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@ -23,7 +23,7 @@ This project currently contains following crates:
on a host computer or on any system with a standard runtime like a Raspberry Pi.
* [`satrs-mib`](https://egit.irs.uni-stuttgart.de/rust/satrs-launchpad/src/branch/main/satrs-mib):
Components to build a mission information base from the on-board software directly.
* [`satrs-example-stm32f3-disco`](https://egit.irs.uni-stuttgart.de/rust/satrs-example-stm32f3-disco):
* [`satrs-example-stm32f3-disco`](https://egit.irs.uni-stuttgart.de/rust/sat-rs/src/branch/main/satrs-example-stm32f3-disco):
Example of a simple example on-board software using sat-rs components on a bare-metal system
with constrained resources.

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book

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[book]
authors = ["Robin Mueller"]
language = "en"
multilingual = false
src = "src"
title = "The sat-rs book"

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# Summary
- [Introduction](./introduction.md)
- [Design](./design.md)
- [Communication with Space Systems](./communication.md)
- [Working with Constrained Systems](./constrained-systems.md)
- [Actions](./actions.md)
- [Modes and Health](./modes-and-health.md)
- [Housekeeping Data](./housekeeping.md)
- [Events](./events.md)
- [Power Components](./power.md)
- [Thermal Components](./thermal.md)
- [Persistent TM storage](./persistent-tm-storage.md)
- [FDIR](./fdir.md)
- [Serialization of Data](./serialization.md)
- [Logging](./logging.md)
- [Modelling space systems](./modelling-space-systems.md)
- [Ground Segments](./ground-segments.md)

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# Working with Actions
Space systems generally need to be commanded regularly. This can include commands periodically
required to ensure a healthy system, or commands to reach the mission goals.
These commands can be modelled using the concept of Actions. the ECSS PUS standard also provides
the PUS service 8 for actions, but provides few concrete subservices and specification on how
action commanding could look like.
`sat-rs` proposes two recommended ways to perform action commanding:
1. Target ID and Action ID based. The target ID is a 32-bit unsigned ID for an OBSW object entity
which can also accept Actions. The action ID is a 32-bit unsigned ID for each action that a
target is able to perform.
2. Target ID and Action String based. The target ID is the same as in the first proposal, but
the unique action is identified by a string.
The framework provides an `ActionRequest` abstraction to model both of these cases.
## Commanding with ECSS PUS 8
`sat-rs` provides a generic ECSS PUS 8 action command handler. This handler can convert PUS 8
telecommands which use the commanding scheme 1 explained above to an `ActionRequest` which is
then forwarded to the target specified by the Target ID.
There are 3 requirements for the PUS 8 telecommand:
1. The subservice 128 must be used
2. Bytes 0 to 4 of application data must contain the target ID in `u32` big endian format.
3. Bytes 4 to 8 of application data must contain the action ID in `u32` big endian format.
4. The rest of the application data are assumed to be command specific additional parameters. They
will be added to an IPC store and the corresponding store address will be sent as part of the
`ActionRequest`.
## Sending back telemetry
There are some cases where the regular verification provided by PUS in response to PUS action
commands is not sufficient and some additional telemetry needs to be sent to ground. In that
case, it is recommended to chose some custom subservice for action TM data and then send the
telemetry using the same scheme as shown above, where the first 8 bytes of the application
data is reserved for the target ID and action ID.

