# FreeRTOS Cellular Interface

## On this page:

- [Introduction](#Introduction)
- [Getting Started](#Getting-Started)
  - [Download the Source Code](#Download-the-Source-Code)
  - [Folder Structure](#Folder-Structure)
- [Implement Comm Interface with MCU Platforms](#Implement-Comm-Interface-with-MCU-Platforms)
- [Adding Support for New Cellular Modems](#Adding-Support-for-New-Cellular-Modems)
- [Integrate FreeRTOS Cellular Interface with Application](#Integrate-FreeRTOS-Cellular-Interface-with-Application)
- [Building Unit Tests](#Building-Unit-Tests)
- [Generating Documentation](#Generating-Documentation)
- [Contributing](#Contributing)

## Introduction

The Cellular Interface library implement a simple unified
[Application Programming Interfaces (APIs)](https://www.freertos.org/Documentation/api-ref/cellular/index.html)
that hide the complexity of AT commands. The cellular modems to be
interchangeable with the popular options built upon TCP stack and exposes a
socket-like interface to C programmers.

Most cellular modems implement more or less the AT commands defined by the
[3GPP TS v27.007](https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=1515)
standard. This project provides an implementation of such standard AT commands
in a
[reusable common component](https://github.com/FreeRTOS/FreeRTOS-Cellular-Interface/tree/main/source/include/common).
The three Cellular libraries in this project all take advantage of that common
code. The library for each modem only implements the vendor-specific AT
commands, then exposes the complete Cellular API.

The common component that implements the 3GPP TS v27.007 standard has been
written in compliance of the following code quality criteria:

- GNU Complexity scores are not over 8.
- MISRA coding standard. Any deviations from the MISRA C:2012 guidelines are
  documented in source code comments marked by "`coverity`".

**FreeRTOS Cellular Interface v1.4.0
[Source Code](https://github.com/FreeRTOS/FreeRTOS-Cellular-Interface/tree/v1.4.0/source)
is part of the
[FreeRTOS 202406.00 LTS](https://github.com/FreeRTOS/FreeRTOS-LTS/tree/202406.00-LTS)
release.**

## Getting Started

### Download the source code

To clone using HTTPS:

```
git clone https://github.com/FreeRTOS/FreeRTOS-Cellular-Interface.git
```

Using SSH:

```
git clone git@github.com/FreeRTOS/FreeRTOS-Cellular-Interface.git
```

### Folder structure

At the root of this repository are these folders:

- source : reusable common code that implements the standard AT commands defined
  by 3GPP TS v27.007.
- docs : documentations.
- test : unit test and cbmc.
- tools : tools for Coverity static analysis and CMock.

## Implement Comm Interface with MCU platforms

The FreeRTOS Cellular Interface runs on MCUs. It uses an abstracted interface -
the
[Comm Interface](https://github.com/FreeRTOS/FreeRTOS-Cellular-Interface/tree/main/source/interface/cellular_comm_interface.h),
to communicate with cellular modems. A Comm Interface must be implemented as
well on the MCU platform. The most common implementations of the Comm Interface
are over UART hardware, but it can be implemented over other physical interfaces
such as SPI as well. The documentation of the Comm Interface is found within the
[Cellular API References](https://www.freertos.org/Documentation/api-ref/cellular/cellular_porting.html#cellular_porting_comm_if).
These are example implementations of the Comm Interface:

- [FreeRTOS Windows Simulator Comm Interface](https://github.com/FreeRTOS/FreeRTOS/blob/main/FreeRTOS-Plus/Demo/FreeRTOS_Cellular_Interface_Windows_Simulator/Common/comm_if_windows.c)
- [FreeRTOS Common IO UART Comm Interface](https://github.com/aws/amazon-freertos/blob/feature/cellular/vendors/st/boards/stm32l475_discovery/ports/comm_if/comm_if_uart.c)
- [STM32 L475 Discovery Board Comm Interface](https://github.com/aws/amazon-freertos/blob/feature/cellular/vendors/st/boards/stm32l475_discovery/ports/comm_if/comm_if_st.c)
- [Sierra Sensor Hub Board Comm Interface](https://github.com/aws/amazon-freertos/blob/feature/cellular/vendors/sierra/boards/sensorhub/ports/comm_if/comm_if_sierra.c)

The FreeRTOS Cellular Interface uses kernel APIs for task synchronization and
memory management.

## Adding Support for New Cellular Modems

FreeRTOS Cellular Interface now supports AT commands, TCP offloaded Cellular
abstraction Layer. In order to add support for a new cellular modem, the
developer can use the
[common component](https://github.com/FreeRTOS/FreeRTOS-Cellular-Interface/tree/main/source/include/common)
that has already implemented the 3GPP standard AT commands.

