ps2: interpret KC 0x1f as '2'

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.

blk/411

@@ -9,6 +9,8 @@ CREATE PS2_CODES
 ( 00 ) 0 C, 0 C, 0 C, 0 C, 0 C, 0 C, 0 C, 0 C,
 ( 08 ) 0 C, 0 C, 0 C, 0 C, 0 C, 9 C, '`' C, 0 C,
 ( 10 ) 0 C, 0 C, 0 C, 0 C, 0 C, 'q' C, '1' C, 0 C,
-( 18 ) 0 C, 0 C, 'z' C, 's' C, 'a' C, 'w' C, '2' C, 0 C,
+( I don't know why, but the key 2 is sent as 0x1f by 2 of my
+  keyboards. Is it a timing problem on the ATtiny? TODO )
+( 18 ) 0 C, 0 C, 'z' C, 's' C, 'a' C, 'w' C, '2' C, '2' C,
 ( 20 ) 0 C, 'c' C, 'x' C, 'd' C, 'e' C, '4' C, '3' C, 0 C,
 ( 28 ) 0 C, 32 C, 'v' C, 'f' C, 't' C, 'r' C, '5' C, 0 C,

blk/412

@@ -12,5 +12,5 @@
 ( 00 ) 0 C, 0 C, 0 C, 0 C, 0 C, 0 C, 0 C, 0 C,
 ( 08 ) 0 C, 0 C, 0 C, 0 C, 0 C, 9 C, '~' C, 0 C,
 ( 10 ) 0 C, 0 C, 0 C, 0 C, 0 C, 'Q' C, '!' C, 0 C,
-( 18 ) 0 C, 0 C, 'Z' C, 'S' C, 'A' C, 'W' C, '@' C, 0 C,
+( 18 ) 0 C, 0 C, 'Z' C, 'S' C, 'A' C, 'W' C, '@' C, '@' C,
 ( 20 ) 0 C, 'C' C, 'X' C, 'D' C, 'E' C, '$' C, '#' C, 0 C,

doc/hw/ps2.txt

@@ -9,8 +9,8 @@ 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 + PS/2 adapter should work,
-  but I haven't tried it yet.
+* 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)