TI-84 Plus CE / 83 PCE Hook Template

This repository serves as a template for creating simple hooks for the TI-84 Plus CE and TI-83 Premium CE calculators (along with their variants). While the best method for creating hooks is to use an app, this is more complicated and less feasible. A good alternative is to create an AppVar with the hook code which resides in the calculator's archive, meaning the hook is more stable than if it was stored in the RAM. However, hooks using this method will be destroyed and require reinstalling after a garbage collect.

About this template

The template provides an installer part (main.asm) and a file for the hook's code (hook.asm). The installer will check if its specific hook is installed, and if it is not, removes any possible conflicting hooks and then creates an archived AppVar with the code in hook.asm. It then sets the hook pointer to the start of the hook's code. If the installer is ran when its specific hook is already installed, it will instead remove it, serving as an uninstaller as well. Once the hook is removed, it will also delete the associated AppVar.

Usage

⚠️ Please read all instructions carefully before using this template. This assumes you already have at least a general familiarity with eZ80 assembly.

To begin using this template, you'll first need to decide which hook type you plan on using. WikiTI has documentation on the various types of hooks here and here. Next, open main.asm and look for the following lines of code which are commented out:

; bit <hook flag>, (iy + <hook flag group>)
...

; ld hl, (<hook pointer location>)
...

; call <clear hook>
...

; jp <set hook>

Replace these lines with the equates associated with the hook you have chosen. For example, a parser hook would look like this:

bit ti.parserHookActive, (iy + ti.hookflags4)
...

ld hl, (ti.parserHookPtr)
...

call ti.ClrParserHook
...

jp ti.SetParserHook

Now that the installer is set up, open hook.asm and place your hook's code in the commented space between the db $83 and ret. The db $83 header is necessary for TI-OS to detect that the code is supposed to be used for a hook.

Once both main.asm and hook.asm are ready, you can build the program using fasmg. If you do not already have fasmg set up on your system, you can follow the guide here.