mirror of https://github.com/hsoft/collapseos.git
52 lines
1.9 KiB
Markdown
52 lines
1.9 KiB
Markdown
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# Interfacing a PS/2 keyboard
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Serial connection through ACIA is nice, but you are probably plugging a modern
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computer on the other side of that ACIA, right? Let's go a step further away
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from those machines and drive a PS/2 keyboard directly!
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## Goal
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Have a PS/2 keyboard drive the stdio input of the Collapse OS shell instead of
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the ACIA.
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**Status: work in progress**
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## Gathering parts
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* A RC2014 Classic that could install the base recipe
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* A PS/2 keyboard. A USB keyboard + PS/2 adapter should work, but I haven't
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tried it yet.
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* A PS/2 female connector. Not so readily available, at least not on digikey. I
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de-soldered mine from an old motherboard I had laying around.
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* ATtiny85/45/25 (main MCU for the device)
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* 74xx595 (shift register)
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* 40106 inverter gates
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* Diodes for `A*`, `IORQ`, `RO`.
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* Proto board, RC2014 header pins, wires, IC sockets, etc.
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* [AVRA][avra]
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## Building the PS/2 interface
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TODO. I have yet to draw presentable schematics. By reading `ps2ctl.asm`, you
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might be able to guess how things are wired up.
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It's rather straigtforward: the attiny reads serial data from PS/2 and then
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sends it to the 595. The 595 is wired straight to D7:0 with its `OE` wired to
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address selection + `IORQ` + `RO`
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## Using the PS/2 interface
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As of now, the interface is incomplete and can only be queried through the
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shell's `iord`. I've set my device up for addr `8` (that is, I wired `A3`
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through the inverter, the rest through diodes, and hooked this pudding to `OE`).
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When doing `iord 8` in the shell, I get the scan code of the last key I pressed,
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unless the 595 was "busy" with another code. For example, if I press `A`, my
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next `iord 8` will yield `1C` (the "make" code for "A" in the PS/2 protocol).
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Doing a second `iord 8` right after a first will yield `0`, indicating that the
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device properly detect the first reading attempt and properly flushes the value
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from the 595.
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[avra]: https://github.com/hsoft/avra
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