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 # MCC E-1608 source plugin (sub-project 3 of 4)
 Date: 2026-10-31
 Branch: `feature/source-e1608` (from `feature/source-plugins`, sub-project 1)
 ## Context
 Sub-project 1 added the `DataSource` / `SourceKind` / `SourceRegistry` framework and ported
 UDPS onto it. This sub-project adds a second kind, `e1608`: the Measurement Computing E-1608
 Ethernet DAQ (8 SE / 4 DIFF 16-bit analog inputs, 2 analog outputs, 8 DIO bits, one 32-bit
 counter), with its own connect form and two side-stack panels.
 References for the wire protocol, both written by the user:
 - Primary: `~/Projects/marte2_projects/MCC_E1608_DataSource`, a MARTe2 DataSource
  (`E1608DataSource.{h,cpp}`, `E1608ScanFifo`). Its class comment in the header is the
  authoritative list of parameters and behaviour. It is bound to MARTe2 (`BasicTCPSocket`,
  `StreamString`, `SingleThreadService`), so it is **ported** to plain C++, not linked.
 - Cross-check: `~/Projects/uopi/internal/datasource/mcc/{protocol,e1608}.go`, an independent
  Go implementation of the same protocol.
 No board is available. The mock is the only verification until one is attached.
 ## Decisions
 | Question | Decision |
 | --- | --- |
 | DAC / generator | Static level plus a software waveform (sine, square, triangle, ramp), 10 Hz at most. Runs as a timer inside `poll()`; no extra thread. |
 | Hardware | None available. A protocol mock (`tools/mock_e1608.py`) is the contract. Commands whose layout rests on a single reference (or where the two disagree) are listed as unverified. |
 | Analog input config | Full: per-channel enable and range, global SE/DIFF, MAC discovery, external clock, trigger, DI/counter poll rate. |
 | Digital lines and counter | Plot channels the user chooses, off by default, enabled per line in the connect form. |
 | Acquisition modes | Hardware-paced only (scan rate or external clock). Software-paced mode (`ScanRate = 0`) is not ported. |
 | Structure | Three layers: link, device, source. The bottom two have no GTK or `DataSource` types. |
 ## Design
 ### 1. Files (new, `src/source/e1608/`, plus the mock)
 - `e1608_link.{hpp,cpp}`: UDP discovery (broadcast, or a unicast sweep of a given subnet
  matched by MAC and the E-1608 product id) and connection-code handshake; TCP command
  framing with a timeout; the scan socket on `port + 1`. Plain POSIX sockets.
 - `e1608_device.{hpp,cpp}`: typed commands (AI, AO, DIO read/write/direction, counter
  read/reset, scan queue, scan start/stop, status), the factory calibration read from the board's
  calibration memory, and `decode()`, which turns raw interleaved `uint16` scans into calibrated
  volts (`double`).
 - `e1608_source.{hpp,cpp}`: the `DataSource`: the `poll()` state machine, `Frame` building, the
  DI/counter and generator timers, the atomic readouts for the panels.
 - `e1608_kind.cpp`: the `SourceKind`: the connect form and the two panels.
 - `tools/mock_e1608.py`: the protocol mock.
 - `register_builtin_sources()` registers `e1608` after `udps`.
 ### 2. Data path and threading
 Everything runs inside `poll()` on the producer thread. The GTK thread reaches the board only
 through `post(Command)`.
 `poll(timeout)`:
 1. Drains the posted commands (DAC writes, DIO toggles, counter reset, generator edits).
 2. Runs the connection state machine: optional MAC lookup, handshake, calibration read, DIO
   direction and initial outputs, scan queue and scan start take Disconnected to Scanning. A
   link error fires `on_event(Disconnected)` and retries every 2 s. A connect attempt can block
   `poll()` for up to the command timeout; that delays only the command queue.
 3. Waits on the scan socket for at most the time to the next timer, reads what arrived, keeps a
   partial scan for the next call, decodes the complete scans with the calibration and
   delivers a `Frame`.
 4. Runs the due timers: the DI/counter poll (`DiPollRate`) is a command round trip; the
   generator tick (at most 10 Hz) is a DAC write.
 The frame:
 - Signals: the enabled AI channels (unit `V`, `range_min`/`range_max` from the channel's range),
  the DI lines the user chose (0/1), and the counter if chosen.
