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https://github.com/Jartza/PS2toAmiga

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PS/2 keyboard protocol in it's basic level isn't that hard, it is bidirectional synchronous serial port with clock (CLK) and data (DATA) lines, communicating with PS/2 keyboard using microcontroller has been done multiple times already - which is why I chose to use PS2KeyAdvanced library for Arduino to handle that task - I didn't want to re-invent the wheel, and I had already used PS2KeyAdvanced in earlier projects as well. It also has nice support for Caps Lock, Num Lock etc.

The keycodes read from PS/2 keyboard using PS2KeyAdvanced are then translated to the respective Amiga keycode and sent to wire, using Amiga keyboard protocol.

The converter-code also keeps track of user pressing CTRL-Amiga-Amiga simultaneously and implements resetting the Amiga when those keys are pressed.

There are two different layouts, selectable with Scroll Lock (when Scroll Lock LED is on, second layout is in use). In first layout, Windows/Menu-keys are mapped to respective Amiga-keys on both sides of the space bar, Alt-keys are mapped to respective Amiga versions. On second layout, Left CTRL is mapped to CTRL, Right CTRL to ALT, ALT to Right Amiga-key. Also on second layout, F11 and F12 are mapped to Left and Right Amiga-keys.

Mofifying the keyboard mapping should be pretty straight forward, in the table the comment after keycode denotes the respective key on PS/2 keyboard and the Amiga keycode can be checked from this image. Do not remove values from the table, and do not change the order of the items! Only change the HEX Amiga keycode, before the comment.

Code itself is "quick'n'dirty" -style but should be pretty much commented out so you can modify the internals of it to your own needs - if you have any.

Installing

See PS2KeyAdvanced project for install instructions, for some reason the version 1.0.9 failed to install into my pretty recent Arduino install, but version 1.0.8 worked as well.

For ATTiny85 support I used ATTinyCore, again check their respective site for install instructions to your Arduino IDE.

After installing ATTinyCore and PS2KeyAdvanced, load the project into your Arduino IDE and select following settings:

Board: ATtiny24/45/85 (No bootloader)

Chip: ATtiny85

Clock Source: 16 MHz (PLL)

TImer 1 Clock: CPU frequency

LTO: Enabled

millis(): Enabled

Steps to install to ATTiny85:

Use whatever ISP programmer you have. I used cheap USBASP programmer with 10 -> 6 pin adapter cable, having header pins in ISP connector and then pushing the connector into ISP holes (no header soldered) and keeping them tilted in an angle during programming.

Tools -> Burn bootloader (actually only sets fuses, and enables 16MHz PLL clock)

Sketch -> Verify/Compile

Upload using programmer

You should be done now, if not, verify your programmer connections. I also have had issue sometimes programming the new parts, which are set to 1MHz default in factory - you might need to change your Arduino settings to slow down the programmer for Fuse burning.