The -listxml names the software lists each machine and slot card
declares and the floppy drives it can instantiate. --devices now writes
one entry per hash/<list>.xml the release ships under the systems of its
placed machines (111 lists, 666 stay with hash/), and files each floppy
sample under the systems whose drives select its form factor
(floppy.cpp:1428-1473, 1759-1767).
Machines a registered platform declares under one of the profile's
systems seed the walk too: bbcb, cdimono1, cdimono2, dragon32, ep64 and
ep128. Unplaced device sets go from 903 to 861.
The -listxml names, for every machine, its parent (romof), the devices of its default configuration (device_ref) and the cards its slots offer (slotoption). A machine takes the system of the first set on its romof chain a written entry lists, and passes it to each device it can instantiate. A device set reached from one system gets system:, from several the new per-entry systems:, from none neither, and keeps serving every system of the profile. The gap report, the core extras and slots read the entry's own systems, so generate_pack --system and the installer pick by them.
A machine that instantiates a device loads the device's ROMs from <shortname>.zip (src/emu/device.cpp:140-152), and a missing required ROM stops that machine (romload.cpp:529-570, 667-671). The BIOS root scan never sees these sets. mame_hash_scraper --devices --listxml reads them from the -listxml of the release mame.yml pins, refuses another release, and cites each set at the ROM_START block holding its ROMs. The BIOS root merge also wrote refs without the upstream prefix and would have rewritten all 171 of them in mame.yml.
Abdessamad Derraz