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# Communication with sat-rs based software
Communication is a huge topic for space systems. Remote systems are usually not (directly)
connected to the internet and only have 1-2 communication links during nominal operation. However,
most of these systems have internet access during development cycle. There are various standards
provided by CCSDS and ECSS which can be useful to determine how to communicate with the satellite
and the primary On-Board Software.
# Application layer
Most communication with space systems is usually packet based. For example, the CCSDS space
packet standard only specifies a 6 byte header with at least 1 byte payload. The PUS packet
standard is a subset of the space packet standard, which adds some fields and a 16 bit CRC, but
it is still centered around small packets. `sat-rs` provides support for these ECSS and CCSDS
standards and also attempts to fill the gap to the internet protocol by providing the following
components.
1. [UDP TMTC Server](https://docs.rs/satrs-core/0.1.0-alpha.0/satrs_core/hal/host/udp_server/index.html#).
UDP is already packet based which makes it an excellent fit for exchanging space packets.
2. TCP TMTC Server. This is a stream based protocol, so the server uses the COBS framing protocol
to always deliver complete packets.
# Working with telemetry and telecommands (TMTC)
The commands sent to a space system are commonly called telecommands (TC) while the data received
from it are called telemetry (TM). Keeping in mind the previous section, the concept of a TC source
and a TM sink can be applied to most satellites. The TM sink is the one entity where all generated
telemetry arrives in real-time. The most important task of the TM sink usually is to send all
arriving telemetry to the ground segment of a satellite mission immediately. Another important
task might be to store all arriving telemetry persistently. This is especially important for
space systems which do not have permanent contact like low-earth-orbit (LEO) satellites.
The most important task of a TC source is to deliver the telecommands to the correct recipients.
For modern component oriented software using message passing, this usually includes staged
demultiplexing components to determine where a command needs to be sent.
# Low-level protocols and the bridge to the communcation subsystem
Many satellite systems usually use the lower levels of the OSI layer in addition to the application
layer covered by the PUS standard or the CCSDS space packets standard. This oftentimes requires
special hardware like dedicated FPGAs to handle forward error correction fast enough. `sat-rs`
might provide components to handle standard like the Unified Space Data Link Standard (USLP) in
software but most of the time the handling of communication is performed through custom
software and hardware. Still, connecting this custom software and hardware to `sat-rs` can mostly
be done by using the concept of TC sources and TM sinks mentioned previously.

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# Working with Constrained Systems
Software for space systems oftentimes has different requirements than the software for host
systems or servers. Currently, most space systems are considered embedded systems.
For these systems, the computation power and the available heap are the most important resources
which are constrained. This might make completeley heap based memory management schemes which
are oftentimes used on host and server based systems unfeasable. Still, completely forbidding
heap allocations might make software development unnecessarilly difficult, especially in a
time where the OBSW might be running on Linux based systems with hundreds of MBs of RAM.
A useful pattern used commonly in space systems is to limit heap allocations to program
initialization time and avoid frequent run-time allocations. This prevents issues like
running out of memory (something even Rust can not protect from) or heap fragmentation.
# Using pre-allocated pool structures
A huge candidate for heap allocations is the TMTC and handling. TC, TMs and IPC data are all
candidates where the data size might vary greatly. The regular solution for host systems
might be to send around this data as a `Vec<u8>` until it is dropped. `sat-rs` provides
another solution to avoid run-time allocations by offering and recommendng pre-allocated static
pools.
These pools are split into subpools where each subpool can have different page sizes.
For example, a very small TC pool might look like this:
TODO: Add image
A TC entry inside this pool has a store address which can then be sent around without having
to dynamically allocate memory. The same principle can also be applied to the TM and IPC data.
# Using special crates to prevent smaller allocations
Another common way to use the heap on host systems is using containers like `String` and `Vec<u8>`
to work with data where the size is not known beforehand. The most common solution for embedded
systems is to determine the maximum expected size and then use a pre-allocated `u8` buffer and a
size variable. Alternatively, you can use the following crates for more convenience or a smart
behaviour which at the very least reduce heap allocations:
1. [`smallvec`](https://docs.rs/smallvec/latest/smallvec/).
2. [`arrayvec`](https://docs.rs/arrayvec/latest/arrayvec/index.html) which also contains an
[`ArrayString`](https://docs.rs/arrayvec/latest/arrayvec/struct.ArrayString.html) helper type.
3. [`tinyvec`](https://docs.rs/tinyvec/latest/tinyvec/).
# Using a fixed amount of threads
On host systems, it is a common practice to dynamically spawn new threads to handle workloads.
On space systems this is generally considered an anti-pattern as this is considered undeterministic
and might lead to similar issues like when dynamically using the heap. For example, spawning a new
thread might use up the remaining heap of a system, leading to undeterministic errors.
The most common way to avoid this is to simply spawn all required threads at program initialization
time. If a thread is done with its task, it can go back to sleeping regularly, only occasionally
checking for new jobs. If a system still needs to handle bursty concurrent loads, another possible
way commonly used for host systems as well would be to use a threadpool, for example by using the
[`threadpool`](https://crates.io/crates/threadpool) crate.

