feat: add NL-52 USB bulk probe implementation

fix: jinja2 dict hash bug

.gitignore

@@ -1,5 +1,6 @@
 /manuals/
 /data/
+/data-dev/
 /SLM-stress-test/stress_test_logs/
 /SLM-stress-test/tcpdump-runs/
 

SLM-stress-test/NL43_RX55_TCP_Wedge_Investigation_2026-02-18.md

@@ -0,0 +1,403 @@
+# NL-43 + RX55 TCP “Wedge” Investigation (2255 Refusal) — Full Log & Next Steps
+**Last updated:** 2026-02-18  
+**Owner:** Brian / serversdown  
+**Context:** Terra-View / SLMM / field-deployed Rion NL-43 behind Sierra Wireless RX55
+
+---
+
+## 0) What this document is
+This is a **comprehensive, chronological** record of the debugging we did to isolate a failure where the **NL-43’s TCP control port (2255) eventually stops accepting connections** (“wedges”), while other services (notably FTP/21) remain reachable.
+
+This is written to be fed back into future troubleshooting, so it intentionally includes the **full reasoning chain, experiments, commands, packet evidence, and conclusions**.
+
+---
+
+## 1) Architecture (as tested)
+### Network path
+- **Server (SLMM host):** `10.0.0.40`
+- **RX55 WAN IP:** `63.45.161.30`
+- **RX55 LAN subnet:** `192.168.1.0/24`
+- **RX55 LAN gateway:** `192.168.1.1`
+- **NL-43 LAN IP:** `192.168.1.10` (confirmed via ARP OUI + ping; see LAN validation)
+
+### RX55 details
+- **Sierra Wireless RX55**
+- **OS:** 5.2
+- **Firmware:** `01.14.24.00`
+- **Carrier:** Verizon LTE (Band 66)
+
+### Port forwarding rules (RX55)
+- **WAN:2255 → NL-43:2255**  (NL-43 TCP control)
+- **WAN:21   → NL-43:21**    (NL-43 FTP control)
+
+You also experimented with additional forwards:
+- **WAN:2253 → NL-43:2255** (test)
+- **WAN:2253 → NL-43:2253** (test)
+- **WAN:4450 → NL-43:4450** (test)
+
+**Important:** Rule “Input zone / interface” was set to **WAN-NAT**, and Source IP left as **Any IPv4**. This is correct for inbound port-forward behavior on Sierra OS 5.x.
+
+---
+
+## 2) Original problem statement (the “wedge”)
+After running for hours, the NL-43 becomes unreachable over TCP control.
+
+### Symptom signature (WAN-side)
+- Client attempts to connect to `63.45.161.30:2255`
+- Instead of timing out, the client gets **connection refused** quickly.
+- Packet-level: SYN from client → **RST,ACK** back (meaning active refusal vs silent drop)
+
+### Critical operational behavior
+- **Power cycling the NL-43 fixes it.**
+- **Power cycling the RX55 does NOT fix it.**
+- FTP sometimes remains available even while TCP control (2255) is dead.
+
+This combination is what forced us to determine whether:
+- The RX55 is rejecting connections, OR
+- The NL-43 is no longer listening on 2255, OR
+- Something about the RX55 path triggers the NL-43’s control listener to die.
+
+---
+
+## 3) Event timeline evidence (SLMM logs)
+A concrete wedge window was observed on **2026-02-18**:
+
+- 10:55:46 AM — Poll success (Start)
+- 11:00:28 AM — Measurement STOPPED (scheduled stop/download cycle succeeded)
+- 11:55:50 AM — Poll success (Stop)
+- 12:55:55 PM — Poll success (Stop)
+- **1:55:58 PM — Poll failed (attempt 1/3): Errno 111 (connection refused)**
+- 2:56:02 PM — Poll failed (attempt 2/3): Errno 111 (connection refused)
+
+Key interpretation:
+- The wedge occurred sometime between **12:55 and 1:55**.
+- The failure type is **refused**, not timeout.
+
+---
+
+## 4) Early hypotheses (before proof)
+We considered two main buckets:
+
+### A) NL-43-side failure (most suspicious)
+- NL-43 TCP control service crashes / exits / unbinds from 2255
+- socket leak / accept backlog exhaustion
+- “single control session allowed” and it gets stuck thinking a session is active
+- mode/service manager bug (service restart fails after other activities)
+- firmware bug in TCP daemon
+
+### B) RX55-side failure (possible trigger / less likely once FTP works)
+- NAT/forwarding table corruption
+- firewall behavior
+- helper/ALG interference
+- MSS/MTU weirdness causing edge-case behavior
+- session churn behavior causing downstream issues
+
+---
+
+## 5) Key experiments and what they proved
+
+### 5.1) LAN-only stability test (No RX55 path)
+**Test:** NL-43 tested directly on LAN (no modem path involved).
+- Ran **24+ hours**
+- Scheduler start/stop cycles worked
+- Stress test: **500 commands @ 1/sec** → no failure
+- Response time trend decreased (not degrading)
+
+**Result:** The NL-43 appears stable in a “pure LAN” environment.
+
+**Interpretation:** The trigger is likely related to the RX55/WAN environment, connection patterns, or service switching patterns—not just simple uptime.
+
+---
+
+### 5.2) Port-forward behavior: timeout vs refused (RX55 behavior characterization)
+You observed:
+
+- **If a WAN port is NOT forwarded (no rule):** connecting to that port **times out** (silent drop)
+- **If a WAN port IS forwarded to NL-43 but nothing listens:** it **actively refuses** (RST)
+
+Concrete example:
+- Port **4450** with no rule → timeout
+- Port **4450 → NL-43:4450** rule created → connection refused
+
+**Interpretation:** This confirms the RX55 is actually forwarding packets to the NL-43 when a rule exists. “Refused” is consistent with the NL-43 (or RX55 relay behavior) responding quickly because the packet reached the target.
+
+Important nuance:
+- A “refused” on forwarded ports does **not** automatically prove the NL-43 is the one generating RST, because NAT hides the inside host and the RX55 could reject on behalf of an unreachable target. We needed a LAN-side proof test to close the loop.
+
+---
+
+### 5.3) UDP test confusion (and resolution)
+You ran:
+
+```bash
+nc -vzu 63.45.161.30 2255
+nc -vz  63.45.161.30 2255
+```
+
+Observed:
+- UDP: “succeeded”
+- TCP: “connection refused”
+
+Resolution:
+- UDP has **no handshake**. netcat prints “succeeded” if it doesn’t immediately receive an ICMP unreachable. It does **not** mean a UDP service exists.
+- TCP refused is meaningful: a RST implies “no listener” or “actively rejected.”
+
+**Net effect:** UDP test did not change the diagnosis.
+
+---
+
+### 5.4) Packet capture proof (WAN-side)
+You captured a Wireshark/tcpdump summary with these key patterns:
+
+#### Port 2255 (TCP control)
+Example:
+- `10.0.0.40 → 63.45.161.30:2255` SYN
+- `63.45.161.30 → 10.0.0.40` **RST, ACK** within ~50ms
+
+This happened repeatedly.
+
+#### Port 2253 (test port)
+Multiple SYN attempts to 2253 showed **retransmissions and no response**, i.e., **silent drop** (consistent with no rule or not forwarded at that moment).
+
+#### Port 21 (FTP)
+Clean 3-way handshake:
+- SYN → SYN/ACK → ACK
+Then:
+- FTP server banner: `220 Connection Ready`
+Then:
+- `530 Not logged in` (because SLMM was sending non-FTP “requests” as an experiment)
+Session closes cleanly.
+
+**Key takeaway from capture:**
+- TCP transport to NL-43 via RX55 is definitely working (port 21 proves it).
+- Port 2255 is being actively refused.
+
+This strongly suggested “2255 listener is gone,” but still didn’t fully prove whether the refusal was generated internally by NL-43 or by RX55 on behalf of NL-43.
+
+---
+
+## 6) The decisive experiment: LAN-side test while wedged (final proof)
+Because the RX55 does not offer SSH, the plan was to test from **inside the LAN behind the RX55**.
+
+### 6.1) Physical LAN tap setup
+Constraint:
+- NL-43 has only one Ethernet port.
+
+Solution:
+- Insert an unmanaged switch:
+  - RX55 LAN → switch
+  - NL-43 → switch
+  - Windows 10 laptop → switch
+
+This creates a shared L2 segment where the laptop can test NL-43 directly.
+
+### 6.2) Windows LAN validation
+On the Windows laptop:
+
+- `ipconfig` showed:
+  - IP: `192.168.1.100`
+  - Gateway: `192.168.1.1` (RX55)
+- Initial `arp -a` only showed RX55, not NL-43.
+
+You then:
+- pinged likely host addresses and discovered NL-43 responds on **192.168.1.10**
+- `arp -a` then showed:
+  - `192.168.1.10 → 00-10-50-14-0a-d8`
+  - OUI `00-10-50` recognized as **Rion** (matches NL-43)
+
+So LAN identities were confirmed:
+- RX55: `192.168.1.1`
+- NL-43: `192.168.1.10`
+
+### 6.3) The LAN port tests (the smoking gun)
+From Windows:
+
+```powershell
+Test-NetConnection -ComputerName 192.168.1.10 -Port 2255
+Test-NetConnection -ComputerName 192.168.1.10 -Port 21
+```
+
+Results (while the unit was “wedged” from the WAN perspective):
+- **2255:** `TcpTestSucceeded : False`
+- **21:**   `TcpTestSucceeded : True`
+
+**Conclusion (PROVEN):**
+- The NL-43 is reachable on the LAN
+- FTP port 21 is alive
+- **The NL-43 is NOT listening on TCP port 2255**
+- Therefore the RX55 is not the root cause of the refusal. The WAN refusal is consistent with the NL-43 having no listener on 2255.
+
+This is now settled.
+
+---
+
+## 7) What we learned (final conclusions)
+### 7.1) RX55 innocence (for this failure mode)
+The RX55 is not “randomly rejecting” or “breaking TCP” in the way originally feared.
+
+It successfully forwards and supports TCP to the NL-43 on port 21, and the LAN-side test proves the 2255 failure exists *even without NAT/WAN involvement*.
+
+### 7.2) NL-43 control listener failure
+The NL-43’s TCP control service (port 2255) stops listening while:
+- the device remains alive
+- the LAN stack remains alive (ping)
+- FTP remains alive (port 21)
+
+This looks like one of:
+- control daemon crash/exit
+- service unbind
+- stuck service state (e.g., “busy” / “session active forever”)
+- resource leak (sockets/file descriptors) specific to the control service
+- firmware service manager bug (start/stop of services fails after certain sequences)
+
+---
+
+## 8) Additional constraint discovered: “Web App mode” conflicts
+You noted an important operational constraint:
+
+> Turning on the web app disables other interfaces like TCP and FTP.
+
+Meaning the NL-43 appears to have mutually exclusive service/mode behavior (or at least serious conflicts). That matters because:
+- If any workflow toggles modes (explicitly or implicitly), it could destabilize the service lifecycle.
+- It reduces the possibility of using “web UI toggle” as an easy remote recovery mechanism **if** it disables the services needed.
+
+We have not yet run a controlled long test to determine whether:
+- mode switching contributes directly to the 2255 listener dying, OR
+- it happens even in a pure TCP-only mode with no switching.
+
+---
+
+## 9) Immediate operational decision (field tomorrow)
+Because the device is needed in the field immediately, you chose:
+- **Old-school manual deployment**
+- **Manual SD card downloads**
+- Avoid reliance on 2255/TCP control and remote workflows for now.
+
+**Important operational note:**
+The 2255 listener dying does not necessarily stop the NL-43 from measuring; it primarily breaks remote control/polling. Manual SD workflow sidesteps the entire remote control dependency.
+
+---
+
+## 10) What’s next (future work — when the unit is back)
+Because long tests can’t be run before tomorrow, the plan is to resume in a few weeks with controlled experiments designed to isolate the trigger and develop an operational mitigation.
+
+### 10.1) Controlled experiment matrix (recommended)
+Run each test for 24–72 hours, or until wedge occurs, and record:
+- number of TCP connects
+- whether connections are persistent
+- whether FTP is used
+- whether any mode toggling is performed
+- time-to-wedge
+
+#### Test A — TCP-only (ideal baseline)
+- TCP control only (2255)
+- **True persistent connection** (open once, keep forever)
+- No FTP
+- No web mode toggling
+
+Outcome interpretation:
+- If stable: connection churn and/or FTP/mode switching is the trigger.
+- If wedges anyway: pure 2255 daemon leak/bug.
+
+#### Test B — TCP with connection churn
+- Same as A but intentionally reconnect on a schedule (current SLMM behavior)
+- No FTP
+
+Outcome:
+- If this wedges but A doesn’t: churn is the trigger.
+
+#### Test C — FTP activity + TCP
+- Introduce scheduled FTP sessions (downloads) while using TCP control
+- Observe whether wedge correlates with FTP use or with post-download periods.
+
+Outcome:
+- If wedge correlates with FTP, suspect internal service lifecycle conflict.
+
+#### Test D — Web mode interaction (only if safe/possible)
+- Evaluate what toggling web mode does to TCP/FTP services.
+- Determine if any remote-safe “soft reset” exists.
+
+---
+
+## 11) Mitigation options (ranked)
+### Option 1 — Make SLMM truly persistent (highest probability of success)
+If the NL-43 wedges due to session churn or leaked socket states, the best mitigation is:
+- Open one TCP socket per device
+- Keep it open indefinitely
+- Use OS keepalive
+- Do **not** rotate connections on timers
+- Reconnect only when the socket actually dies
+
+This reduces:
+- connect/close cycles
+- NAT edge-case exposure
+- resource churn inside NL-43
+
+### Option 2 — Service “soft reset” (if possible without disabling required services)
+If there exists any way to restart the 2255 service without power cycling:
+- LAN TCP toggle (if it doesn’t require web mode)
+- any “restart comms” command (unknown)
+- any maintenance menu sequence
+then SLMM could:
+- detect wedge
+- trigger soft reset
+- recover automatically
+
+Current constraint: web app mode appears to disable other services, so this may not be viable.
+
+### Option 3 — Hardware watchdog power cycle (industrial but reliable)
+If this is a firmware bug with no clean workaround:
+- Add a remotely controlled relay/power switch
+- On wedge detection, power-cycle NL-43 automatically
+- Optionally schedule a nightly power cycle to prevent leak accumulation
+
+This is “field reality” and often the only long-term move with embedded devices.
+
+### Option 4 — Vendor escalation (Rion)
+You now have excellent evidence:
+- LAN-side proof: 2255 dead while 21 alive
+- WAN packet evidence
+- clear isolation of RX55 innocence
+
+This is strong enough to send to Rion support as a firmware defect report.
+
+---
+
+## 12) Repro “wedge bundle” checklist (for future captures)
+When the wedge happens again, capture these before power cycling:
+
+1) From server:
+- `nc -vz 63.45.161.30 2255` (expect refused)
+- `nc -vz 63.45.161.30 21`   (expect success if FTP alive)
+
+2) From LAN side (via switch/laptop):
+- `Test-NetConnection 192.168.1.10 -Port 2255`
+- `Test-NetConnection 192.168.1.10 -Port 21`
+
+3) Optional: packet capture around the refused attempt.
+
+4) Record:
+- last successful poll timestamp
+- last FTP session timestamp
+- any scheduled start/stop/download cycles near wedge time
+- SLMM connection reuse/rotation settings in effect
+
+---
+
+## 13) Final, current-state summary (as of 2026-02-18)
+- The issue is **NOT** the RX55 rejecting inbound connections.
+- The NL-43 is **alive**, reachable on LAN, and FTP works.
+- The NL-43’s **TCP control listener on 2255 stops listening** while the device remains otherwise healthy.
+- The wedge can occur hours after successful operations.
+- The unit is needed in the field immediately, so investigation pauses.
+- Next phase: controlled tests to isolate trigger + implement mitigation (persistent socket or watchdog reset).
+
+---
+
+## 14) Notes / misc observations
+- The Wireshark trace showed repeated FTP sessions were opened and closed cleanly, but SLMM’s “FTP requests” were not valid FTP (causing `530 Not logged in`). That was part of experimentation, not a normal workflow.
+- UDP “success” via netcat is not meaningful because UDP has no handshake; it simply indicates no ICMP unreachable was returned.
+
+---
+
+**End of document.**

