Add the terminal's actual input parts to the harness as device models on the
already-modelled SCN2681 at DUART2: a DEC LK401 keyboard (channel A, 4800 8N1)
and a DEC VSXXX-AA mouse (channel B, 4800 8O1), both driven by MAME's host
input and wired bit-by-bit to the DUART (rx_a_w/rx_b_w and a_tx_cb/b_tx_cb).
Route: the docs, not MAME's lk201. MAME's lk201 device executes the 68HC05
firmware 23-001s9-00.bin, which is not in our ROM set (the downloaded zip only
carries the 8051 23-004M2-00.bin, MAME's unused second region), so route 1 is
unusable without sourcing that ROM. The models follow PROTOCOL.md: the keyboard
answers FD with the 4-byte self-test and reports documented keycodes honouring
the division modes; the mouse answers T with its 4-byte self-test and streams
3-byte incremental reports.
One physical-layer detail was required: the SCN2681 receiver mis-samples the
first byte after a receiver reset unless the line is explicitly idle-high
before the start bit. Both models now hold TxD at mark when idle (which is
faithful anyway) -- isolated evidence: bit-banging 0x55 into rx_a_w gives
RHRA=D5 with no idle-high, RHRA=55 with four idle-high bits.
Verified (VT1200_SKIP_LEVEL1=1, input_inject.lua): the OS reads the keyboard
keycode 0xC2 (A) and ~900 bytes of VSXXX reports (dx=+16/+32); after the
self-test it switches the mouse to stream mode; the X11 cursor arrow is visible
at frame 4400 and has moved by frame 4600.
Nothing was tuned for the level-0 I/O data-path test: with no env the boot
still fails it honestly and the regression baseline is unchanged
(PC=3FDCE400 samples=198, 3 PCs). VT1200_IO_PATH_STUB=1 (53/75) and the skip
run (Terminal Manager at frame 3000) are also unchanged. ROM md5 unchanged.
See harness/mame/INPUT_REPORT.md.