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# Framework Design
Satellites and space systems in general are complex systems with a wide range of requirements for
both the hardware and the software. Consequently, the general design of the framework is centered
around many light-weight components which try to impose as few restrictions as possible on how to
solve certain problems.
There are still a lot of common patterns and architectures across these systems where guidance
of how to solve a problem and a common structure would still be extremely useful to avoid pitfalls
which were already solved and to avoid boilerplate code. This framework tries to provide this
structure and guidance the following way:
1. Providing this book which explains the architecture and design patterns in respect to common
issues and requirements of space systems.
2. Providing an example application. Space systems still commonly have large monolithic
primary On-Board Softwares, so the choice was made to provide one example software which
contains the various features provided by sat-rs.
3. Providing a good test suite. This includes both unittests and integration tests. The integration
tests can also serve as smaller usage examples than the large `satrs-example` application.
This framework has special support for standards used in the space industry. This especially
includes standards provided by Consultative Committee for Space Data Systems (CCSDS) and European
Cooperation for Space Standardization (ECSS). It does not enforce using any of those standards,
but it is always recommended to use some sort of standard for interoperability.
A lot of the modules and design considerations are based on the Flight Software Framework (FSFW).
The FSFW has its own [documentation](https://documentation.irs.uni-stuttgart.de/fsfw/), which
will be referred to when applicable. The FSFW was developed over a period of 10 years for the
Flying Laptop Project by the University of Stuttgart with Airbus Defence and Space GmbH.
It has flight heritage through the 2 mssions [FLP](https://www.irs.uni-stuttgart.de/en/research/satellitetechnology-and-instruments/smallsatelliteprogram/flying-laptop/)
and [EIVE](https://www.irs.uni-stuttgart.de/en/research/satellitetechnology-and-instruments/smallsatelliteprogram/EIVE/).
Therefore, a lot of the design concepts were ported more or less unchanged to the `sat-rs`
framework.
FLP is a medium-size small satellite with a higher budget and longer development time than EIVE,
which allowed to build a highly reliable system while EIVE is a smaller 6U+ cubesat which had a
shorter development cycle and was built using cheaper COTS components. This framework also tries
to accumulate the knowledge of developing the OBSW and operating the satellite for both these
different systems and provide a solution for a wider range of small satellite systems.
`sat-rs` can be seen as a modern port of the FSFW which uses common principles of software
engineering to provide a reliable and robust basis for space On-Board Software. The choice
of using the Rust programming language was made for the following reasons:
1. Rust has safety guarantees which are a perfect fit for space systems which generally have high
robustness and reliablity guarantees.
2. Rust is suitable for embedded systems. It can also be run on smaller embedded systems like the
STM32 which have also become common in the space sector. All space systems are embedded systems,
which makes using large languages like Python challenging even for OBCs with more performance.
3. Rust has support for linking C APIs through its excellent FFI support. This is especially
important because many vendor provided libaries are still C based.
4. Modern tooling like a package managers and various development helper, which can further reduce
development cycles for space systems. `cargo` provides tools like auto-formatters and linters
which can immediately ensure a high software quality throughout each development cycle.
5. A large ecosystem with excellent libraries which also leverages the excellent tooling provided
previously. Integrating these libraries is a lot easier compared to languages like C/C++ where
there is still no standardized way to use packages.

