SD Card

Hardware

The 305ap uses a native SDMMC1 (SDIO) interface for the microSD card, not a slower SPI emulation.

Signal	Pin
CMD	PD2
CLK	PC12
DAT0	PC8
DAT1	PC9
DAT2	PC10
DAT3	PC11
Card Detect	PE3

4-bit wide SDIO operation is supported, providing significantly higher throughput than SPI-mode SD cards. This is important for logging at high data rates without dropping log entries.

Card Requirements

Spec	Recommendation
Format	FAT32 (formatted by PX4 on first use if blank)
Capacity	4 GB – 32 GB recommended
Speed class	Class 10 or faster (UHS-I U1 minimum)
Type	microSD or microSDHC

Avoid very large cards (> 64 GB) as they typically use exFAT, which PX4 does not support. Cards larger than 32 GB must be reformatted to FAT32 before use.

Parameters require SD card

The 305ap has no FRAM. PX4 stores parameters at /fs/microsd/params. Without an SD card, parameter changes will not persist across reboots. Always insert a card before powering up.

PX4 SD Card Layout

After first boot with a blank card, PX4 creates the following directory structure:

/fs/microsd/
├── params          ← vehicle parameters
├── log/            ← flight logs (.ulg files)
│   └── YYYY-MM-DD/
│       └── HH-MM-SS.ulg
├── etc/            ← startup scripts (optional overrides)
└── missions/       ← saved missions

Logging

PX4 starts logging when:

• The vehicle is armed, or
• LOG_MODE is set to log always

Logs use the .ulg (ULog) format. They can be analyzed in:

• Flight Review (online)
• PlotJuggler with the ULog plugin
• QGroundControl → Analyze → Log Download

To download logs via QGC:

1. Connect via USB
2. Go to Analyze Tools → Log Download
3. Select and download logs to your computer

Verifying SD Card Detection

In the MAVLink Console:

ls /fs/microsd

If the SD card is detected and mounted, you will see the directory listing. A missing or unmounted card returns an error.

QGC will also show a warning in the status bar if no SD card is present.

Troubleshooting

Symptom	Likely cause	Fix
ls /fs/microsd fails	No card, or card not seated	Re-seat card; try a different card
Parameters reset on reboot	No card, or write errors	Check card health; reformat to FAT32
Logging stops mid-flight	Card full or write speed too slow	Use a faster card; free space on card
Card not recognized	exFAT format	Reformat to FAT32