TI-84+

The TI-84+ is a machine with many advantages, one being that it's very popular. It also has a lot of flash memory and RAM.

Its builtin keyboard and screen, however, are hard to use, especially the screen. With a tiny font, the best we can get is a 24x10 console.

There is, however, a built-in USB controller that might prove very handy.

Recipe

This recipe gets the Collapse OS BASIC shell to run on the TI-84+, using its LCD screen as output and its builtin keyboard as input.

Gathering parts

zasm
A TI-84+ (TI-83+ compatibility is being worked on. See issue #41)
A USB cable
tilp
mktiupgrade
Optional: z80e to emulate

Build the ROM

Running make will result in os.rom being created.

Emulate through z80e

KnightOS has a handy emulator, z80e for TI calculators and it also emulates the screen. It is recommended to use this tool.

Once z80e is installed (build it with SDL support) and os.rom is created, you can run the emulator with:

z80e-sdl -d TI84p --no-rom-check os.rom

You will start with a blank screen, it's normal, you haven't pressed the "ON" key yet. This key is mapped to F12 in the emulator. Once you press it, the Collapse OS prompt will appear.

See z80e's KEYBINDINGS.md file for details.

Upload to the calculator

WARNING: the instructions below will wipe all the contents of your calculator, including TI-OS.

To send your ROM to the calculator, you'll need two more tools: mktiupgrade and tilp.

Once you have them, you need to place your calculator in "bootloader mode", that is, in a mode where it's ready to receive a new binary from its USB cable. To do that you need to:

Shut down the calculator by removing one of the battery.
Hold the DEL key
But the battery back.
A "Waiting... Please install operating system now" message will appear.

Once this is done, you can plug the USB cable in your computer and run make send. This will create an "upgrade file" with mktiupgrade and then push that upgrade file with tilp. tilp will prompt you at some point. Press "1" to continue.

When this is done, you can press the ON button to see Collapse OS' prompt!

Validation errors

Sometimes, when uploading an upgrade file to your calculator, you'll get a validation error. You can always try again, but in my own experience, some specific binaries will simply always be refused by the calculator. Adding random nop or reordering lines (when it makes sense, of course) should fix the problem.

I'm not sure whether it's a bug with the calculator or with mktiupgrade.

Usage

The shell works like a normal BASIC shell, but with very tight screen space.

When pressing a "normal" key, it spits the symbol associated to it depending on the current mode. In normal mode, it spits the digit/symbol. In Alpha mode, it spits the letter. In Alpha+2nd, it spits the uppercase letter.

Special keys are Alpha and 2nd. Pressing them toggles the associated mode. Alpha and 2nd mode don't persist for more than one character. After the character is spit, mode reset to normal.

Pressing 2nd then Alpha will toggle the A-Lock mode, which is a persistent mode. The A-Lock mode makes Alpha enabled all the time. While A-Lock mode is enabled, you have to enable Alpha to spit a digit/symbol.

Simultaneous keypresses have undefined behavior. One of the keys will be registered as pressed. Mode key don't work by simultaneously pressing them with a "normal" key. The presses must be sequential.

Keys that aren't a digit, a letter, a symbol that is part of 7-bit ASCII or one of the two mode key have no effect.

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