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# Events
Events can be an extremely important mechanism used for remote systems to monitor unexpected
or expected anomalies and events occuring on these systems. They are oftentimes tied to
Fault Detection, Isolation and Recovery (FDIR) operations, which need to happen autonomously.
Events can also be used as a convenient Inter-Process Communication (IPC) mechansism, which is
also observable for the Ground segment. The PUS Service 5 standardizes how the ground interface
for events might look like, but does not specify how other software components might react
to those events. There is the PUS Service 19, which might be used for that purpose, but the
event components recommended by this framework do not really need this service.
The following images shows how the flow of events could look like in a system where components
can generate events, and where other system components might be interested in those events:
![Event flow](images/event_man_arch.png)

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# Fault Detecion, Isolation And Recovery (FDIR)

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# Ground Segments

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# Housekeeping Data
Remote systems like satellites and rovers oftentimes generate data autonomously and periodically.
The most common example for this is temperature or attitude data. Data like this is commonly
referred to as housekeeping data, and is usually one of the most important and most resource heavy
data sources received from a satellite. Standards like the PUS Service 3 make recommendation how to
expose housekeeping data, but the applicability of the interface offered by PUS 3 has proven to be
partially difficult and clunky for modular systems.
First, we are going to list some assumption and requirements about Housekeeping (HK) data:
1. HK data is generated periodically by various system components throughout the
systems.
2. An autonomous and periodic sampling of that HK data to be stored and sent to Ground is generally
required. A minimum interface consists of requesting a one-shot sample of HK, enabling and
disabling the periodic autonomous generation of samples and modifying the collection interval
of the periodic autonomous generation.
3. HK data often needs to be shared to other software components. For example, a thermal controller
wants to read the data samples of all sensor components.
A commonly required way to model HK data in a clean way is also to group related HK data into sets,
which can then dumped via a similar interface.
TODO: Write down `sat-rs` recommendations how to expose and work with HK data.

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The sat-rs book
======
This book is the primary information resource for the [sat-rs framework](https://egit.irs.uni-stuttgart.de/rust/sat-rs)
in addition to the regular API documentation. It contains the following resources:
1. Architecture informations and consideration which would exceeds the scope of the regular API.
2. General information on how to build On-Board Software and how `sat-rs` can help to fulfill
the unique requirements of writing software for remote systems.
2. A Getting-Started workshop where a small On-Board Software is built from scratch using
sat-rs components.
# Introduction
The primary goal of the sat-rs framework is to provide re-usable components
to write on-board software for remote systems like rovers or satellites. It is specifically written
for the special requirements for these systems.
A lot of the architecture and general design considerations are based on the
[FSFW](https://egit.irs.uni-stuttgart.de/fsfw/fsfw) C++ framework which has flight heritage
through the 2 missions [FLP](https://www.irs.uni-stuttgart.de/en/research/satellitetechnology-and-instruments/smallsatelliteprogram/flying-laptop/)
and [EIVE](https://www.irs.uni-stuttgart.de/en/research/satellitetechnology-and-instruments/smallsatelliteprogram/EIVE/).