In order to port the
[common component](https://www.freertos.org/Documentation/api-ref/cellular/cellular_porting_module_guide.html):

1. Implement the cellular modem porting interface defined in
   [cellular_common_portable.h](https://github.com/FreeRTOS/FreeRTOS-Cellular-Interface/tree/main/source/include/common/cellular_common_portable.h)
   ([Document](https://www.freertos.org/Documentation/api-ref/cellular/cellular__common__portable_8h.html)).
2. Implement the subset of Cellular Library APIs that use vendor-specific
   (non-3GPP) AT commands. The APIs to be implemented are the ones not marked
   with an "o" in
   [this table](https://www.freertos.org/Documentation/api-ref/cellular/cellular_common__a_p_is.html).
3. Implement Cellular Library callback functions that handle vendor-specific
   (non-3GPP) Unsolicited Result Code (URC). The URC handlers to be implemented
   are the ones not marked with an "o" in
   [this table](https://www.freertos.org/Documentation/api-ref/cellular/cellular_common__u_r_c_handlers.html).

The
[Cellular Common APIs document](https://www.freertos.org/Documentation/api-ref/cellular/cellular_porting_module_guide.html)
provides detail information required in each steps. It is recommended that you
start by cloning the implementation of one of the existing modems, then make
modifications where your modem's vendor-specific (non-3GPP) AT commands are
different.

Current Example Implementations:

- [Quectel BG96](https://github.com/FreeRTOS/FreeRTOS-Cellular-Interface-Reference-Quectel-BG96)
- [Sierra Wireless HL7802](https://github.com/FreeRTOS/FreeRTOS-Cellular-Interface-Reference-Sierra-Wireless-HL7802)
- [U-Blox Sara-R4](https://github.com/FreeRTOS/FreeRTOS-Cellular-Interface-Reference-ublox-SARA-R4)

## Integrate FreeRTOS Cellular Interface with Application

Once comm interface and cellular module implementation are ready, we can start
to integrate FreeRTOS Cellular Interface. The following diagram depicts the
relationship of these software components:

<p align="center"><img src="/docs/plantuml/images/cellular_components.svg" width="50%"><br>

Follow these steps to integrate FreeRTOS Cellular Interface into your project:

1. Clone this repository into your project.
2. Clone one of the reference cellular module implementations ( BG96 / HL7802 /
   SARA-R4 ) or create your own cellular module implementation in your project.
3. Implement comm interface.
4. Build these software components with your application and execute.

We also provide
[Demos for FreeRTOS-Cellular-Interface on Windows Simulator](https://github.com/FreeRTOS/FreeRTOS/tree/main/FreeRTOS-Plus/Demo/FreeRTOS_Cellular_Interface_Windows_Simulator)
as references for these three cellular modems example implementations.

## Building Unit Tests

### Checkout CMock Submodule

By default, the submodules in this repository are configured with `update=none`
in [.gitmodules](.gitmodules) to avoid increasing clone time and disk space
usage of other repositories (like
[FreeRTOS](https://github.com/FreeRTOS/FreeRTOS) that submodules this
repository).

To build unit tests, the submodule dependency of CMock is required. Use the
following command to clone the submodule:

```
git submodule update --checkout --init --recursive test/unit-test/CMock
```

### Platform Prerequisites

- For building the unit tests, **CMake 3.13.0** or later and a **C90 compiler**.
- For running unit tests, **Ruby 2.0.0** or later is additionally required for
  the CMock test framework (that we use).
- For running the coverage target, **gcov** and **lcov** are additionally
  required.

### Steps to build unit tests

1. Go to the root directory of this repository. (Make sure that the **CMock**
   submodule is cloned as described [above](#checkout-cmock-submodule).)

1. Run the _cmake_ command: `cmake -S test -B build`

1. Run this command to build the library and unit tests: `make -C build all`

1. The generated test executables will be present in `build/bin/tests` folder.

1. Run `cd build && ctest` to execute all tests and view the test run summary.

## CBMC

To learn more about CBMC and proofs specifically, review the training material
[here](https://model-checking.github.io/cbmc-training).

The `test/cbmc/proofs` directory contains CBMC proofs.

In order to run these proofs you will need to install CBMC and other tools by
following the instructions
[here](https://model-checking.github.io/cbmc-training/installation.html).

## Reference examples

Please refer to the demos of the Cellular Interface library
[here](https://github.com/FreeRTOS/FreeRTOS/tree/main/FreeRTOS-Plus/Demo/FreeRTOS_Cellular_Interface_Windows_Simulator)
using FreeRTOS on the Windows simulator platform. These can be used as reference
examples for the library API.

## Generating documentation

The Doxygen references were created using Doxygen version 1.9.6. To generate the
Doxygen pages, please run the following command from the root of this
repository:

```shell
doxygen docs/doxygen/config.doxyfile
```

## Contributing

See [CONTRIBUTING.md](./.github/CONTRIBUTING.md) for information on
contributing.
