Reduce T-Echo firmware footprint to preserve future flash headroom

[mviotti]

Remove the unused BME68x Sensor library from the T-Echo build. The T-Echo only supports the BME280 sensor, so including the BME68x library provides no functional benefit while consuming a significant amount of flash.

Results

Flash usage:

Before: 93.8% (764440 / 815104 bytes)
After: 88.6% (721792 / 815104 bytes)
This reclaims approximately 43 KB of flash (~5% of the available program memory), providing additional headroom for future features and reducing the risk of the T-Echo exceeding its flash limit as the firmware continues to evolve.

Build output before this change:

RAM:   [====      ]  37.5% (used 93212 bytes from 248832 bytes)
Flash: [========= ]  93.8% (used 764440 bytes from 815104 bytes)

Build output after this change:

RAM:   [====      ]  35.8% (used 89004 bytes from 248832 bytes)
Flash: [========= ]  88.6% (used 721792 bytes from 815104 bytes)

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for the t-echo-inkhud version, there is also an improvement (this version was also tested):
Before the changes:

RAM:   [===       ]  33.9% (used 84372 bytes from 248832 bytes)
Flash: [========= ]  88.4% (used 720160 bytes from 815104 bytes)

After the changes:

RAM:   [===       ]  31.9% (used 79356 bytes from 248832 bytes)
Flash: [========  ]  82.7% (used 673904 bytes from 815104 bytes)

🤝 Attestations

• I have tested that my proposed changes behave as described.
• I have tested that my proposed changes do not cause any obvious regressions on the following devices:
  • Heltec (Lora32) V3
  • LilyGo T-Deck
  • LilyGo T-Beam
  • RAK WisBlock 4631
  • Seeed Studio T-1000E tracker card
  • Other (please specify below)
  • LilyGo T-Echo

Summary by CodeRabbit

• Chores
  • Improved T-Echo firmware build configuration.
  • Prevented unsupported sensor libraries from being included in T-Echo builds, helping ensure more reliable compilation and device firmware generation.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 5d0cc1cb-3d32-40c5-bb37-57cf22c557a1

📥 Commits

Reviewing files that changed from the base of the PR and between 58657d4 and b8b9391.

📒 Files selected for processing (1)

• variants/nrf52840/t-echo/platformio.ini

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📝 Walkthrough

Walkthrough

The PlatformIO configuration adds inherited NRF52840 library exclusions and excludes bsec2 and the BME68x Sensor library from both T-Echo environments.

Changes

T-Echo library configuration

Layer / File(s)	Summary
Configure T-Echo exclusions variants/nrf52840/t-echo/platformio.ini	Both T-Echo environments inherit the NRF52840 ignore list and exclude BSEC2 and the BME68x Sensor library.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Suggested reviewers: vidplace7

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the primary change: reducing T-Echo firmware size to preserve flash capacity.
Description check	✅ Passed	The description explains the change, reports measured results, and documents testing on the affected T-Echo hardware.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[github-actions]

@mviotti, Welcome to Meshtastic!

Thanks for opening your first pull request. We really appreciate it.

We discuss work as a team in discord, please join us in the #firmware channel.
There's a big backlog of patches at the moment. If you have time,
please help us with some code review and testing of other PRs!

Welcome to the team 😄

[NomDeTom]

I don't think we are actually struggling for flash on this target - NRF pro-micro is at 98% and works.

Even if we were, this is not the way to recover flash - we would make a wider change than cherry picking specific devices.

[NomDeTom]

This isn't the way to recover flash, and it's not causing a specific problem.

[mviotti]

Hi @NomDeTom, thanks for the fedback. I will keep it in mind for further contributions.
I will close this branch.