SLM-stress-test/nl52_usb_probe.py

@@ -0,0 +1,165 @@
+#!/usr/bin/env python3
+"""
+RION NL-42 / NL-52 USB serial probe — zero dependencies (stdlib termios only).
+
+The NL-52's USB port enumerates as a virtual COM port ("RION USB to RS232C
+Converter"). On Linux that is almost always handled by an in-kernel USB-serial
+driver (ftdi_sio / cp210x / ch341) which creates /dev/ttyUSB*. This script
+opens that port and sends a few harmless REQUEST commands (no settings are
+changed) to confirm two-way communication.
+
+Protocol (NL-42/NL-52 Serial Interface Manual 55779):
+  Request:  "<Command>?"          + CRLF
+  Setting:  "$<Command>,<param>"  + CRLF      (NOT used here — read-only probe)
+  Reply:    result code "R+0000"  + CRLF, then data line(s) for requests.
+
+Before running:
+  1. On the meter: MENU -> I/O -> Communication Interface -> "USB"
+     (set this BEFORE plugging in the cable).
+  2. Connect a generic USB-A -> mini-B cable directly (no hub).
+  3. Find the port:  ls -l /dev/ttyUSB*   (and `dmesg | tail` after plugging in)
+
+Usage:
+  python3 nl52_usb_probe.py                      # defaults to /dev/ttyUSB0
+  python3 nl52_usb_probe.py --port /dev/ttyUSB0 --baud 115200
+  python3 nl52_usb_probe.py --cmd "System Version?" --cmd "Clock?"
+"""
+
+import argparse
+import os
+import select
+import sys
+import termios
+import time
+
+# Safe, read-only probe commands (all are pure requests).
+DEFAULT_COMMANDS = [
+    "System Version?",   # firmware version — proves the link end-to-end
+    "Clock?",            # current date/time
+    "SD Card Free Size?",
+    "DOD?",              # snapshot of currently displayed values
+]
+
+BAUD_CONSTANTS = {
+    9600: termios.B9600,
+    19200: termios.B19200,
+    38400: termios.B38400,
+    57600: termios.B57600,
+    115200: termios.B115200,
+}
+
+
+def open_serial(port: str, baud: int) -> int:
+    """Open a serial port in raw 8N1, no flow control. Returns an fd."""
+    if baud not in BAUD_CONSTANTS:
+        raise ValueError(f"Unsupported baud {baud}; choose from {sorted(BAUD_CONSTANTS)}")
+
+    fd = os.open(port, os.O_RDWR | os.O_NOCTTY | os.O_NONBLOCK)
+
+    attrs = termios.tcgetattr(fd)
+    iflag, oflag, cflag, lflag, ispeed, ospeed, cc = attrs
+
+    # Raw mode
+    iflag = 0
+    oflag = 0
+    lflag = 0
+    # 8 data bits, enable receiver, ignore modem control lines
+    cflag = termios.CS8 | termios.CREAD | termios.CLOCAL
+    # (no PARENB = no parity, no CSTOPB = 1 stop bit, no CRTSCTS = no flow control)
+
+    bconst = BAUD_CONSTANTS[baud]
+    ispeed = bconst
+    ospeed = bconst
+
+    termios.tcsetattr(fd, termios.TCSANOW, [iflag, oflag, cflag, lflag, ispeed, ospeed, cc])
+    termios.tcflush(fd, termios.TCIOFLUSH)
+    return fd
+
+
+def send(fd: int, line: str):
+    os.write(fd, (line + "\r\n").encode("ascii"))
+
+
+def read_reply(fd: int, timeout: float = 3.0) -> bytes:
+    """Read whatever arrives within `timeout` seconds (idle-gap terminated)."""
+    buf = bytearray()
+    deadline = time.time() + timeout
+    while time.time() < deadline:
+        r, _, _ = select.select([fd], [], [], 0.3)
+        if r:
+            try:
+                chunk = os.read(fd, 4096)
+            except BlockingIOError:
+                continue
+            if chunk:
+                buf.extend(chunk)
+                # Once we've seen a CRLF and there's a brief idle, stop early
+                deadline = min(deadline, time.time() + 0.4)
+    return bytes(buf)
+
+
+def main():
+    ap = argparse.ArgumentParser(description="RION NL-42/NL-52 USB serial probe")
+    ap.add_argument("--port", default="/dev/ttyUSB0")
+    ap.add_argument("--baud", type=int, default=115200,
+                    help="USB CDC usually ignores baud, but RS-232C needs a match")
+    ap.add_argument("--cmd", action="append", dest="cmds",
+                    help="Override probe command(s); repeatable")
+    ap.add_argument("--timeout", type=float, default=3.0)
+    args = ap.parse_args()
+
+    commands = args.cmds or DEFAULT_COMMANDS
+
+    if not os.path.exists(args.port):
+        print(f"[!] {args.port} does not exist.")
+        print("    Plug in the meter (Comm Interface = USB) and check: ls -l /dev/ttyUSB*")
+        print("    Also check the kernel saw it:  dmesg | tail -20")
+        return 2
+
+    try:
+        fd = open_serial(args.port, args.baud)
+    except PermissionError:
+        print(f"[!] Permission denied on {args.port}.")
+        print("    Add yourself to the 'dialout' group, or run with sudo:")
+        print(f"      sudo usermod -aG dialout $USER   (then log out/in)")
+        return 2
+    except Exception as e:
+        print(f"[!] Could not open {args.port}: {e}")
+        return 2
+
+    print(f"[*] Opened {args.port} @ {args.baud} 8N1 (raw, no flow control)")
+    print(f"[*] Sending {len(commands)} read-only request command(s)\n")
+
+    ok = 0
+    try:
+        for cmd in commands:
+            send(fd, cmd)
+            reply = read_reply(fd, args.timeout)
+            decoded = reply.decode("ascii", errors="replace").replace("\r", "\\r").replace("\n", "\\n\n")
+            if reply:
+                ok += 1
+                print(f"  > {cmd}")
+                for line in decoded.splitlines():
+                    print(f"      {line}")
+            else:
+                print(f"  > {cmd}")
+                print(f"      (no response within {args.timeout}s)")
+            print()
+            time.sleep(1.0)  # NL-series likes >=1s between commands
+    finally:
+        os.close(fd)
+
+    if ok == 0:
+        print("[!] No responses. Things to check:")
+        print("    - Meter's Communication Interface is set to USB (not RS-232C)")
+        print("    - ECO / Sleep mode is OFF (both disable the comm interface)")
+        print("    - Right port (try other /dev/ttyUSB* or /dev/ttyACM*)")
+        print("    - For RS-232C path, baud must match the meter's setting")
+        return 1
+
+    print(f"[OK] {ok}/{len(commands)} commands answered — two-way comms confirmed.")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())

app/background_poller.py

@@ -38,6 +38,7 @@ class BackgroundPoller:
         self._running = False
         self._logger = logger
         self._last_cleanup = None  # Track last log cleanup time
+        self._last_pool_log = None  # Track last connection pool heartbeat log
 
     async def start(self):
         """Start the background polling task."""
@@ -89,6 +90,24 @@ class BackgroundPoller:
             except Exception as e:
                 self._logger.warning(f"Log cleanup failed: {e}")
 
