I've started working with the actual BBC BASIC interpreter. As it won't run in its current state on the TI calculator (it relies on a jump table at &FF80..&FFFF to interact with the host, which is protected) I'm using the Z80 emulator I wrote for
Cogwheel to try and puzzle out what the host interface should be doing from the relative sanity of C# code (the jump table is populated with
OUT (n), A instructions which are subsequently trapped and handled by the emulator).

One thing I hadn't realised is that the graphics operations that BBC BASIC offers are actually implemented via the OSWRCH handler (OS WRite CHaracter), which means that BBC BASIC's
PLOT,
MOVE and
DRAW commands will also be available, as well as any commands that use them indirectly (such as
CIRCLE).