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# Logging

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# Modelling Space Systems

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# Modes
Modes are an extremely useful concept for complex system in general. They also allow simplified
system reasoning for both system operators and OBSW developers. They model the behaviour of a
component and also provide observability of a system. A few examples of how to model
different components of a space system with modes will be given.
## Modelling a pyhsical devices with modes
The following simple mode scheme with the following three mode
- `OFF`
- `ON`
- `NORMAL`
can be applied to a large number of simpler devices of a remote system, for example sensors.
1. `OFF` means that a device is physically switched off, and the corresponding software component
does not poll the device regularly.
2. `ON` means that a device is pyhsically switched on, but the device is not polled perically.
3. `NORMAL` means that a device is powered on and polled periodically.
If a devices is `OFF`, the device handler will deny commands which include physical communication
with the connected devices. In `NORMAL` mode, it will autonomously perform periodic polling
of a connected physical device in addition to handling remote commands by the operator.
Using these three basic modes, there are two important transitions which need to be taken care of
for the majority of devices:
1. `OFF` to `ON` or `NORMAL`: The device first needs to be powered on. After that, the
device initial startup configuration must be performed.
2. `NORMAL` or `ON` to `OFF`: Any important shutdown configuration or handling must be performed
before powering off the device.
## Modelling a controller with modes
Controller components are not modelling physical devices, but a mode scheme is still the best
way to model most of these components.
For example, a hypothetical attitude controller might have the following modes:
- `SAFE`
- `TARGET IDLE`
- `TARGET POINTING GROUND`
- `TARGET POINTING NADIR`
We can also introduce the concept of submodes: The `SAFE` mode can for example have a
`DEFAULT` submode and a `DETUMBLE` submode.
## Achieving system observability with modes
If a system component has a mode in some shape or form, this mode should be observable. This means
that the operator can also retrieve the mode for a particular component. This is especially
important if these components can change their mode autonomously.
If a component is able to change its mode autonomously, this is also something which is relevant
information for the operator or for other software components. This means that a component
should also be able to announce its mode.
This concept becomes especially important when applying the mode concept on the whole
system level. This will also be explained in detail in a dedicated chapter, but the basic idea
is to model the whole system as a tree where each node has a mode. A new capability is added now:
A component can announce its mode recursively. This means that the component will announce its
own mode first before announcing the mode of all its children. Using a scheme like this, the mode
of the whole system can be retrieved using only one command. The same concept can also be used
for commanding the whole system, which will be explained in more detail in the dedicated systems
modelling chapter.
In summary, a component which has modes has to expose the following 4 capabilities:
1. Set a mode
2. Read the mode
3. Announce the mode
4. Announce the mode recursively
## Using ECSS PUS to perform mode commanding
# Health
Health is an important concept for systems and components which might fail.
Oftentimes, the health is tied to the mode of a system component in some shape or form, and
determines whether a system component is usable. Health is also an extremely useful concept
to simplify the Fault Detection, Isolation and Recovery (FDIR) concept of a system.
The following health states are based on the ones used inside the FSFW and are enough to model most
use-cases:
- `HEALTHY`
- `FAULTY`
- `NEEDS RECOVERY`
- `EXTERNAL CONTROL`
1. `HEALTHY` means that a component is working nominally, and can perform its task without any issues.
2. `FAULTY` means that a component does not work properly. This might also impact other system
components, so the passivation and isolation of that component is desirable for FDIR purposes.
3. `NEEDS RECOVERY` is used to attempt a recovery of a component. For example, a simple sensor
could be power-cycled if there were multiple communication issues in the last time.
4. `EXTERNAL CONTROL` is used to isolate an individual component from the rest of the system. For
example, on operator might be interested in testing a component in isolation, and the interference
of the system is not desired. In that case, the `EXTERNAL CONTROL` health state might be used
to prevent mode commands from the system while allowing external mode commands.

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# Persistent Telemetry (TM) Storage

1
satrs-book/src/power.md Normal file
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# Power Components

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# Serialization

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# Thermal Components

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@ -51,9 +51,9 @@ use std::vec::Vec;
/// .expect("Error sending PUS TC via UDP");
/// ```
///
/// The [fsrc-example crate](https://egit.irs.uni-stuttgart.de/rust/fsrc-launchpad/src/branch/main/fsrc-example)
/// The [satrs-example crate](https://egit.irs.uni-stuttgart.de/rust/fsrc-launchpad/src/branch/main/-example)
/// server code also includes
/// [example code](https://egit.irs.uni-stuttgart.de/rust/fsrc-launchpad/src/branch/main/fsrc-example/src/bin/obsw/tmtc.rs)
/// [example code](https://egit.irs.uni-stuttgart.de/rust/sat-rs/src/branch/main/satrs-example/src/tmtc.rs#L67)
/// on how to use this TC server. It uses the server to receive PUS telecommands on a specific port
/// and then forwards them to a generic CCSDS packet receiver.
pub struct UdpTcServer<E> {