[Bug] I2C Bus Corruption with SD Card Inserted (Lightware LW20/C)

[mgardenswartz]

Describe the bug

Hardware Configuration:

• Flight Controller: CubePilot Blue
• Carrier Board: Standard ADS-B Carrier Board
• Firmware: PX4 v1.16.0 (Also confirmed on v1.15.0)
• Sensor: Lightware LW20/C (Firmware v4.4.3)
• Repeatability: 3 identical units verified exhibiting same behavior.

Issue 1: I2C Bus Corruption tied to SD Card Activity

The Lightware LW20/C (connected via I2C) exhibits severe data corruption when the MicroSD card is inserted.

Symptoms:

• min_distance toggles between 20 (valid) and 0.
• max_distance toggles between 10000 (valid) and 34364 (garbage).
• id toggles between 0 (valid) and 1 (garbage).
• current_distance flickers between an accurate measurement in centimeters and 20 (garbage)
• signal_quality spikes to 100 synchronously with garbage data.
• horizontal_fov flickers between 0 (valid) and 0.399902 (garbage).
• vertical_fov flickers between 0 (valid) and 0.399902 (garbage).

Reproduction Steps:

1. Connect LW20/C to I2C2 (as labeled on standard carrier).
2. Set SENS_EN_SF1XX to 6 (LW20/c).
3. Boot with SD Card Inserted: Data is unusable (flickering/garbage).
4. Boot with SD Card Removed: Data is perfect/stable.

Issue 2: UART Driver Protocol Mismatch (Secondary Issue) Attempting to switch to UART to mitigate the I2C noise results in a "Communication Error" loop.

Setup:

• Wiring: RX-to-TX and TX-to-RX (Verified).
• Baud: 115200 (Matched on Sensor and PX4).
• Params: SENS_SF0X_CFG = TELEM1 (or GPS1 or TELEM2, I tried each).

Symptoms:

• lightware_laser_serial status shows com_err count equal to read count (e.g., 429 reads, 429 errors). The number "429" is not consistent, but the number of reads always matches the number of com_errs.

This suggests the driver is receiving data but failing to parse the packets (like a Binary vs. ASCII protocol mismatch, but sf0x driver lacks a parameter to force the parsing mode). No setting in Lightware Studio appears to set the parsing mode.

Documentation Discrepancy:

The PX4 documentation for Cube Orange/Standard Carrier (here: https://docs.px4.io/main/en/flight_controller/cubepilot_cube_orange) incorrectly maps the I2C ports. On the physical board, the port labeled GPS1 is I2C1, and GPS2 is I2C2. (Source that matches real world observations: https://docs.cubepilot.org/user-guides/carrier-boards/cube-red-standard-carrier-board-pinout)

Troubleshooting Attempted:

• Moving between I2C1 and I2C2 (No change).
• Changing I2C bus frequency (No change).
• Replacing sensors and cables (No change).
• Only removing the SD card resolves the I2C issue.

Flight Log / Additional Information

N/A