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55 lines
2.9 KiB
Markdown
55 lines
2.9 KiB
Markdown
# tlc-apple2
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Some bits and bobs regarding the Tiger Learning Computer.
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The TLC was a "toy" computer that had an Apple IIe at its core.
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There was a UI that would come up by default that was an early,
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proprietary windowing system that was little more than a program launcher.
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The TLC can be booted and you can get into Applesoft BASIC without any problem.
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The problem is that I/O is pretty difficult. No one with one of these
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machines has come forward with the ability to get anything into or out of the
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existing serial port.
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The goal: get the ROM data of the TLC out of the machine. Hard to do without functional I/O.
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### Audio to the rescue
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One thing the TLC _does_ have is sound. And a headphone jack. So we have... output.
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#### A long time ago...
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In the dark ages, when dinosaurs roamed the Earth, there was cassette tape.
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As an analog-digital storage medium. It was slow, crappy, error-prone, and all
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that - but it at least worked.
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Early Apple II specimens came with this audio interface built-in - the original Apple ][,
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all the way through to the last Apple IIe.
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But the audio jacks and attendant ROM code was missing from the IIgs, the IIc, and the IIc+.
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And the TLC.
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#### Steal all teh cassette ROM
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Handily enough, the early ROM code is quite tidy and compact; this is before the days of the crazy
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gymnastics of the IIe and beyond that moved Heaven and Earth to keep the entry points constant
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(because programmers are bad, and used them literally). The angle of attack:
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* Copy out just enough Apple II ROM code to do the moral equivalent of the monitor's save memory to tape command (i.e. `*300.400W`)
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* Change cassette output (`$C020`) to speaker output (`$C030`)
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* Assemble and get a raw hex dump of that code
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* Type that code into the TLC's RAM and run it, dumping all non-banked ROM (`$C100-$FFFF`)
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* Capture the audio on a modern computer
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* Run that audio through CiderPress, which knows how to take tape audio and reconstruct data from it
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* ???
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* Profit
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The source code to do these activities is in the `src` directory, and the resulting ROM from the Tiger Learning computer is in the `rom` directory. A few pictures of the machine and its on-screen interface are in `doc/images`.
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#### ROM contents
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The files [`C100-FFFF.bin`](https://github.com/david-schmidt/tlc-apple2/blob/master/rom/C100-FFFF.bin)
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and [`C100-FFFF.txt`](https://github.com/david-schmidt/tlc-apple2/blob/master/rom/C100-FFFF.txt)
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are binary and monitor dumps respectively of the ROM as seen normally (i.e. with no banking).
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The files [`C800-CFFF.bin`](https://github.com/david-schmidt/tlc-apple2/blob/master/rom/C800-CFFF.bin)
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and [`C800-CFFF.txt`](https://github.com/david-schmidt/tlc-apple2/blob/master/rom/C800-CFFF.txt)
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are the view of ROM in that region after swapping slot 2 in (i.e. `lda $cfff` and `lda $c200` just before dumping).
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