This is more a brain dump for me in addition to the great resources already online.
First up go HERE https://openwrt.org/toh/bt/homehub_v5a
And HERE https://openwrt.ebilan.co.uk/viewtopic.php?f=7&t=266
You’ll need the Uboot image, LEDE boot image and the Sysupgrade image on a USB Stick. You’ll also have need to have done the UART mod detailed on the first page.
Assuming this is going on a live network you dont NEED to use 192.168.1.1 and the server address given. Ad the uboot prompt simply do:
U-Boot> setenv ipaddr 192.168.1.126
U-Boot> setenv serverip 192.168.1.1
U-Boot> setenv netmask 255.255.255.0
This sets us up using the IP addresses shown. This isn’t stored so if you screw up, you’ll have to start over.
Insert a fat32 formatted USB key into the USB port containing the squashfs image. Issue the following command to boot from your TFTP server
tftpboot 0x81000000 lede-lantiq-xrx200-BTHOMEHUBV5A-installimage.bin; bootm 0x81000000
Let it boot. When its done mount the USB stick and copy the image to /tmp
cp /mnt/usb/imagename.bin /tmp
mkdir /mnt/usb
mount /dev/sda1 /mnt/usb
Backup the NAND to USB…
nanddump -f /mnt/usb/3998.nanddump /dev/mtd4
This can take a while so go and do something else. I used the last 4 digits of the serial to name the file as I’ll do a few of these. Obviously junk flash drives will make this worse. Once its done, run the prepare script…
prepare
Allow it to do it’s thing and follow the prompts. Once its done we are ready to do the final install. Navigate to the usb drive you mounted and install the image. I had much more luck using the oldest image
sysupgrade /path/to/image/image.img
An important note here, and probobly a reason for a lot of reports of this failing. This will start, do a bit, complain about the watchdog, throw an error and then start running init scripts giving the opinion of a shutdown and halt. If you reboot at this point you’ll stuff the image. Unles it says “nand update failed”, leave it alone. The instructions don’t mention this and they do imply its a quick process. It takes a few minutes and then it WILL reboot back to the CFG prompt. Power cycle and you should be golden.