Fix NHS serial framing for embedded packet markers

NEWS.adoc

@@ -122,6 +122,41 @@ https://github.com/networkupstools/nut/milestone/13
       rate, data bits, parity, stop bits, flow control, per-byte read timeout,
       and transmission pacing. Also improved serial resource handling and
       reconnection behavior. [issue #3510, PR #3543]
+    * Reworked incoming serial framing to use the total packet length declared
+      by byte `[1]`, instead of treating every `0xFF` as a new packet and every
+      `0xFE` as its end. A leading `0xFF` now starts a frame only while the
+      reader is idle; subsequent `0xFF` and `0xFE` values are preserved as
+      payload or checksum data. The frame is completed at its declared length
+      and accepted only when that final byte is `0xFE`. Declared lengths are
+      also bounded by the receive buffer before further bytes are stored.
+      This prevents valid 18-byte and 50-byte HWINFO replies containing an
+      internal `0xFF` from being split into unrecognized fragments, allowing
+      the driver to obtain model, firmware, serial number and battery-pack
+      information instead of repeatedly requesting HWINFO and delaying normal
+      polling. The raw packet captures and protocol analysis which made this
+      correction possible were contributed by GitHub user `freechurros`.
+      [issue #3592]
+    * Applied follow-up hardware-test feedback from `freechurros`: corrected
+      `interpret_pkt_hwinfo()` to validate the HWINFO checksum instead of the
+      DATA checksum, exposed unrecognized packets through `debug_pkt_raw`, and
+      published the documented lower-case `battery.charger.status` values for
+      compatibility with Home Assistant. [issue #3592]
+    * Send the long, short and compatibility hardware-discovery requests from
+      `upsdrv_initinfo()`, checking the serial descriptor before every request.
+      Failed or partial writes now mark data stale and invalidate the port so
+      the normal update cycle reopens it before further communication.
+    * Refresh cached model-specific data from every valid HWINFO packet and
+      restart discovery after a serial reconnection, allowing a replaced UPS
+      to be identified without restarting the driver.
+    * Added the legacy five-byte compatibility initialization request
+      (`FF 05 01 06 FE`) as a third fallback. The driver first makes six
+      extended initialization attempts, then selects randomly among the
+      extended, normal and compatibility requests so older or otherwise
+      compatibility-dependent NHS units can answer with their supported
+      protocol variant.
+    * Consolidated the NHS model-code metadata into an indexed lookup table,
+      preserving the existing model descriptions and nominal VA mappings while
+      making unknown-code handling explicit.
 
  - `nutdrv_qx` driver updates:
     * Added the `richcomm-svc` USB communication subdriver for older

docs/nut.dict

@@ -2238,6 +2238,7 @@ fosshost
 fp
 fprintf
 freebsd
+freechurros
 freedesktop
 freeipmi
 freetype
@@ -3758,6 +3759,7 @@ xAAAA
 xCC
 xD
 xF
+xFE
 xFF
 xXXXX
 xYYYY