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EVT Caveats for Tachyon

This page documents the known issues and limitations of the EVT (Engineering Validation Test) version of the Tachyon board. Many of these will be addressed in DVT (Design Validation Test), but we encourage feedback from early testers to help refine these fixes.

Known Issues in EVT​

1/ Tachyon does not boot from USB power alone​

  • Issue: The board requires a battery to be always connected or powered via the 5V header. USB power alone is not sufficient.
  • Background: The software does not currently support utilizing the USB PD power supply only. We are working on a patch to resolve this.
  • Fix Status: No hardware fix is known at the moment.

2/ Battery charging is disabled when using an external 5V source via the 40-pin header​

  • Issue: The battery will not charge if the board is powered via the 40-pin 5V input.
  • Fix Status: This is a known EVT issue and will be resolved in DVT.

3/ 5V input/output selector header interferes with Raspberry Pi HATs​

  • Issue: The header is too high, physically interfering with RPi HATs.
  • Temporary Workaround: Bend the pins out of the way if necessary.
  • Fix Status: In DVT, this will be replaced with a DIP switch.

4/ Tachyon struggles to boot with a fully drained battery (even with USB-C plugged in)​

  • Issue: The board may fail to power on when the battery is fully drained, even with USB-C connected.
  • Fix Status: This is a software issue in EVT and a fix is in progress.
  • Workaround: Charge a completely dead battery using an existing 3-pin Particle developer board (e.g., Muon is recommended).

5/ Undervoltage protection circuit prevents boot-up in certain cases​

  • Issue: The circuit cuts off battery output until an external charge voltage is detected.
  • Background: Since the system controller detects battery presence via voltage measurement, it may falsely assume the battery is missing.
  • Fix Status: Investigating solutions for DVT.

6/ Audio recording level is too low​

  • Issue: The bias voltage is too low on EVT, leading to weak microphone input.
  • Fix Status: This will be fixed in DVT.

7/ LED color uniformity issues​

  • Issue: Some LEDs display incorrect colors (e.g., yellow appears too green).
  • Fix Status: In DVT, we will adjust the PWM resistors to improve LED color accuracy.

8/ I2C QWIIC header shares the same I2C bus as the 40-pin header​

  • Issue: The QWIIC header is not on a dedicated I2C bus.
  • Fix Status: In DVT, we will assign it to a separate bus.

9/ 5V power jumper markings are reversed​

  • Issue: The labels for IN and OUT are swapped.
  • Fix Status: This will be corrected in DVT. Apologies for the mistake!

10/ Test points missing for the second SIM interface​

  • Issue: No test points exist for SIM2, making validation harder.
  • Fix Status: We will add test points in DVT.

11/ Audio jack plug-in detection is unsupported​

  • Issue: The board does not detect when a headphone jack is inserted.
  • Fix Status: This will be added in DVT.

12/ PCIe logic level converter is too weak, causing resets​

  • Issue: Some PCIe boards reset unexpectedly due to insufficient drive strength.
  • Workaround: A temporary adapter is available for testing.
  • Fix Status: This will be fixed in DVT.

13/ Board gets too hot when charging​

  • Issue: The thermal management on EVT is insufficient, leading to overheating while charging.
  • Fix Status: We replaced a diode in DVT to resolve this.

14/ Antenna slightly extends beyond the PCB edge​

  • Issue: Some EVT boards have an antenna that sticks out, reducing compatibility with certain cases.
  • Fix Status: This will be corrected in DVT.

15/ USB 2 (host) port does not fully support USB-C hubs​

  • Issue: Missing pull-ups on the CC pins prevent some USB-C hubs from working.
  • Fix Status: This will be fixed in DVT.

16/ USB-C cable e-marker chip booster is missing​

  • Issue: The booster for the e-marker chip on USB-C cables is not populated in EVT.
  • Fix Status: This will be resolved in DVT.

17/ The Cellular connection may drop and reconnect on its own even if you have good signal.​

  • Issue: The cellular connection can drop due to a deep sleep bug and not reconnect.
  • Fix Status: Should have a fix out very soon!!

18/ Wi-Fi and WPA3.​

  • Issue: WPA3 doesn't work
  • Fix Status: For now, select WPA2 and it supports WPA2/WPA3. Fix is coming!

19/ Audio in Desktop.​

  • Issue: No audio output in Desktop mode
  • Fix Status: Currently, this is not supported by QCOM. A fix is due late May 2025

20/ Firefox Crash (and possibly some others apps).​

  • Issue: Firefox will randomly exit whilst running
  • Fix Status: TBD what this is - Chromium and other browswers work well. Still looking into this!

Additional Notes​

Reboot after flashing when installed the Desktop build​

The device remains in EDL mode post-flash. Manually power cycle the board to boot it.

USB connections for desktop mode​

Before powering on Tachyon in desktop mode, ensure the USB-C hub and HDMI display are connected. Otherwise, the device will remain in headless mode. We’re working on hotplug support.

First login delay​

The desktop may appear black for up to 5 seconds as it adjusts the display resolution. The system forces 1080p by default for compatibility. You can enable 4K manually.

Wi-Fi setup​

If Wi-Fi credentials are missing, use the menu to add them. For WPA3 networks, downgrade to WPA2 via the cog/settings icon until a future update enables full support.

Visual Studio Code command palette​

Use Shift + Ctrl + P to access commands. VS Code has a less traditional UI but excellent developer tooling.

Git authentication​

Git is installed but not authenticated. Users must add SSH keys or login credentials manually.

Desktop rendering performance​

Ubuntu 20.04 uses software rendering for some UI elements. This can feel sluggish under load. We plan to improve this with 22.04, but it cannot be backported.

⚠️ Note: Although Tachyon can operate at desktop speeds, upgrading to 22.04 now would result in loss of key features and stability.

VPN compatibility​

You can install VPN clients like WireGuard or others as needed for secure networking.

Next Steps​

We appreciate all feedback from EVT testers! If you encounter additional issues, please report them so we can ensure they are addressed in DVT.

Stay tuned for improvements in the next revision!