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RIO: document the board init handshake (test-mode + version) for vRIO

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Decoded from L4RIO.CPP/HPP and verified byte-for-byte against a real
v4.2 board tap: CheckRequest 80 -> board must send TestModeChange ENTER
(8C 01 0D), self-test status stream (85 <status> <unit> <ck>), EXIT
(8C 00 0C), then answer VersionRequest 81 with 86 <maj> <min> <ck>.
Full command map 80-8C both directions, ACK/retransmit rules, and the
~1ms/byte 9600-baud pacing requirement. This is the implementation spec
for the user's vRIO (virtual RIO on COM1): its missing 8C packets are
exactly why the game logs 'RIO never came back from check request!'.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Cyd
2026-07-06 13:35:37 -05:00
co-authored by Claude Fable 5
parent 1872799c7a
commit c18c253658
1 changed files with 38 additions and 0 deletions
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emulator/RIO-NOTES.md
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@@ -275,3 +275,41 @@ the entity gets a broken renderable and the sim eventually dereferences it.
manually pointed at the selected arena's `VIDEO/GEO/<ARENA>` subdir). That is
content/mission configuration, separate from the VPX protocol, the renderer,
and the RIO — all of which now work.
## Board init handshake — what a virtual RIO must implement (2026-07-06)
The user's **vRIO** (virtual RIO on COM1) passed analog polling but the game
still printed its init complaint. Root cause decoded from
[L4RIO.CPP:901-975](../CODE/RP/MUNGA_L4/L4RIO.CPP) +
[L4RIO.HPP:138-152](../CODE/RP/MUNGA_L4/L4RIO.HPP) and verified byte-for-byte
against a real-board tap (riotap_arena.txt, fw v4.2):
Command map (packet = cmd + body + 7-bit checksum `sum&0x7F`; FC=ACK FD=NAK
FE=RESTART FF=IDLE): game→board `80` CheckRequest, `81` VersionRequest,
`82` AnalogRequest, `83` ResetRequest, `84` LampRequest; board→game
`85` CheckReply(status,unit; status: 0=BoardOk 1=BoardMissing 2=BoardBad
3=LampBad 4/5/6=Restart/Abandon/FullBuffer counts), `86` VersionReply(maj,min),
`87` AnalogReply(10 data bytes), `88`/`89` Button press/release,
`8A`/`8B` Key press/release, `8C` TestModeChange(1=enter 0=exit).
Init sequence (game side bombs with "RIO never came back from check request /
test mode / version request!" if any step times out at 5s):
1. game pulses DTR (assert 0.1s, drop, wait 1s) = hardware board reset
2. game `80 00` → board `FC`
3. **board `8C 01 0D` (TestModeChange ENTER)** ← the packet vRIO was missing;
game waits ≤5s for it, sets TestModeActive
4. board self-test (~0.6s on the real board), streaming `85 <status> <unit>
<ck>` per subsystem (these are swallowed during test mode, not host events;
the bench board reports status=1 BoardMissing for units 08,10,11,18,19,1A,30)
5. **board `8C 00 0C` (TestModeChange EXIT)** — game waits ≤5s
6. game `81 01` → board `FC`, then **`86 04 02 0C` (VersionReply v4.2)**;
game loops until MajorRevision != 0xFF
7. normal ops: `82 02` analog polls / button+key events. NOTE: the game sends
requests ONLY when `operational && !TestModeActive` — a board that enters
test mode and never exits mutes the game permanently.
Every board packet is retransmitted until the game ACKs `FC` (within the
TXMAXIDLE window; ~33ms with the patched EXE). Byte pacing at the 9600-baud
wire rate (~1ms/byte) matters: vRIO blasting bytes back-to-back caused NAK/
restart churn during init until the user added pacing.