+            # Log connection pool status every 15 minutes
+            try:
+                now = datetime.utcnow()
+                if self._last_pool_log is None or (now - self._last_pool_log).total_seconds() > 900:
+                    from app.services import _connection_pool
+                    stats = _connection_pool.get_stats()
+                    conns = stats.get("connections", {})
+                    if conns:
+                        for key, c in conns.items():
+                            self._logger.info(
+                                f"[POOL] {key} — age={c['age_seconds']}s idle={c['idle_seconds']}s alive={c['alive']}"
+                            )
+                    else:
+                        self._logger.info("[POOL] No active connections in pool")
+                    self._last_pool_log = now
+            except Exception as e:
+                self._logger.warning(f"Pool status log failed: {e}")
+
             # Calculate dynamic sleep interval
             sleep_time = self._calculate_sleep_interval()
             self._logger.debug(f"Sleeping for {sleep_time} seconds until next poll cycle")

app/main.py

@@ -76,12 +76,12 @@ app.include_router(routers.router)
 
 @app.get("/", response_class=HTMLResponse)
 def index(request: Request):
-    return templates.TemplateResponse("index.html", {"request": request})
+    return templates.TemplateResponse(request, "index.html")
 
 
 @app.get("/roster", response_class=HTMLResponse)
 def roster(request: Request):
-    return templates.TemplateResponse("roster.html", {"request": request})
+    return templates.TemplateResponse(request, "roster.html")
 
 
 @app.get("/health")

app/services.py

@@ -338,14 +338,14 @@ class ConnectionPool:
                 if self._is_alive(conn):
                     self._drain_buffer(conn.reader)
                     conn.last_used_at = time.time()
-                    logger.debug(f"Pool hit for {device_key} (age={time.time() - conn.created_at:.0f}s)")
+                    logger.info(f"Pool hit for {device_key} (age={time.time() - conn.created_at:.0f}s)")
                     return conn.reader, conn.writer, True
                 else:
                     await self._close_connection(conn, reason="stale")
 
         # Open fresh connection
         reader, writer = await self._open_connection(host, port, timeout)
-        logger.debug(f"New connection opened for {device_key}")
+        logger.info(f"New connection opened for {device_key}")
         return reader, writer, False
 
     async def release(self, device_key: str, reader: asyncio.StreamReader, writer: asyncio.StreamWriter, host: str, port: int):
@@ -454,11 +454,11 @@ class ConnectionPool:
         """Check whether a cached connection is still usable."""
         now = time.time()
 
-        # Age / idle checks
+        # Age / idle checks (value of -1 disables the check)
-        if now - conn.last_used_at > self._idle_ttl:
+        if self._idle_ttl >= 0 and now - conn.last_used_at > self._idle_ttl:
             logger.debug(f"Connection {conn.device_key} idle too long ({now - conn.last_used_at:.0f}s > {self._idle_ttl}s)")
             return False
-        if now - conn.created_at > self._max_age:
+        if self._max_age >= 0 and now - conn.created_at > self._max_age:
             logger.debug(f"Connection {conn.device_key} too old ({now - conn.created_at:.0f}s > {self._max_age}s)")
             return False
 

nl52/__init__.py

@@ -0,0 +1,23 @@
+"""
+RION NL-42 / NL-52 serial control layer.
+
+The NL-52 has no Ethernet option (unlike the NL-43's NX-43EX LAN card); it
+speaks the same ASCII command family over RS-232C or USB (virtual COM port).
+This package provides a dependency-free serial client + parser so the meter
+can be driven directly over USB on the bench, and later bridged onto the
+network via the RX55's serial PAD mode (or a ser2net host).
+
+Modules:
+    protocol  — pure command/response parsing (no I/O, unit-testable)
+    client    — termios-based serial transport + NL52Client command methods
+    cli       — command-line tool for bench testing over USB
+"""
+
+from nl52.protocol import (  # noqa: F401
+    DODSnapshot,
+    DRDSample,
+    ResultError,
+    parse_dod,
+    parse_drd,
+    RESULT_CODES,
+)

