Spi Flash

spi-flash

Use when UART is unavailable, or a full firmware extraction/patching loop is required.

1. Identification and connection

• Look for 8-pin or 16-pin SOIC chips near the SoC (e.g., Winbond W25Q*, Macronix MX25L* or GigaDevice GD25Q*).
• In-circuit: Attach a SOIC clip. Ensure the target board is completely powered off to prevent SoC interference.
• Out-of-circuit: Desolder using hot air, clean pads, mount in programming socket. (Safest for signal integrity, but destructive).

2. Reading firmware (flashrom)

Rule: Read at least twice, and ensure hashes match before proceeding. Variance indicates bad clip contact or SoC contention.

# Read attempt 1
flashrom -p ch341a_spi -r fw_dump1.bin

# Read attempt 2
flashrom -p ch341a_spi -r fw_dump2.bin

# Verification
md5sum fw_dump1.bin fw_dump2.bin

If hashes differ, reseat the clip, shorten cables, or power the target board VCC slightly if SoC is draining programmer current.

3. Writing firmware

Rule: Always backup original raw dump offline before writing.

# Write modified firmware back
flashrom -p ch341a_spi -w fw_patched.bin

4. Flash layout verification

Use binwalk to verify the read was successful and contains expected headers (not just 0xFF or 0x00).

binwalk fw_dump1.bin
# Expect: U-Boot header, Squashfs, JFFS2, TRX, or CramFS

References

• references/ch341a-voltage-fix.md — Load when using a CH341A programmer on 1.8V or 3.3V target flash chips.