After the 6847 video controller, the rest of the Acorn Atom is trivial to recreate.

Modelling new machines on old ones provide existing software and avoids the chore of writing it. The Acorn Atom BASIC is small enough to compile into FPGA memory, allowing the writing of programs without external ROM. My first Atom BASIC program was to program BASIC an external ROM. This avoided the need for a device programmer.

The Atom can be modified to run BBC BASIC (with hardware limitations) but I did not get round to implementing that. There are VHDL models of complete BBC micros.