Meraki MR42 booting error

I am trying to install OpenWRT on a Cisco Meraki MR42 using the UART/TFTP recovery method from:

https://openwrt.org/toh/meraki/mr42

and:

https://github.com/openwrt/openwrt/commit/67f52012760ce553ba6393aaba77359a458deeda

What I have done so far:

  • Connected UART successfully at 115200 baud

  • Ubuntu host with static IP:
    192.168.1.250/24

  • Running tftpd-hpa

  • TFTP root is /srv/tftp

  • File present:
    openwrt-ipq806x-generic-meraki_mr42-initramfs-fit-uImage.itb

  • Used:
    sudo python3 ubootwrite.py --write=mr42_u-boot.bin

  • The script finishes with Done

  • UART output clearly shows:

    • U-Boot 2012.07-gb6f2d34-dirty

    • Cryptid Ramdisk

    • MR42 Device Tree

So the second-stage bootloader appears to be installed and booting correctly.

Current problem:

The AP never downloads the initramfs image from the TFTP server.

I do NOT see any TFTP RRQ requests in tcpdump or syslog.

However, during recovery/reset boot I DO see BOOTP/DHCP requests from the MR42 MAC address in tcpdump.

After that, the device falls back to booting the internal Meraki firmware instead of OpenWRT.

UART output eventually shows:

  • Bootkernel Meraki Build

  • Linux 4.4 Meraki kernel boot

  • Meraki CLI prompt <Meraki>

Can somebody help?

zero additional output over serial ?