libmodbus: initial version of the library

[mateuszkobak]

Modbus RTU master (client) library.

Description

Not all functionalities are implemented yet, but things that were needed for now should be there.

Motivation and Context

This was developed primarily for the use in Cognit Project.
See: https://github.com/SovereignEdgeEU-COGNIT/use-case-3-phoenix-demo

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (refactoring, style fixes, git/CI config, submodule management, no code logic changes)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: ia32-qemu, imxrt1170

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.

[github-actions]

Unit Test Results

9 277 tests  +63   8 687 ✅ +62   54m 33s ⏱️ +6s
  545 suites + 9     589 💤 ± 0 
    1 files   ± 0       1 ❌ + 1 

For more details on these failures, see this check.

Results for commit 2fed2d2. ± Comparison against base commit 82ac411.

♻️ This comment has been updated with latest results.

[anglov]

I put some early notes that will affect internal API and other small comment. To make a full review, I need dig a little deeper into it.

[anglov]

I am not convinced about way, how reading buffer works. I think it would be better to firstly read frame, and then do the things (in modbus RTU over serial, 3,5 bytes of no communication means end of frame. In your implementation you can always try to get more data, if you miss something.

On the other hand, it will be armored for bad server implementation, which doesn't respect timeouts. So I am not opposing on current situation for now. For me it's important, that read callback should always read whole frame. The rest are internal API, which can be subject of changes.

However I put some comment, that can armor your solution for communication error, and make this more readable.

[anglov]

Fine for me as for initial version. It's not a stable library (API will be subject of small changes when new features will be added), but I am ok to go for it for now.