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136 lines
5.3 KiB
Markdown
136 lines
5.3 KiB
Markdown
# TI-84+
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The TI-84+ is a machine with many advantages, one being that it's very popular.
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It also has a lot of flash memory and RAM.
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Its builtin keyboard and screen, however, are hard to use, especially the
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screen. With a tiny font, the best we can get is a 24x10 console.
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There is, however, a built-in USB controller that might prove very handy.
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I haven't opened one up yet, but apparently, they have limited scavenging value
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because its z80 CPU is packaged in a TI-specific chip. Due to its sturdy design,
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and its ample RAM and flash, we could imagine it becoming a valuable piece of
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equipment if found intact.
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The best pre-collapse ressource about it is
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[WikiTI](http://wikiti.brandonw.net/index.php).
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As it is now, with its tiny screen and cumbersome keyboard, Collapse OS is
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not really usable on the TI-84+. One could imagine a scenario where one has a
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terminal and uses the TI-84+ through the link for its large amount of flash and
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RAM. But using it standalone? Nah, not even post-collapse.
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Therefore, this recipe is more of a "look, I run!" demo.
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## Recipe
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This recipe gets the Collapse OS interpreter to run on the TI-84+, using its LCD
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screen as output and its builtin keyboard as input.
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## Gathering parts
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* [zasm][zasm]
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* A TI-84+ (TI-83+ compatibility is being worked on. See issue #41)
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* A USB cable
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* [tilp][tilp]
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* [mktiupgrade][mktiupgrade]
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## Build the ROM
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Running `make` will result in `os.rom` being created.
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## Emulate
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Collapse OS has a builtin TI-84+ emulator using XCB for display in `emul/hw/ti`.
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You can invoke it with `make emul`.
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You will start with a blank screen, it's normal, you haven't pressed the "ON"
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key yet. This key is mapped to tilde (~) in the emulator. Once you press it, the
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Collapse OS prompt will appear. See `emul/hw/ti/README.md` for details.
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## Upload to the calculator
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### Background notes
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Getting software to run on it is a bit tricky because it needs to be signed
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with TI-issued private keys. Those keys have long been found and are included
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in `keys/`. With the help of the
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[mktiupgrade](https://github.com/KnightOS/mktiupgrade), an upgrade file can be
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prepared and then sent through the USB port with the help of
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[tilp](http://lpg.ticalc.org/prj_tilp/).
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That, however, requires a modern computing environment. As of now, there is no
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way of installing Collapse OS on a TI-8X+ calculator from another Collapse OS
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system.
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Because it is not on the roadmap to implement complex cryptography in Collapse
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OS, the plan is to build a series of pre-signed bootloader images. The
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bootloader would then receive data through either the Link jack or the USB port
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and write that to flash (I haven't verified that yet, but I hope that data
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written to flash this way isn't verified cryptographically by the calculator).
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As modern computing fades away, those pre-signed binaries would become opaque,
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but at least, would allow bootstrapping from post-modern computers.
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### Instructions
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**WARNING: the instructions below will wipe all the contents of your calculator,
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including TI-OS.**
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To send your ROM to the calculator, you'll need two more tools:
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[mktiupgrade][mktiupgrade] and [tilp][tilp].
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Once you have them, you need to place your calculator in "bootloader mode",
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that is, in a mode where it's ready to receive a new binary from its USB cable.
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To do that you need to:
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1. Shut down the calculator by removing one of the battery.
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2. Hold the DEL key
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3. But the battery back.
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4. A "Waiting... Please install operating system now" message will appear.
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Once this is done, you can plug the USB cable in your computer and run
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`make send`. This will create an "upgrade file" with `mktiupgrade` and then
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push that upgrade file with `tilp`. `tilp` will prompt you at some point.
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Press "1" to continue.
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When this is done, you can press the ON button to see Collapse OS' prompt!
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## Validation errors
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Sometimes, when uploading an upgrade file to your calculator, you'll get a
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validation error. You can always try again, but in my own experience, some
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specific binaries will simply always be refused by the calculator. Adding
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random `nop` or reordering lines (when it makes sense, of course) should fix
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the problem.
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I'm not sure whether it's a bug with the calculator or with `mktiupgrade`.
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## Usage
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The shell works like a normal BASIC shell, but with very tight screen space.
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When pressing a "normal" key, it spits the symbol associated to it depending
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on the current mode. In normal mode, it spits the digit/symbol. In Alpha mode,
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it spits the letter. In Alpha+2nd, it spits the uppercase letter.
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Special keys are Alpha and 2nd. Pressing them toggles the associated mode.
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Alpha and 2nd mode don't persist for more than one character. After the
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character is spit, mode reset to normal.
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Pressing 2nd then Alpha will toggle the A-Lock mode, which is a persistent mode.
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The A-Lock mode makes Alpha enabled all the time. While A-Lock mode is enabled,
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you have to enable Alpha to spit a digit/symbol.
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Simultaneous keypresses have undefined behavior. One of the keys will be
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registered as pressed. Mode key don't work by simultaneously pressing them with
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a "normal" key. The presses must be sequential.
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Keys that aren't a digit, a letter, a symbol that is part of 7-bit ASCII or one
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of the two mode key have no effect.
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[zasm]: ../../tools/emul
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[mktiupgrade]: https://github.com/KnightOS/mktiupgrade
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[tilp]: http://lpg.ticalc.org/prj_tilp/
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