaskIF.h).
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These tasks can then be created using the
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[`TaskFactory`](https://egit.irs.uni-stuttgart.de/fsfw/fsfw/src/branch/master/src/fsfw/tasks/TaskFactory.h) singleton.
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An arbitrary number of executable objects can then be passed to a periodic task. These objects
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are then executed sequentially. This allows a granular design of executable tasks.
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For example, important tasks get an own dedicated thread while other low priority objects are
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scheduled consecutively in another thread.
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The goal of this task is to convert the code from task 1 so the [std::thread]
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API takes an executable object to move to a more object oriented task approach.
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The printout of the threaf should remain the same.
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It is recommended to pass this executable object into the [std::thread] directly.
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- [std::reference_wrapper](https://en.cppreference.com/w/cpp/utility/functional/reference_wrapper)
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to pass referneces to the [std::thread] API.
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As a bonus task, you can make your executable object implement a
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[MyExecutableObjectIF] interface class. An interface class is
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an [abstract class](https://en.cppreference.com/w/cpp/language/abstract_class) which
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only contains pure virtual functions. As such, it can only be implemented by other
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objects and describes a certain API contract an object has to fulfill.
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## 3. Using the framework abstractions
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As described before, the framework provides task abstraction with some advantages
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- Task execution can be deferred until an explicit `start` method is called
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- Same uniform API for multiple operating systems
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The goal of this task is to implement the task specified in 1 using the
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abstractions provided in step 1.
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@ -1,11 +1,10 @@
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#include <iostream>
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#include "fsfw/serviceinterface.h"
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#include "FSFWConfig.h"
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#include "fsfw/FSFW.h"
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using namespace std;
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#if FSFW_CPP_OSTREAM_ENABLED == 1
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ServiceInterfaceStream sif::debug("DEBUG", false);
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ServiceInterfaceStream sif::info("INFO", false);
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@ -15,5 +14,4 @@ ServiceInterfaceStream sif::error("ERROR", false, true, true);
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int main() {
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cout << "hello world!" << endl;
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}
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