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119 lines
5.5 KiB
Markdown
119 lines
5.5 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 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 (Windows hint: run `soundrecorder /file path\to\filename.wav` to get a `.wav`, not a `.wma`)
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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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Nonbanked ROM dump is available in binary and in monitor ROM disassembly form:
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* [`C100-FFFF.bin`](https://github.com/david-schmidt/tlc-apple2/blob/master/rom/C100-FFFF.bin) - Raw binary
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* [`C100-FFFF.txt`](https://github.com/david-schmidt/tlc-apple2/blob/master/rom/C100-FFFF.txt) - Monitor disassembly
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Banked ROM exists in slots 2 and 3. The contents have been dumped as follows:
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Slot 2:
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* [`S2-C800-CFFF.bin`](https://github.com/david-schmidt/tlc-apple2/blob/master/rom/S2-C800-CFFF.bin) - Raw binary
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* [`S2-C800-CFFF.txt`](https://github.com/david-schmidt/tlc-apple2/blob/master/rom/S2-C800-CFFF.txt) - Monitor disassembly
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Slot 3:
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* [`S3-C800-CFFF.bin`](https://github.com/david-schmidt/tlc-apple2/blob/master/rom/S3-C800-CFFF.bin) - Raw binary
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* [`S3-C800-CFFF.txt`](https://github.com/david-schmidt/tlc-apple2/blob/master/rom/S3-C800-CFFF.txt) - Monitor disassembly
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## File contents
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The TLC comes with a virtual disk available in slot 6, drive 1 as volume `/LTWIN`. This is the volume that is booted when the machine turns on.
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The contents of it are as follows:
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```
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]catalog
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/LTWIN
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NAME TYPE BLOCKS MODIFIED CREATED ENDFILE SUBTYPE
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BASIC.SYSTEM SYS 21 6-DEC-91 16:48 6-DEC-91 16:48 10240
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PRODOS SYS 35 6-MAY-93 17:10 2-NOV-92 21:09 17128
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STARTUP BAS 1 <NO DATE> <NO DATE> 176
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KERLT101 BIN 50 11-JAN-96 9:18 11-JAN-96 9:18 24764 A=$1400
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BLOCKS FREE: 14 BLOCKS USED: 114 TOTAL BLOCKS: 128
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```
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#### STARTUP
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Bootstrapping the TLC follows the normal Apple II boot sequence and loads up `PRODOS` and then runs the `STARTUP` Applesoft program from `/LTWIN`.
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`STARTUP` looks like this:
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```
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]load startup
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]list
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10 PRINT CHR$ (4);"BLOAD KERLT101"
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20 CALL 5120
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30 A = PEEK (25)
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40 IF A=1THEN GOTO 10
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50 HOME
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60 VTAB 10: HTAB 10: PRINT "To return to Desktop,"
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70 VTAB 11: HTAB 11: PRINT "please type LTWIN"
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80 POKE (49304),0
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90 POKE (49326),1
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100 END
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```
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The command `LTWIN` is a command that Tiger inserted into the ProDOS external command list (clumsily)
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that basically reboots the system so that you end up back at the graphical interface.
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#### KERLT101
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The contents of `KERLT101` has been dumped and the beginnings of a [6502bench SourceGen](https://github.com/fadden/6502bench/releases) project are here:
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* [`KERLT101.bin`](https://github.com/david-schmidt/tlc-apple2/blob/master/file/KERLT101.bin) - Raw binary
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* [`KERLT101.bin.dis65`](https://github.com/david-schmidt/tlc-apple2/blob/master/file/KERLT101.bin.dis65) - SourceGen disassembly project
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* [`KERLT101.bin_cc65.lst`](https://github.com/david-schmidt/tlc-apple2/blob/master/file/KERLT101.bin_cc65.lst) - ca65 assembly output listing
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Entry is at $1400 which immediately jumps over a data area and starts up for real at $171F. There are clearly a lot of softswitches in the $C0xx space
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that the TLC is using. Figuring out what they do should be an interesting challenge.
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