Debugging

Serial console

The primary console is UART0 on the f1c200s, exposed on the board's UART header. Baud rate is 115200 8N1.

Linux:

picocom -b 115200 /dev/ttyUSB0

macOS:

picocom -b 115200 /dev/tty.usbserial-FTA02VH8

The console shows U-Boot output and the Linux boot log, and gives you a login prompt (root / root).

USB Ethernet gadget

g_ether is configured in the rootfs, so as soon as Linux is up the device exposes itself as a USB Ethernet adapter:

• Device address: 192.168.2.2
• Host address: assign 192.168.2.1/24 to the corresponding host interface

ssh root@192.168.2.2

The MAC address is announced at boot; for example:

g_ether gadget.0: HOST MAC 22:84:d6:6a:6c:8f
g_ether gadget.0: MAC 5a:6c:c6:09:0f:dd

If the gadget never enumerates, look for this in the kernel log:

UDC core: g_ether: couldn't find an available UDC

It usually means the USB OTG controller is held by something else (musb host mode, etc.) — check the DTS and usb_phy_generic.

Mass storage gadget

There is an experimental setup using g_mass_storage. Status: not currently functional but kept as a reference.

modprobe g_mass_storage iSerialNumber=123456 file=/mnt/fat32.part stall=0 removable=1
losetup /dev/loop0 /mnt/fat32.part

Common errors

Symptom	Cause / Fix
System reset not supported on this platform in U-Boot	Watchdog reset support missing in U-Boot defconfig — enable it and rebuild.
Wrong Image Type for bootm command	Use the FIT image (image.its / *.itb) instead of legacy uImage.
UBIFS error: LEB size mismatch: 129024 in superblock, 126976 real	Buildroot UBIFS LEB size differs from the runtime UBI device. See SPI NAND Partitioning.
ubi: mtd1 is already attached to ubi0	The volume is still attached from a previous attempt. ubidetach -p /dev/mtd1 first.
failed to load regulatory.db	Cosmetic — the Wi-Fi regulatory DB blob is not shipped; safe to ignore.
SPI driver fb_ili9340 has no spi_device_id for ilitek,ili9340	Optional LCD probe; cosmetic if you do not use the display.
Failed to request TX DMA channel on sun6i-spi	f1c200s DMA is not supported in mainline — SPI falls back to PIO automatically.

Boot time

Measured 16/06/2024: cold boot to login ≈ 24 s, of which:

• ~1 s: SPL + U-Boot
• ~7 s: U-Boot kernel/DTB loading
• ~16 s: kernel + UBI attach + UBIFS recovery + userspace

The dominating chunks are UBI scan (~0.8 s) and uImage load from UBIFS (~3.7 s). Improvements likely come from fastmap and from trimming the kernel image.

PS1

A coloured prompt that has proved useful in long debug sessions:

PS1='\[\e[0;31m\]\u\[\e[m\] \[\e[0;32m\]\h\[\e[m\]@\[\e[0;34m\]\w\[\e[m\]\$ '