Also how did you make the screenshots at http://martin.poupe.org/casio/tsr/menu.png ? I never got able to transfer any add-in to any emulator I've tried...

DJ_O: I think usage is tricky, but easy for average user (programmer in Basic). We need to specify (and agree on) list of functions and interface (how to communicate), which the TSR will support. As a quick draft one can imagine:
variable A - code of routine to call
0 = nothing
1: get TSR version
...
127: load cas program from flash, name in Str1, filename in Str2
128: delete cas file, name in Str1
Then Basic user would do following:
1. set parameters:
"Game"->Str 1:"\\fls0\Game.g1r"->Str 2
2. specify function:
127->A
3. wait for execute (TSR will reset A to signal execution)
While A:WhileEnd
4. check result (?)
If B:Then "ERROR":Stop":IfEnd
5. use the program
Prog "Game"
6. delete it
"Game"->Str 1:128->A
7. wait for execute ...
While A:WhileEnd
8. check result (?)
If B:Then "ERROR":Stop":IfEnd

One can also imagine really asynchronous processing, we may have function, which will periodically check variables X and Y
and display user defined image (figure) here. You may create e.g. Arkanoid game with nice ball without drawing ball at all (OK you need to draw it once and store it to TSR by another command)