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Using OnAIR with core Flight System (cFS)

Overview

In order for OnAIR to receive cFS messages, cFS must include the Software Bus Network (SBN) app and the SBN Client library in its tree.

SBN is a cFS application that enables pub/sub across the software busses (SB) of multiple cFS instances: https://github.com/nasa/SBN

SBN Client is an external library that implements the SBN protocol. This allows other environments, including Python, to communicate with a Software Bus via the SBN: https://github.com/nasa/SBN-Client

In OnAIR, the sbn_adapter DataSource uses SBN Client to subscribe to messages on the Software Bus. When cFS messages are received, it extracts the data from the message structs and passes it up to the rest of the OnAIR system.

Example

An example distribution of cFS integrated with OnAIR can be found here.

In this example, OnAIR is configured to the subscribe to the sample_app house keeping telemetry packet, SAMPLE_APP_HkTlm_t.

Quick Start

Requirements: Docker

After cloning the repository, use docker compose to build and run a container called cfs-onair which should have both cFS and OnAIR dependencies set up.

docker compose up -d

After building, Docker will start the cfs-onair container in the background. Attach to the container using docker exec.

docker exec -it cfs-onair bash

Inside the cfs-onair container, use the build script to build cFS. SBN, SBN Client and OnAIR are added as cFS apps that will be built/installed by the cFS CMake system.

./_build.sh

Then navigate to the install directory and run cFS.

cd build/exe/cpu1
./core-cpu1

Open a new terminal. Then attach to the same cfs-onair container and navigate to the same intall directory.

docker exec -it cfs-onair bash
cd build/exe/cpu1

In this example, the build system copies OnAIR, the OnAIR telemetry metadata and config files, the ctypes structs of the cFS messages and the sbn_python_client python module from sbn_client files to cf/. The sbn-client.so binary is also installed to the cf/ directory.

Now OnAIR can be run from the install directory build/exe/cpu1.

python3 cf/onair/driver.py cf/onair/cfs_sample_app.ini

If OnAIR successfully connects to cFS via SBN Client and SBN, you should see the following start up log

SBN Adapter ignoring data file (telemetry should be live)
SBN Client library loaded: '<CDLL 'sbn_client.so', handle 11d7eef0 at 0xffff93b1f910>'
SBN_Client Connecting to 127.0.0.1, 2234

SBN Client init: 0
SBN Client command pipe: 0
SBN_Adapter Running
SBN Client subscribe msg (id 0x883): 0

***************************************************
************    SIMULATION STARTED     ************
***************************************************
App message received: MsgId 0x00000883
Payload: <message_headers.SAMPLE_APP_HkTlm_Payload_t object at 0xffff93ae7140>

Explanation

This repo is essentially the base distribution of cFS with three additional apps added, sbn, sbn_client and onair_app. While SBN_Client and OnAIR can exist outside of cFS as standalone projects, they were added as cFS apps to take advantage of the cFS build system.

SBN and SBN Client

SBN and SBN Client are added as submodules in the apps/ folder. They are added to the build system by appending them to the global app list found in the targets.cmake file. Since SBN is an actual cFS app it also needs to be added to the cfe start up script, cpu1-cfe_es_startup.scr. When SBN Client is built, it results in sbn-client.so binary that other processes, such as OnAIR, will use to communicate with the SBN.

By default, SBN's configuration table (sbn_conf_tbl.c) will assign the address and port 127.0.0.1:2234 to this instance of the SBN app. In order for SBN_Client to talk to SBN it must use the same address, which is set in sbn_client_defs.h.

OnAIR

An additional folder, called onair_app/ is also added to the apps/ folder. This folder contains the OnAIR source directory as a submodule, as well as a telemetry metadata file, config file, and a message_headers.py file. The onair_app also has a CMakeLists.txt file directing how it should be built by the cFS build system. In this case it just copies the files to the target directory.

s_o.ini - this is the config file. It specifies the name/location of the telemetry metadata file and selects sbn_adapter as the OnAIR Datasource.

s_o_TLM_CONFIG.json - this is the telemetry metadata file. It lists each data field that OnAIR is interested in as well as their order. Most importantly, in the channels field it matches the cFS message ID with name of the message and the name of the actual message struct. sbn_adapter will subscribe to the message IDs listed here. When a message is received sbn_adapter will use the received message IDs to determine the structure of the message so it can correctly unpack it.

    "channels":{
        "0x0883": ["SAMPLE_APP", "SAMPLE_APP_HkTlm_t"]
    }

message_headers.py - this python file is unqiue to sbn_adapter.py (i.e its not needed anywhere else in OnAIR). It defines the message structs that will be received using python ctypes. In this example message_headers.py contains the sample app house keeping message structs found in sample_app/fsw/src/sample_app_msg.h.