16M/64M upgrade was successful. My devices are running with 16MB flash and 64MB RAM now. One with latest OpenWrt and one with gluon (Freifunk Stuttgart firmware).
I used the following devices:
RAM: Hynix HY5DU121622DTP-D43
Flash: Winbond 25Q128FVSG
Ram upgrade procedure:
- Desolder old RAM
- Solder new RAM
- Now test the device. If you soldered the ram correctly, it works as before.
- RAM size is hard coded in boot loader. To use the 64M you need to flash a modified boot loader. Either
a) use a modified OpenWrt image (with boot partition writable) and write it from OpenWrt
b) use serial console and flash with u-boot and tftp
I will upload modified u-boot binary and source later.
Flash upgrade is easier to solder but more firmware changes:
- Save your ART partition. It is individual for every hardware.
- Desolder old Flash
- Write bootloader, firmware and ART partition to new Flash.
I use a cheap ch341a programmer with SOIC-8 clip.
- Solder the new Flash.
ART partition can either be saved from OpenWrt or read with ch341 programmer after desoldering flash.
It can then either be added to firmware image before writing the new flash or written with modified OpenWrt later.
OpenWrt with 64MB target is here: https://github.com/timowi/openwrt