🛠 Démarrage SD/USB et récupération d'une carte qui ne boot plus

Objectives

Master the Raspberry Pi 3 A+ boot chain: the "era" firmware (bootcode.bin / start.elf / config.txt) on the FAT partition, improved USB storage boot (3B+ generation OTP), and recovery of a card without tools like rpiboot — the 3 A+ does not have an EEPROM recovery mode like the Pi 4.

Hardware

• Raspberry Pi 3 A+; microSD ≥ 8 GB; USB drive formatted as FAT32/EXT4
• SD card reader on the PC; Raspberry Pi Imager
• >

Full code

# 1) Écrire l'image (la partition boot FAT apparaît montée après écriture)
sudo rpi-imager --cli img/raspios-lite.img /dev/sdX

# 2) Démarrage USB : écrire la MÊME image sur la clé, retirer la SD,
#    brancher la clé sur l'unique port USB puis alimenter.
#    (OTP USB boot de génération 3B+ ; sinon une première SD avec
#     le programme « raspberrypi-usb-boot » active le bit OTP.)

# 3) Récupération sans réécriture complète : la partition boot est lisible
#    sur tout PC — réparer config.txt (HDMI, dtoverlay) ou cmdline.txt :
sudo mount /dev/sdX1 /mnt && sudo nano /mnt/config.txt && sudo umount /mnt

# 4) Diagnostic matériel au power-on : les LED d'activité
#    LED rouge = alimentation ; LED verte clignotante = lecture SD.
vcgencmd version          # version du firmware chargé

Expected verification

With a valid SD card: the green LED blinks at power-on, then the system is available via SSH. Without an SD card and with a written USB drive: USB boot succeeds if the OTP is active. vcgencmd version responds with the firmware date.

Common errors

• Looking for an rpiboot/USB recovery mode: the 3 A+ does not have one (no VL805 EEPROM like the Pi 4); recovery involves rewriting or repairing the boot partition.
• Power-hungry USB drive: the single port, protected by a polyfuse, must power both the drive and the board; prefer a low-power USB drive.
• Editing config.txt on Windows with CRLF line endings: the FAT parser is tolerant, but editors sometimes break the encoding.
• SD card corrupted by a hard shutdown: run fsck on the root partition or rewrite the image — there is no secondary fallback storage on this model.