 - All signals are scalar; `num_samples` is the number of scans decoded in that read.
 - DI and counter values are held across the block (a step trace).
 - `sampling_rate` is the scan rate on every signal. `counter` is a running frame count.
 - The aggregate rate (enabled channels times scan rate) must stay at or below 250 kS/s. The
  form refuses a configuration above it.
 Overrun: if the board reports a scan overrun the source fires `on_event(Error)` and restarts
 the scan when `AutoRestart` is set; the next frame carries `lost = 1`. This is approximate,
 because the board does not report how many scans it dropped.
 Panel readouts: the source keeps the live DIO inputs, the counter, the DAC levels and the
 generator state in atomics. The panels read them from a GTK timer, so no widget touches the
 source's internals.
 ### 3. Connect form and panels
 Connect form: grouped `AdwExpanderRow`s in the chooser's group. `SourceConfig` stays flat; a
 per-channel setting is a key such as `ai0=BIP10V` (absent means off).
 - Connection: address, MAC, discovery subnet, port, connection code, timeout. `valid()` needs
  an address, or a MAC plus a subnet.
 - Acquisition: scan rate, external clock, trigger mode, auto-restart, calibrate (default on),
  DI/counter poll rate.
 - Analog inputs: global SE or DIFF mode and 8 channel rows (enable, range). In DIFF mode rows
  4 to 7 are insensitive, not hidden. `valid()` also enforces the 250 kS/s aggregate.
 - Digital I/O: direction per bit (I or O), a "plot" switch per input bit, a "plot counter"
  switch, the initial DO value and the initial DAC levels.
 `identity()` is the address, or the MAC when there is no address. A session file is named
 `e1608-<identity>`, port 1, as sub-project 1 defines for non-UDPS kinds. `has_datagrams()` is
 false, so the capture button is disabled.
 Two side-stack panels, both insensitive while disconnected (disabled, not hidden):
 - Analog out: per DAC, a mode (Level, Sine, Square, Triangle, Ramp), a level or amplitude plus
  offset, a frequency of 0.1 to 10 Hz, and an on/off switch. It shows the last voltage written
  and clamps to ±10 V. The generator stops on disconnect and the DACs return to their initial
  levels on reconnect.
 - Digital I/O: eight bit rows; an input bit shows a live LED, an output bit has a toggle that
  posts a write. The counter shows its value and a Reset button. Directions come from the form
  and are not changed at runtime.
 Tab icons are chosen in the plan under the project's bundled-icon rules.
 ### 4. Verification
 Mock (`tools/mock_e1608.py`): UDP discovery with a MAC and the connection-code handshake; TCP
 commands for AI, AO, DIO, the counter, scan queue, scan start/stop, calibration memory and
 status; a scan stream on port+1 at the requested rate with a sine per channel; switches to drop
 the link after N seconds and to report an overrun. Its header lists every command whose layout
 is unverified (single reference, or the references disagree).
 Probe `UDPSCOPE_PROBE_E1608=<delay ms>`, run against the mock with `--source e1608`, extends the
 probe/dump in `src/ui.cpp`. It checks:
 - Frames arrive with the expected channel count and sample rate.
 - The panels are present and insensitive while disconnected.
 - A DAC write, a DIO toggle and a counter reset each reach the mock.
 - A forced link drop leads to a reconnect and a resumed stream.
 - The calibration is applied (the mock serves non-trivial coefficients).
 A decode check needs no mock: a fixed raw buffer decoded against hand-computed volts.
 Baselines are unchanged: the UDPS self-check reads as on `main`, exactly three build warnings,
 no `Gtk-CRITICAL`.
 Errors: a rejected handshake (bad connection code), no device found, timeouts and scan-socket
 loss surface through `on_event(Error)` with a readable message and follow the reconnect cycle.
 A rejected connection code stops the retries: the source stays in Error with that message until the user reconnects.
 Docs: update `architecture.md`, `build-and-run.md`, `verification.md`, `probe-readings.md` and
 `README.md`.
 ## Out of scope
 - Software-paced acquisition (`ScanRate = 0`).
 - A generator faster than 10 Hz, and a dedicated I/O thread.
 - Changing DIO directions at runtime.
 - Per-channel SE/DIFF mixing (one global mode).
 - Verification against a real board.