nl52/cli.py

@@ -0,0 +1,160 @@
+#!/usr/bin/env python3
+"""
+NL-42 / NL-52 bench CLI — talk to the meter over USB (or RS-232C), no deps.
+
+Setup on the meter first:
+    MENU -> I/O -> Communication Interface -> "USB"   (set BEFORE plugging in)
+    Connect a generic USB-A -> mini-B cable directly (no hub).
+    Find the port:  ls -l /dev/ttyUSB*   (and `dmesg | tail` after plugging in)
+
+Examples:
+    python3 -m nl52.cli probe
+    python3 -m nl52.cli --port /dev/ttyUSB0 status
+    python3 -m nl52.cli start
+    python3 -m nl52.cli stop
+    python3 -m nl52.cli monitor --seconds 10      # DRD stream (needs NX-42EX)
+    python3 -m nl52.cli poll --seconds 10         # DOD polling fallback (~1/s)
+    python3 -m nl52.cli raw "System Version?NL"
+
+Run from the slmm/ directory (so the nl52 package is importable), or just run
+this file directly — it adds slmm/ to sys.path automatically.
+"""
+
+import argparse
+import os
+import sys
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from nl52.client import NL52Client  # noqa: E402
+from nl52.protocol import DODSnapshot, DRDSample, ResultError  # noqa: E402
+
+
+def _fmt(v):
+    return "--" if v is None else (f"{v:.1f}" if isinstance(v, float) else str(v))
+
+
+def _print_dod(s: DODSnapshot):
+    print(f"  Lp   = {_fmt(s.lp)} dB     Leq  = {_fmt(s.leq)} dB    LE = {_fmt(s.le)} dB")
+    print(f"  Lmax = {_fmt(s.lmax)} dB     Lmin = {_fmt(s.lmin)} dB")
+    print(f"  Ly   = {_fmt(s.ly)}        sub Lp = {_fmt(s.sub_lp)} dB")
+    print(f"  LN1..5 = {_fmt(s.ln1)} / {_fmt(s.ln2)} / {_fmt(s.ln3)} / {_fmt(s.ln4)} / {_fmt(s.ln5)}")
+    print(f"  overload={_fmt(s.overload)}  underrange={_fmt(s.underrange)}")
+
+
+def cmd_probe(m: NL52Client, args):
+    print("[*] Probing meter (read-only)...")
+    print(f"  System Version : {m.system_version()}")
+    print(f"  Clock          : {m.get_clock()}")
+    print(f"  Measure state  : {m.measure_state()}")
+    try:
+        print(f"  Battery type   : {m.battery_type()}")
+    except Exception as e:
+        print(f"  Battery type   : (n/a: {e})")
+    try:
+        print(f"  SD free (MB?)  : {m.sd_free_size()}")
+    except Exception as e:
+        print(f"  SD free        : (n/a: {e})")
+    print("[OK] Two-way communication confirmed.")
+
+
+def cmd_status(m: NL52Client, args):
+    state = m.measure_state()
+    print(f"[*] Measure state: {state}")
+    print("[*] DOD snapshot:")
+    _print_dod(m.request_dod())
+
+
+def cmd_start(m: NL52Client, args):
+    print(f"[*] Measure,Start -> {m.measure_start()}")
+    print(f"  state now: {m.measure_state()}")
+
+
+def cmd_stop(m: NL52Client, args):
+    print(f"[*] Measure,Stop -> {m.measure_stop()}")
+    print(f"  state now: {m.measure_state()}")
+
+
+def cmd_monitor(m: NL52Client, args):
+    print(f"[*] DRD stream for {args.seconds}s (requires NX-42EX). Ctrl+C to stop.")
+
+    def on_sample(s: DRDSample):
+        print(f"  #{_fmt(s.counter):>4}  Lp={_fmt(s.lp)}  Leq={_fmt(s.leq)}  "
+              f"Lmax={_fmt(s.lmax)}  Lmin={_fmt(s.lmin)}  sub={_fmt(s.sub_lp)}"
+              f"{'  OVERLOAD' if s.overload else ''}{'  UNDER' if s.underrange else ''}")
+
+    try:
+        m.stream_drd(on_sample, duration=args.seconds)
+    except ResultError as e:
+        print(f"[!] DRD not available ({e}). The meter likely lacks the NX-42EX "
+              f"option — use `poll` instead.")
+
+
+def cmd_poll(m: NL52Client, args):
+    import time
+    print(f"[*] Polling DOD ~1/s for {args.seconds}s. Ctrl+C to stop.")
+    end = time.time() + args.seconds
+    while time.time() < end:
+        s = m.request_dod()
+        print(f"  Lp={_fmt(s.lp)}  Leq={_fmt(s.leq)}  Lmax={_fmt(s.lmax)}  "
+              f"Lmin={_fmt(s.lmin)}  sub={_fmt(s.sub_lp)}"
+              f"{'  OVERLOAD' if s.overload else ''}{'  UNDER' if s.underrange else ''}")
+
+
+def cmd_raw(m: NL52Client, args):
+    resp = m.send(args.command)
+    print(f"  > {args.command}")
+    print(f"  < {resp}")
+
+
+def main():
+    ap = argparse.ArgumentParser(description="RION NL-42/NL-52 bench CLI")
+    ap.add_argument("--port", default="/dev/ttyUSB0")
+    ap.add_argument("--baud", type=int, default=115200)
+    ap.add_argument("--timeout", type=float, default=3.0)
+    ap.add_argument("--echo-on", action="store_true",
+                    help="Don't send Echo,Off on connect")
+
+    sub = ap.add_subparsers(dest="cmd", required=True)
+    sub.add_parser("probe", help="read-only sanity check")
+    sub.add_parser("status", help="measure state + DOD snapshot")
+    sub.add_parser("start", help="Measure,Start")
+    sub.add_parser("stop", help="Measure,Stop")
+    mon = sub.add_parser("monitor", help="DRD stream (needs NX-42EX)")
+    mon.add_argument("--seconds", type=float, default=10)
+    pol = sub.add_parser("poll", help="DOD polling fallback (~1/s)")
+    pol.add_argument("--seconds", type=float, default=10)
+    raw = sub.add_parser("raw", help="send an arbitrary command")
+    raw.add_argument("command")
+
+    args = ap.parse_args()
+
+    if not os.path.exists(args.port):
+        print(f"[!] {args.port} not found. Plug in the meter (Comm Interface=USB) and check:")
+        print("    ls -l /dev/ttyUSB*   ;   dmesg | tail -20")
+        return 2
+
+    handlers = {
+        "probe": cmd_probe, "status": cmd_status, "start": cmd_start,
+        "stop": cmd_stop, "monitor": cmd_monitor, "poll": cmd_poll, "raw": cmd_raw,
+    }
+
+    try:
+        with NL52Client(args.port, baud=args.baud, timeout=args.timeout,
+                        disable_echo=not args.echo_on) as m:
+            handlers[args.cmd](m, args)
+    except PermissionError:
+        print(f"[!] Permission denied on {args.port}. Add yourself to dialout:")
+        print("    sudo usermod -aG dialout $USER   (then log out/in)")
+        return 2
+    except KeyboardInterrupt:
+        print("\n[*] Interrupted.")
+    except (TimeoutError, ResultError) as e:
+        print(f"[!] {type(e).__name__}: {e}")
+        print("    Check: Comm Interface=USB, ECO/Sleep OFF, correct port/baud.")
+        return 1
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())

