Beacon CM4 Agent Cheat Sheet

Automated Flash (jumper bridged, fully scripted)

One command — bridge the EMMC_DISABLE jumper, then run from repo root:

cd ~/repos/buildroot-beacon
./beacon-buildroot/scripts/flash-cm4.sh

The script:

Builds usbboot/rpiboot from source if not already compiled
Runs rpiboot -d mass-storage-gadget64 to expose eMMC over USB
Auto-detects the CM4 USB block device (~7.3 GiB)
Unmounts any auto-mounted partitions
Flashes output/images/sdcard.img.xz via bmaptool (sparse, fast)
Prints "Flash complete — remove jumper and power-cycle"

Override device explicitly if auto-detect picks wrong disk:

./beacon-buildroot/scripts/flash-cm4.sh /dev/sda

UART Console (interactive)

UART probe on GPIO14 (TX) / GPIO15 (RX), 115200 baud:

picocom -b 115200 /dev/ttyUSB1
# or with log capture:
picocom -b 115200 --logfile /tmp/uart-$(date +%s).log /dev/ttyUSB1

Exit: Ctrl-A Ctrl-X

UART Log Capture (non-interactive, agent-readable)

Use socat — truly headless, no terminal required, clean line endings:

# Start BEFORE power-cycling the CM4:
socat -u /dev/ttyUSB1,b115200,rawer,crnl OPEN:/tmp/uart-boot.log,creat,trunc &
# Stop capture after boot is done:
kill %1
# Read the log:
cat /tmp/uart-boot.log

Notes:

picocom backgrounded with & gets stopped by job control (SIGTTOU) — do not use it headlessly
cat /dev/ttyUSB1 with stty raw produces garbled output — do not use it

SSH Access

# Find CM4 IP (DHCP, changes on reboot):
ip neigh show dev enp0s31f6 | grep e4:5f:01:e9:13:96
# SSH:
sshpass -p beacon ssh user@<cm4-ip>

Note: Dropbear has no sftp-server — scp does NOT work. Transfer files via stdin pipe:

sshpass -p beacon ssh user@<cm4-ip> 'sudo tee /upload/rootfs.raucb > /dev/null' < output/images/rootfs.raucb

OTA Update (fully scripted from host)

CM4=10.11.0.xx  # find via: ip neigh show dev enp0s31f6

# 1. Transfer bundle (~51 MB, ~5s on LAN):
sshpass -p beacon ssh user@$CM4 'sudo tee /upload/rootfs.raucb > /dev/null' \
  < output/images/rootfs.raucb

# 2. Install:
sshpass -p beacon ssh user@$CM4 'rauc install /upload/rootfs.raucb'

# 3. Reboot into slot B:
sshpass -p beacon ssh user@$CM4 'sudo reboot'

# 4. After reboot (new IP — find again with ip neigh):
sshpass -p beacon ssh user@$CM4_NEW 'rauc status mark-good && rauc status'

Note: ports 8080 and 9090 are taken by other host services — do NOT use HTTP for OTA.

RAUC Status

sshpass -p beacon ssh user@<cm4-ip> 'rauc status'
sudo fw_printenv | grep BOOT_

Rescue Mode

Short GPIO4 (pin 7) to GND (pin 9) on 40-pin header during power-on.

Secure Boot Provision (Milestone 2)

update-pieeprom.sh -k private.pem
rpiboot -d secure-boot-recovery

rpi secure boot private key: use /buildroot-beacon/private.pem — do NOT generate a fresh one. RAUC has its own key; keep both alongside each other.

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