Hello and welcome on Omnimaga
Game frameworks are indeed one of the many things Nspire C/ASM development needs - but it's a lot of work...
For sources of inspiration (or perhaps even C source compatibility ?), have you looked at other GFX libraries (some of which have functions related to a game framework) used on other graphing calculators, such as:
* GenLib (
http://www.yaronet.com/t3 ), run-time dynamic "kernel-based" library for the TI-68k series;
* ExtGraph (
http://tict.ticalc.org,
https://github.com/debrouxl/ExtGraph ), compile-time static library for the TI-68k series;
* the smaller libraries embedded in HPGCC (
http://sourceforge.net/projects/hpgcc/ ), which are, unlike the two ones I've just mentioned, are already targetted at an ARM-based platform ?
One last note for now: you probably want to leave room for two sets of functions, one for the Nspire Clickpad & Touchpad (4-bit grayscale) and one for the Nspire CX & CM (16-bit color). The latter does not currently have native code, but it will eventually become accessible.
And the distinction between those modes should be taken into account early in the design and coding of any framework, because adding it later is harder