I've received as a gift a japanese travel router, Planex MZK-DP150N. According to the OpenWRT techdata, it is supported since v18.06.1. In the downloads page, I can find both a kernel.bin and a sysupgrade.bin files. As there is no factory.bin file, I assume that I cannot install OpenWRT from the OEM firmware update system.
On the srchack site there are two pages about installing OpenWRT on this router (///EDIT:new users can only put two links on a post/// from 2015 and 2018 respectively). Google Translate "breaks" both on Firefox and Chromium, so I can't read them fully. I understand that, at least at first, @srchack connects through a serial port to install maybe u-boot, the kernel and some basic port of openwrt, then sysupgrades to a patched version of openwrt that is compatible with the router.
Is there anyway to get/create/compile a factory.bin file?
Is using a serial port soldered to the router's board the only way to install OpenWRT nowadays, or there's a chance to use the firmware's update or a tftp for example?