mirror of
https://github.com/hsoft/collapseos.git
synced 2024-11-14 15:08:05 +11:00
0a26acfee6
The '2' key on my PS/2 keyoard never worked on Collapse OS, I wasn't sure why. I thought the keyboard was broken, but then I tried another one, still broken. But it's only the '2'! The KC sent is 0x1f. Is it a timing problem with the ATtiny? I have yet to wire my prototype for logic probing. Meanwhile, let's apply a band-aid.
80 lines
2.9 KiB
Plaintext
80 lines
2.9 KiB
Plaintext
# Interfacing a PS/2 keyboard
|
|
|
|
Collapse OS needs a way to input commands and keyboards are one
|
|
of the most straightforward ways to proceed. The PS/2 protocol
|
|
is very widespread and relatively simple.
|
|
|
|
We explain here how to interface a PS/2 keyboard with a RC2014.
|
|
|
|
# Gathering parts
|
|
|
|
* A RC2014 Classic that could install the base recipe
|
|
* A PS/2 keyboard. A USB keyboard + adapter also works, if it's
|
|
not too recent (if it still speaks PS/2).
|
|
* A PS/2 female connector.
|
|
* ATtiny85/45/25 (main MCU for the device)
|
|
* 74xx595 (shift register)
|
|
* 40106 inverter gates
|
|
* Diodes for A*, IORQ, RO.
|
|
* Proto board, RC2014 header pins, wires, IC sockets, etc.
|
|
* AVRA (https://github.com/hsoft/avra). The code for this recipe
|
|
hasn't been translated to Collapse OS' AVR assembler yet.
|
|
|
|
# Building the PS/2 interface
|
|
|
|
Let's start with the PS/2 connector (see img/ps2-conn.png),
|
|
which has two pins.
|
|
|
|
Both are connected to the ATtiny45, CLK being on PB2 to have
|
|
INT0 on it.
|
|
|
|
The DATA line is multi-use. That is, PB1 is connected both to
|
|
the PS/2 data line and to the 595's SER. This saves us a
|
|
precious pin.
|
|
|
|
The ATtiny 45 (img/ps2-t45.png) hooks everything together. CE
|
|
comes from the z80 bus (img/ps2-z80.png).
|
|
|
|
The 595 (img/ps2-595.png) allows us to supply the z80 bus with
|
|
data within its 375ns limits. SRCLR is hooked to the CE line so
|
|
that whenever a byte is read, the 595 is zeroed out as fast as
|
|
possible so that the z80 doesn't read "false doubles".
|
|
|
|
The 595, to have its SRCLR becoming effective, needs a RCLK
|
|
trigger, which doesn't happen immediately. It's the ATtiny45, in
|
|
its PCINT interrupt, that takes care of doing that trigger (as
|
|
fast as possible).
|
|
|
|
Our device is read only, on one port. That makes the "Chip
|
|
Enable" (CE) selection rather simple. In my design, I chose the
|
|
IO port 8, so I inverted A3. I chose a 40106 inverter to do
|
|
that, do as you please for your own design.
|
|
|
|
I wanted to hook CE to a flip flop so that the MCU could relax a
|
|
bit more w.r.t. reacting to its PB4 pin changes, but I didn't
|
|
have NAND gates that are fast enough in stock, so I went with
|
|
this design. But otherwise, I would probably have gone the
|
|
flip-flop way. Seems more solid.
|
|
|
|
Then, all you need to do is to assemble code/ps2ctl.asm and load
|
|
it onto your ATtiny.
|
|
|
|
# Using the PS/2 interface
|
|
|
|
To use this interface, you have to build a new Collapse OS
|
|
binary. This binary needs two things.
|
|
|
|
First, we need a "(ps2kc)" routine (see doc/protocol.txt). In
|
|
this case, it's easy, it's ": (ps2kc) 8 PC@ ;". Then, we can
|
|
load PS/2 subsystem. You add "411 414 LOADR". Then, at
|
|
initialization, you add "PS2$". You also need to define PS2_MEM
|
|
at the top. You can probably use "SYSVARS + 0x7a".
|
|
|
|
The PS/2 subsystem provides "(key)" from "(ps2kc)".
|
|
|
|
For debugging purposes, you might not want to go straight to
|
|
plugging PS/2 "(key)" into the system. What I did myself was to
|
|
load the PS/2 subsystem *before* ACIA (which overrides with its
|
|
own "(key)") and added a dummy word in between to access PS/2's
|
|
key.
|