According to these site https://wiki.openwrt.org/toh/thomson/tg585 he is able to run openwrt,but what is best secured procedure to install firmwer?
The page very explicitly states "NOT supported" in the first line - and https://openwrt.org/supported_devices/432_warning remains valid as well, 16 MB RAM are a hard failure (besides there not being any drivers for the ADSL modem).
@nelliot You asked the same question on IRC, recommendations won't be any different here. Better look for other hardware if you want to run OpenWrt.