I've committed the bulk of the Sam Coupe changes. Here's an example how to use the Atom HDD interface:
1. Create suitable CHD. For example, use the "Conner CFA170A" template:
chdman createhd -tp 0 -o samhdd.chd
2. Load MAME with the Atom BIOS, attach Atom interface (and Dallas clock interface) and HDD, boot BDOS 1.5a floppy:
mame64 samcoupe -bios atom -drive2 atom -drive2:atom:ata:0 hdd -flop1 bdos15a.dsk -hard samhdd.chd -exp dallas
We can then load the "formatter" tool:
The HDD is now usable and basically functions the same as 210 floppies (in this case). To make it bootable we can use the "makeboot" tool:
To copy the whole bdos15a disk to HDD we can use "copy record 0 to record 1".
After shutting down MAME we can now run it with just the HDD and it will boot it:
mame64 samcoupe -bios atom -drive2 atom -drive2:atom:ata:0 hdd -hard samhdd.chd -exp dallas
In theory this interface also supports CD-ROMs, and you would be able to copy disk images from CD to the HDD, but once you attach one the HDD/CD detection will hang in an infinite loop. The detection code seems really basic (too basic), so I'm not sure how it works on real hardware.