feat: receive ChargeLimit_pct from VCU on CAN 0x212 (SKUDAK-516)

Pairs with stm32-hal-vcu PR #42. Adds a runtime "vcuchglim" param that
the VCU broadcasts every 200 ms; on receipt, the param's Change()
callback translates 20-100% to the charger's udcspnt (DC voltage
setpoint) using a linear cell-voltage ramp.

Without this, the teslacharger had no path for the user's app-set
charge limit to actually limit charging — udcspnt was effectively
a compile-time setpoint.

What's added
------------

- Param::vcuchglim in include/param_prj.h:
    PARAM_ENTRY(CAT_CHARGER, vcuchglim, "%", 20, 100, 80, 23)
  - Range 20-100 (matches VCU validation)
  - Default 80% if VCU never connects
  - ID 23 (next free per the comment, bumped to 24)
  - Saveable so a flashed charger paired with a silent VCU still
    behaves predictably across reboots

- can->AddRecv(Param::vcuchglim, 0x212, 0, 8, 1) registration in
  ChargerCAN::MapMessages() — libopeninv's CanMap dispatches to the
  Change() callback on each received frame.

- Param::Change(vcuchglim) handler in src/main.cpp:
    cell_target = 3.30 + (4.15 - 3.30) * (pct - 20) / 80
    udcspnt     = cell_target * 96
  Endpoints chosen to be safe across Tesla LDU / VW MEB / Volt2:
    20%  → 3.30 V/cell × 96 = 316.8 V (deep-cycle storage floor)
    80%  → 3.94 V/cell × 96 = 378.0 V (recommended daily ceiling)
    100% → 4.15 V/cell × 96 = 398.4 V (matches existing udclim default)
  Tuneable here as constants if a particular pack needs a tighter range.

- VER bump 1.19.R → 1.20.R. Combined with the pre-existing -S1 suffix
  the OI web UI shows "4=1.20.R-S1", visually distinct from upstream
  and from the previous Skudak build.

Build
-----

text=25288, links clean. The "RWX LOAD segment" linker warning is
pre-existing on this template, unrelated. No new warnings from this
change.

Version string in the binary verified as "4=1.20.R-S1".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

include/param_prj.h

@@ -39,14 +39,14 @@
  */
 
 //Define a version string of your firmware here
-#define VER 1.19.R
+#define VER 1.20.R
 
 /* Entries must be ordered as follows:
    1. Saveable parameters (id != 0)
    2. Temporary parameters (id = 0)
    3. Display values
  */
-//Next param id (increase when adding new parameter!): 23
+//Next param id (increase when adding new parameter!): 24
 //Next value Id: 2051
 /*              category     name         unit       min     max     default id */
 #define PARAM_LIST \
@@ -63,6 +63,7 @@
     PARAM_ENTRY(CAT_CHARGER, enablepol,   POLARITIES,0,      1,      0,      18  ) \
     PARAM_ENTRY(CAT_CHARGER, idckp,       "",        0,      10000,  1,      20  ) \
     PARAM_ENTRY(CAT_CHARGER, idcki,       "",        0,      10000,  10,     21  ) \
+    PARAM_ENTRY(CAT_CHARGER, vcuchglim,   "%",       20,     100,    80,     23  ) \
     VALUE_ENTRY(state,       STATES,  2043 ) \
     VALUE_ENTRY(uptime,      "s",     2048 ) \
     VALUE_ENTRY(lasterr,     errorListString,  2002 ) \

src/chargercan.cpp

@@ -100,6 +100,13 @@ void ChargerCAN::MapMessages(CanMap* can)
    can->AddSend(Param::idc, 0x109, 24, 16, 1);
    can->AddSend(Param::opmode, 0x109, 40, 3, 5); //Set charging and connlock at once
 
+   /***** SKUDAK VCU command RX (0x212) — SKUDAK-516 user ChargeLimit *****/
+   // Byte 0: ChargeLimit_pct (0-100). Bytes 1-7 reserved 0x00.
+   // Param::Change(vcuchglim) translates % to udcspnt setpoint (see src/main.cpp).
+   // VCU broadcasts every 200 ms once teslacharger detected; charger holds last
+   // value if VCU goes silent.
+   can->AddRecv(Param::vcuchglim, 0x212, 0, 8, 1);
+
    /***** SKUDAK VCU telemetry (0x211) — SKUDAK-448 expanded charger telemetry *****/
    // Byte 0:    state (0=Off, 1=WaitStart, 2=Enable, 3=Activate, 4=Run, 5=Stop)
    // Bytes 1-2: udc (V, gain=1)

src/main.cpp

@@ -114,6 +114,27 @@ void Param::Change(Param::PARAM_NUM paramNum)
          spnt = MIN(Param::Get(Param::idcspnt), Param::Get(Param::idclim));
          dcCurController.SetRef(spnt);
          break;
+      case Param::vcuchglim:
+      {
+         // SKUDAK-516: VCU sends user-set ChargeLimit_pct on CAN 0x212. Translate
+         // percentage to udcspnt (DC voltage setpoint) using a linear cell-voltage
+         // ramp. 96-cell pack (Tesla LDU / VW MEB compatible):
+         //   pct=20  → 3.30 V/cell × 96 = 316.8 V (storage / deep-cycle floor)
+         //   pct=80  → 3.94 V/cell × 96 = 378.0 V (recommended daily ceiling)
+         //   pct=100 → 4.15 V/cell × 96 = 398.4 V (matches existing udclim default)
+         // Endpoints chosen to be safe across Tesla/VW/Volt2 chemistries — adjust
+         // here if a particular pack needs a tighter range. The VCU validates 20-100
+         // before transmit so out-of-range values never arrive.
+         int pct = Param::GetInt(Param::vcuchglim);
+         if (pct < 20)  pct = 20;
+         if (pct > 100) pct = 100;
+         const float CELL_LOW_V   = 3.30f;
+         const float CELL_HIGH_V  = 4.15f;
+         const float CELL_COUNT   = 96.0f;
+         float cell_target = CELL_LOW_V + (CELL_HIGH_V - CELL_LOW_V) * (pct - 20) / 80.0f;
+         Param::SetFloat(Param::udcspnt, cell_target * CELL_COUNT);
+         break;
+      }
       default:
          //Handle general parameter changes here. Add paramNum labels for handling specific parameters
          break;