nl52/client.py

@@ -0,0 +1,288 @@
+"""
+NL-42 / NL-52 serial client — dependency-free (stdlib termios).
+
+Opens the meter's virtual COM port (USB) or RS-232C port and exchanges
+ASCII commands. No pyserial required, so it runs on the dev server with
+nothing to install.
+
+Usage:
+    from nl52.client import NL52Client
+    with NL52Client("/dev/ttyUSB0") as m:
+        print(m.system_version())
+        print(m.measure_state())
+        snap = m.request_dod()
+        print(snap.lp, snap.leq)
+
+Integration note: this client is synchronous for a robust bench tool. The
+parsing in nl52.protocol is I/O-free and reused as-is when this is later
+wrapped for SLMM (async transport, or a serial->TCP bridge behind the
+existing NL43-style TCP client).
+"""
+
+import os
+import select
+import termios
+import time
+from typing import Callable, List, Optional
+
+from nl52.protocol import (
+    CRLF,
+    SUB,
+    DODSnapshot,
+    DRDSample,
+    ResultError,
+    is_result_code,
+    parse_dod,
+    parse_drd,
+)
+
+_BAUD = {
+    9600: termios.B9600,
+    19200: termios.B19200,
+    38400: termios.B38400,
+    57600: termios.B57600,
+    115200: termios.B115200,
+}
+
+# Inter-command spacing (Serial Interface Manual "Rated Values"):
+#   - wait >=200 ms after a reply before the next command
+#   - wait >=1 s between DOD? requests
+MIN_GAP_DEFAULT = 0.2
+MIN_GAP_DOD = 1.0
+
+
+class SerialPort:
+    """Minimal raw 8N1 serial port over a tty fd (no flow control)."""
+
+    def __init__(self, device: str, baud: int = 115200):
+        if baud not in _BAUD:
+            raise ValueError(f"Unsupported baud {baud}; choose {sorted(_BAUD)}")
+        self.device = device
+        self.baud = baud
+        self.fd: Optional[int] = None
+        self._buf = bytearray()  # holds bytes read past the last returned line
+
+    def open(self):
+        fd = os.open(self.device, os.O_RDWR | os.O_NOCTTY | os.O_NONBLOCK)
+        iflag, oflag, cflag, lflag, ispeed, ospeed, cc = termios.tcgetattr(fd)
+        iflag = 0
+        oflag = 0
+        lflag = 0
+        cflag = termios.CS8 | termios.CREAD | termios.CLOCAL
+        ispeed = ospeed = _BAUD[self.baud]
+        termios.tcsetattr(fd, termios.TCSANOW,
+                          [iflag, oflag, cflag, lflag, ispeed, ospeed, cc])
+        termios.tcflush(fd, termios.TCIOFLUSH)
+        self.fd = fd
+
+    def close(self):
+        if self.fd is not None:
+            try:
+                os.close(self.fd)
+            finally:
+                self.fd = None
+
+    def flush_input(self):
+        self._buf.clear()
+        if self.fd is not None:
+            termios.tcflush(self.fd, termios.TCIFLUSH)
+
+    def write(self, data: bytes):
+        assert self.fd is not None
+        os.write(self.fd, data)
+
+    def read_line(self, timeout: float) -> Optional[str]:
+        """Read one CRLF/LF-terminated line. Returns the line without the
+        terminator, or None on timeout with no complete line.
+
+        Bytes received past the newline are retained in self._buf so the next
+        call returns the next line — handles multiple lines arriving in a
+        single read (e.g. result code + data line together)."""
+        assert self.fd is not None
+        deadline = time.time() + timeout
+        while True:
+            if b"\n" in self._buf:
+                line, _, rest = self._buf.partition(b"\n")
+                self._buf = bytearray(rest)
+                return line.decode("ascii", errors="replace").strip()
+            remaining = deadline - time.time()
+            if remaining <= 0:
+                break
+            r, _, _ = select.select([self.fd], [], [], remaining)
+            if not r:
+                break
+            try:
+                chunk = os.read(self.fd, 256)
+            except BlockingIOError:
+                continue
+            if chunk:
+                self._buf.extend(chunk)
+        # Timeout: surface any buffered (un-terminated) bytes as a last resort
+        if self._buf:
+            line = bytes(self._buf)
+            self._buf = bytearray()
+            return line.decode("ascii", errors="replace").strip()
+        return None
+
+
+class NL52Client:
+    def __init__(self, device: str = "/dev/ttyUSB0", baud: int = 115200,
+                 timeout: float = 3.0, disable_echo: bool = True):
+        self.port = SerialPort(device, baud)
+        self.timeout = timeout
+        self.disable_echo = disable_echo
+        self._last_cmd_time = 0.0
+
+    # -- lifecycle ----------------------------------------------------------
+
+    def __enter__(self):
+        self.connect()
+        return self
+
+    def __exit__(self, *exc):
+        self.close()
+
+    def connect(self):
+        self.port.open()
+        if self.disable_echo:
+            # Best-effort: turn echo-back off so replies aren't prefixed with
+            # the command. Ignore failures (some firmware defaults to off).
+            try:
+                self.send("$Echo,Off")
+            except Exception:
+                pass
+
+    def close(self):
+        self.port.close()
+
+    # -- core exchange ------------------------------------------------------
+
+    def _rate_limit(self, command: str):
+        gap = MIN_GAP_DOD if command.strip().upper().startswith("DOD") else MIN_GAP_DEFAULT
+        elapsed = time.time() - self._last_cmd_time
+        if elapsed < gap:
+            time.sleep(gap - elapsed)
+
+    def send(self, command: str) -> str:
+        """Send one command and return its response.
+
+        For request commands (containing '?') returns the data line.
+        For setting commands returns the result code (e.g. 'R+0000').
+        Raises ResultError on R+0001..0004, TimeoutError if no reply.
+
+        Note: NL-52 request commands may carry a parameter *after* the '?'
+        (e.g. 'System Version?NL'), so detection is "contains ?", not
+        "ends with ?". Setting commands start with '$' and never contain '?'.
+        """
+        is_request = "?" in command
+        self._rate_limit(command)
+        self.port.flush_input()
+        self.port.write((command + CRLF).encode("ascii"))
+
+        result_code = self._read_result_code(command)
+
+        try:
+            if result_code != "R+0000":
+                raise ResultError(result_code)
+            if is_request:
+                data = self.port.read_line(self.timeout)
+                if data is None:
+                    raise TimeoutError(f"No data line after {command!r}")
+                return data
+            return result_code
+        finally:
+            self._last_cmd_time = time.time()
+
+    def _read_result_code(self, command: str) -> str:
+        """Read lines until a result code, skipping echo / '$' prompt lines."""
+        sent = command.strip().lstrip("$").strip().lower()
+        deadline = time.time() + self.timeout
+        while time.time() < deadline:
+            line = self.port.read_line(max(0.1, deadline - time.time()))
+            if line is None:
+                continue
+            stripped = line.strip()
+            if not stripped:
+                continue
+            if is_result_code(stripped):
+                return stripped
+            # Skip an echoed command or a bare '$' prompt
+            norm = stripped.lstrip("$").strip().lower()
+            if norm == sent or stripped == "$":
+                continue
+            # Unexpected line — keep looking until timeout
+        raise TimeoutError(f"No result code after {command!r}")
+
+    # -- convenience commands ----------------------------------------------
+
+    def system_version(self, option: str = "NL") -> str:
+        return self.send(f"System Version?{option}")
+
+    def get_clock(self) -> str:
+        return self.send("Clock?")
+
+    def set_clock_now(self):
+        t = time.localtime()
+        # Clock,YYYY/MM/DD HH:MM:SS
+        stamp = time.strftime("%Y/%m/%d %H:%M:%S", t)
+        return self.send(f"$Clock,{stamp}")
+
+    def measure_state(self) -> str:
+        """Returns 'Start' or 'Stop'."""
+        return self.send("Measure?")
+
+    def measure_start(self):
+        return self.send("$Measure,Start")
+
+    def measure_stop(self):
+        return self.send("$Measure,Stop")
+
+    def battery_type(self) -> str:
+        return self.send("Battery Type?")
+
+    def sd_free_size(self) -> str:
+        return self.send("SD Card Free Size?")
+
+    def request_dod(self) -> DODSnapshot:
+        return parse_dod(self.send("DOD?"))
+
+    # -- DRD streaming (requires NX-42EX) -----------------------------------
+
+    def stream_drd(self, on_sample: Callable[[DRDSample], None],
+                   duration: Optional[float] = None,
+                   max_samples: Optional[int] = None):
+        """Start DRD continuous output and call on_sample for each line.
+
+        Stops after `duration` seconds or `max_samples`, then sends SUB to
+        halt the stream. Requires the NX-42EX option on the meter.
+        """
+        self._rate_limit("DRD?")
+        self.port.flush_input()
+        self.port.write(("DRD?" + CRLF).encode("ascii"))
+
+        # First line should be the result code
+        rc = self._read_result_code("DRD?")
+        if rc != "R+0000":
+            self._last_cmd_time = time.time()
+            raise ResultError(rc)
+
+        count = 0
+        deadline = time.time() + duration if duration else None
+        try:
+            while True:
+                if deadline and time.time() >= deadline:
+                    break
+                if max_samples and count >= max_samples:
+                    break
+                line = self.port.read_line(timeout=2.0)
+                if line is None:
+                    continue
+                if is_result_code(line):
+                    continue
+                on_sample(parse_drd(line))
+                count += 1
+        finally:
+            self.port.write(SUB)
+            time.sleep(0.3)
+            self.port.flush_input()
+            self._last_cmd_time = time.time()

nl52/protocol.py

@@ -0,0 +1,172 @@
+"""
+NL-42 / NL-52 serial protocol — pure parsing, no I/O.
+
+Reference: RION NL-42/NL-52 Serial Interface Manual (No. 55779).
+
+Command grammar (shared with the NL-43 family):
+    Setting:  "$" + name + "," + param + CRLF      e.g. "$Measure,Start"
+    Request:  name + "?" + CRLF                     e.g. "DOD?"
+    Reply:    result code "R+0000" + CRLF, then for requests a data line.
+    Stop DRD stream: SUB (0x1A).
+
+This module is intentionally I/O-free so it can be unit-tested without a
+device and reused unchanged behind any transport (serial, or a serial->TCP
+bridge).
+"""
+
+from dataclasses import dataclass, field
+from typing import Dict, List, Optional
+
+CR = "\r"
+LF = "\n"
+CRLF = "\r\n"
+SUB = b"\x1a"  # stop DRD streaming
+
+# Result codes (Serial Interface Manual, "Result code")
+RESULT_CODES: Dict[str, str] = {
+    "R+0000": "Normal end",
+    "R+0001": "Command error (command not recognized)",
+    "R+0002": "Parameter error (bad count/type of parameters)",
+    "R+0003": "Designation error (setting sent to request-only cmd, or vice versa)",
+    "R+0004": "Status error (command not valid in current state)",
+}
+
+# DOD? response field order (d1..d14). Main channel unless noted.
+DOD_FIELDS: List[str] = [
+    "lp", "leq", "le", "lmax", "lmin",
+    "ly",                       # additional processing value (e.g. LCpeak)
+    "ln1", "ln2", "ln3", "ln4", "ln5",
+    "sub_lp",                   # sub channel Lp
+    "overload", "underrange",   # 0/1 flags
+]
+
+# DRD? response field order (d0..d8). Requires NX-42EX.
+DRD_FIELDS: List[str] = [
+    "counter",                  # d0: 1..600
+    "lp", "leq", "lmax", "lmin",
+    "ly",
+    "sub_lp",
+    "overload", "underrange",
+]
+
+# Token the meter returns for a disabled/unavailable display channel.
+_NULL_TOKENS = {"--.-", "-.-", "---.-", ""}
+
+
+class ResultError(Exception):
+    """Raised when the meter returns a non-OK result code (R+0001..0004)."""
+
+    def __init__(self, code: str):
+        self.code = code
+        self.meaning = RESULT_CODES.get(code, "Unknown result code")
+        super().__init__(f"{code}: {self.meaning}")
+
+
+def is_result_code(line: str) -> bool:
+    line = line.strip()
+    return line.startswith("R+") and len(line) == 6 and line[2:].isdigit()
+
+
+def parse_level(token: str) -> Optional[float]:
+    """Parse a space-padded level token into a float, or None if disabled.
+
+    The meter pads to 5 chars and returns '--.-' (leading space) for channels
+    whose display is OFF.
+    """
+    t = token.strip()
+    if t in _NULL_TOKENS or set(t) <= set("-. "):
+        return None
+    try:
+        return float(t)
+    except ValueError:
+        return None
+
+
+def _parse_flag(token: str) -> Optional[bool]:
+    t = token.strip()
+    if t == "1":
+        return True
+    if t == "0":
+        return False
+    return None
+
+
+@dataclass
+class DODSnapshot:
+    """Parsed DOD? snapshot (displayed values). Levels are dB or None if the
+    channel's display is OFF. Measurement state is NOT part of DOD — query
+    Measure? separately."""
+
+    lp: Optional[float] = None
+    leq: Optional[float] = None
+    le: Optional[float] = None
+    lmax: Optional[float] = None
+    lmin: Optional[float] = None
+    ly: Optional[float] = None
+    ln1: Optional[float] = None
+    ln2: Optional[float] = None
+    ln3: Optional[float] = None
+    ln4: Optional[float] = None
+    ln5: Optional[float] = None
+    sub_lp: Optional[float] = None
+    overload: Optional[bool] = None
+    underrange: Optional[bool] = None
+    raw: str = ""
+
+
+@dataclass
+class DRDSample:
+    """Parsed DRD? sample (continuous output, ~every 100 ms)."""
+
+    counter: Optional[int] = None
+    lp: Optional[float] = None
+    leq: Optional[float] = None
+    lmax: Optional[float] = None
+    lmin: Optional[float] = None
+    ly: Optional[float] = None
+    sub_lp: Optional[float] = None
+    overload: Optional[bool] = None
+    underrange: Optional[bool] = None
+    raw: str = ""
+
+
+def _split(resp: str) -> List[str]:
+    return [p for p in resp.strip().split(",")]
+
+
+def parse_dod(resp: str) -> DODSnapshot:
+    """Parse a DOD? data line into a DODSnapshot.
+
+    Tolerant of trailing/short field counts — only maps what is present.
+    """
+    parts = _split(resp)
+    snap = DODSnapshot(raw=resp.strip())
+
+    for idx, name in enumerate(DOD_FIELDS):
+        if idx >= len(parts):
+            break
+        if name in ("overload", "underrange"):
+            setattr(snap, name, _parse_flag(parts[idx]))
+        else:
+            setattr(snap, name, parse_level(parts[idx]))
+
+    return snap
+
+
+def parse_drd(resp: str) -> DRDSample:
+    """Parse a single DRD? data line into a DRDSample."""
+    parts = _split(resp)
+    sample = DRDSample(raw=resp.strip())
+
+    for idx, name in enumerate(DRD_FIELDS):
+        if idx >= len(parts):
+            break
+        if name == "counter":
+            t = parts[idx].strip()
+            sample.counter = int(t) if t.isdigit() else None
+        elif name in ("overload", "underrange"):
+            setattr(sample, name, _parse_flag(parts[idx]))
+        else:
+            setattr(sample, name, parse_level(parts[idx]))
+
+    return sample

nl52/usb_bulk_probe.py

@@ -0,0 +1,128 @@
+#!/usr/bin/env python3
+"""
+RION NL-42/NL-52 USB bulk probe — talks to the meter via libusb directly
+(ctypes, no pyusb/pip needed).
+
+The NL-52's USB serial interface (interface 0) is a plain vendor class with
+two bulk endpoints and NO control protocol — not FTDI/CDC, so no kernel
+serial driver applies. We just claim interface 0 and move ASCII over the
+bulk pipe: write command -> EP 0x03 OUT, read reply <- EP 0x84 IN.
+
+Needs write access to the USB device node (root, or a udev rule granting the
+plugdev group). Run:  sudo python3 nl52/usb_bulk_probe.py
+"""
+
+import ctypes as C
+import time
+
+VID, PID = 0x0EA3, 0x000F
+EP_OUT, EP_IN = 0x03, 0x84
+IFACE = 0
+
+LIBUSB_ERROR_TIMEOUT = -7
+
+lib = C.CDLL("libusb-1.0.so.0")
+lib.libusb_init.argtypes = [C.POINTER(C.c_void_p)]
+lib.libusb_open_device_with_vid_pid.argtypes = [C.c_void_p, C.c_uint16, C.c_uint16]
+lib.libusb_open_device_with_vid_pid.restype = C.c_void_p
+lib.libusb_set_auto_detach_kernel_driver.argtypes = [C.c_void_p, C.c_int]
+lib.libusb_claim_interface.argtypes = [C.c_void_p, C.c_int]
+lib.libusb_release_interface.argtypes = [C.c_void_p, C.c_int]
+lib.libusb_set_interface_alt_setting.argtypes = [C.c_void_p, C.c_int, C.c_int]
+lib.libusb_clear_halt.argtypes = [C.c_void_p, C.c_ubyte]
+lib.libusb_close.argtypes = [C.c_void_p]
+lib.libusb_exit.argtypes = [C.c_void_p]
+lib.libusb_bulk_transfer.argtypes = [
+    C.c_void_p, C.c_ubyte, C.POINTER(C.c_ubyte), C.c_int, C.POINTER(C.c_int), C.c_uint
+]
+lib.libusb_strerror.argtypes = [C.c_int]
+lib.libusb_strerror.restype = C.c_char_p
+
+
+def err(code):
+    return lib.libusb_strerror(code).decode(errors="replace")
+
+
+def main():
+    ctx = C.c_void_p()
+    if lib.libusb_init(C.byref(ctx)) != 0:
+        print("[!] libusb_init failed")
+        return 1
+
+    h = lib.libusb_open_device_with_vid_pid(ctx, VID, PID)
+    if not h:
+        print(f"[!] open {VID:04x}:{PID:04x} failed — device present? running as root?")
+        lib.libusb_exit(ctx)
+        return 1
+
+    lib.libusb_set_auto_detach_kernel_driver(h, 1)
+    rc = lib.libusb_claim_interface(h, IFACE)
+    if rc != 0:
+        print(f"[!] claim_interface({IFACE}) failed: {err(rc)}")
+        lib.libusb_close(h); lib.libusb_exit(ctx)
+        return 1
+
+    print(f"[*] Claimed interface {IFACE} on {VID:04x}:{PID:04x} — bulk OUT 0x{EP_OUT:02x}, IN 0x{EP_IN:02x}")
+
+    # Select alt setting 0 explicitly and clear any endpoint halts left over
+    # from prior (wrong-driver) probing.
+    rc = lib.libusb_set_interface_alt_setting(h, IFACE, 0)
+    print(f"[*] set_interface_alt_setting(0): {err(rc) if rc else 'ok'}")
+    for ep in (EP_OUT, EP_IN):
+        rc = lib.libusb_clear_halt(h, ep)
+        print(f"[*] clear_halt(0x{ep:02x}): {err(rc) if rc else 'ok'}")
+    print()
+
+    def bulk_out(data: bytes, timeout=2000):
+        buf = (C.c_ubyte * len(data)).from_buffer_copy(data)
+        actual = C.c_int(0)
+        rc = lib.libusb_bulk_transfer(h, EP_OUT, buf, len(data), C.byref(actual), timeout)
+        return rc, actual.value
+
+    def bulk_in(n=512, timeout=2000):
+        buf = (C.c_ubyte * n)()
+        actual = C.c_int(0)
+        rc = lib.libusb_bulk_transfer(h, EP_IN, buf, n, C.byref(actual), timeout)
+        return rc, bytes(buf[:actual.value])
+
+    def exchange(cmd: str):
+        rc, n = bulk_out((cmd + "\r\n").encode("ascii"))
+        if rc != 0:
+            print(f"  > {cmd!r:24} OUT failed: {err(rc)}")
+            return
+        # Read until idle (collect result code + data lines)
+        chunks = bytearray()
+        end = time.time() + 2.0
+        while time.time() < end:
+            rrc, data = bulk_in(512, 600)
+            if rrc == 0 and data:
+                chunks.extend(data)
+                end = min(end, time.time() + 0.4)  # brief idle window then stop
+            elif rrc == LIBUSB_ERROR_TIMEOUT:
+                if chunks:
+                    break
+            else:
+                if rrc != 0:
+                    break
+        print(f"  > {cmd!r:24} -> {bytes(chunks)!r}")
+
+    # Read-first sanity check: is the IN endpoint alive / does the device send
+    # anything unsolicited?
+    rrc, data = bulk_in(512, 1000)
+    print(f"[*] read-first IN: rc={err(rrc) if rrc else 'ok'} data={data!r}\n")
+
+    try:
+        for cmd in ["System Version?NL", "Measure?", "DOD?", "Battery Type?"]:
+            exchange(cmd)
+            time.sleep(0.3)
+    finally:
+        lib.libusb_release_interface(h, IFACE)
+        lib.libusb_close(h)
+        lib.libusb_exit(ctx)
+
+    print("\n[done]")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

test_nl52_protocol.py

@@ -0,0 +1,134 @@
+#!/usr/bin/env python3
+"""
+Unit tests for nl52.protocol — DOD/DRD parsing. No hardware required.
+
+Run:  python3 test_nl52_protocol.py
+"""
+
+import sys
+
+from nl52.protocol import (
+    parse_dod,
+    parse_drd,
+    parse_level,
+    is_result_code,
+    ResultError,
+    RESULT_CODES,
+)
+
+PASS = 0
+FAIL = 0
+
+
+def check(name, cond, detail=""):
+    global PASS, FAIL
+    if cond:
+        PASS += 1
+        print(f"  ✓ {name}")
+    else:
+        FAIL += 1
+        print(f"  ✗ {name} {('— ' + detail) if detail else ''}")
+
+
+def test_level_tokens():
+    print("\n[1] Level token parsing")
+    check("plain value", parse_level("55.5") == 55.5)
+    check("space-padded value", parse_level("  60.1") == 60.1)
+    check("disabled channel '--.-' -> None", parse_level(" --.-") is None)
+    check("dashes-only -> None", parse_level("---.-") is None)
+    check("empty -> None", parse_level("   ") is None)
+    check("negative value", parse_level("-3.2") == -3.2)
+
+
+def test_result_codes():
+    print("\n[2] Result code recognition")
+    check("R+0000 is a result code", is_result_code("R+0000"))
+    check("R+0004 is a result code", is_result_code(" R+0004 "))
+    check("data line is not a result code", not is_result_code("55.5,54.2"))
+    check("all 5 codes documented", set(RESULT_CODES) == {
+        "R+0000", "R+0001", "R+0002", "R+0003", "R+0004"})
+    err = ResultError("R+0004")
+    check("ResultError carries meaning", "Status error" in err.meaning, err.meaning)
+
+
+def test_dod_full():
+    print("\n[3] DOD? full 14-field parse")
+    # d1..d14: Lp,Leq,LE,Lmax,Lmin,Ly,LN1..5,subLp,overload,underrange
+    resp = "55.5,54.2,60.1,50.3,45.2,12.3,48.1,50.0,52.3,44.1,43.0,40.2,0,0"
+    s = parse_dod(resp)
+    check("lp", s.lp == 55.5, str(s.lp))
+    check("leq", s.leq == 54.2)
+    check("le", s.le == 60.1)
+    check("lmax", s.lmax == 50.3)
+    check("lmin", s.lmin == 45.2)
+    check("ly", s.ly == 12.3)
+    check("ln1", s.ln1 == 48.1)
+    check("ln5", s.ln5 == 43.0)
+    check("sub_lp", s.sub_lp == 40.2)
+    check("overload False", s.overload is False)
+    check("underrange False", s.underrange is False)
+    check("raw preserved", s.raw == resp)
+
+
+def test_dod_disabled_channels():
+    print("\n[4] DOD? with disabled display channels ('--.-')")
+    # When display is OFF, d2..d12 come back as ' --.-'
+    resp = "55.5, --.-, --.-, --.-, --.-, --.-, --.-, --.-, --.-, --.-, --.-, --.-,1,0"
+    s = parse_dod(resp)
+    check("lp still present", s.lp == 55.5)
+    check("leq disabled -> None", s.leq is None)
+    check("sub_lp disabled -> None", s.sub_lp is None)
+    check("overload True", s.overload is True)
+    check("underrange False", s.underrange is False)
+
+
+def test_dod_space_padded():
+    print("\n[5] DOD? space-padded fixed-width fields")
+    resp = "   55.5,   54.2,   60.1,   50.3,   45.2,   12.3,   48.1,   50.0,   52.3,   44.1,   43.0,   40.2, 0, 1"
+    s = parse_dod(resp)
+    check("padded lp", s.lp == 55.5)
+    check("padded sub_lp", s.sub_lp == 40.2)
+    check("padded underrange True", s.underrange is True)
+
+
+def test_drd():
+    print("\n[6] DRD? sample parse (d0..d8)")
+    # d0=counter,d1=Lp,d2=Leq,d3=Lmax,d4=Lmin,d5=Ly,d6=subLp,d7=ovl,d8=under
+    resp = "12,55.5,54.2,60.1,50.3, --.-,40.2,0,1"
+    s = parse_drd(resp)
+    check("counter int", s.counter == 12, str(s.counter))
+    check("lp", s.lp == 55.5)
+    check("leq", s.leq == 54.2)
+    check("lmax", s.lmax == 60.1)
+    check("lmin", s.lmin == 50.3)
+    check("ly disabled -> None", s.ly is None)
+    check("sub_lp", s.sub_lp == 40.2)
+    check("overload False", s.overload is False)
+    check("underrange True", s.underrange is True)
+
+
+def test_short_field_counts():
+    print("\n[7] Tolerance of short/odd field counts")
+    s = parse_dod("55.5,54.2")  # only first two present
+    check("partial DOD: lp", s.lp == 55.5)
+    check("partial DOD: leq", s.leq == 54.2)
+    check("partial DOD: missing -> None", s.lmax is None)
+    d = parse_drd("7")  # only counter
+    check("partial DRD: counter", d.counter == 7)
+    check("partial DRD: missing lp -> None", d.lp is None)
+
+
+def main():
+    test_level_tokens()
+    test_result_codes()
+    test_dod_full()
+    test_dod_disabled_channels()
+    test_dod_space_padded()
+    test_drd()
+    test_short_field_counts()
+    print(f"\n{'='*50}\nResults: {PASS} passed, {FAIL} failed")
+    return FAIL == 0
+
+
+if __name__ == "__main__":
+    sys.exit(0 if main() else 1)