Support MeterDiv involvement in Watt calculation.

docs/protocol-meter-reading.md

@@ -102,7 +102,7 @@ Blank cells have never been seen to be anything other than zero. Some cells have
   <tr>   <th>12</th> <td colspan=1></td><td colspan=1 align="center">0x01</td><td colspan=2></td></tr>
   <tr>   <th>16</th> <td colspan=1 align="center">0x25</td><td colspan=3 align="center">ExportWh~</td></tr>
   <tr>   <th>20</th> <td colspan=1 align="center">~ExportWh</td><td colspan=2></td><td colspan=1 align="center">0x01</td></tr>
-  <tr>   <th>24</th> <td colspan=1 align="center">0x03</td><td colspan=1></td><td colspan=1 align="center">0x22</td><td colspan=1 align="center">0x01</td></tr>
+  <tr>   <th>24</th> <td colspan=1 align="center">0x03</td><td colspan=1></td><td colspan=1 align="center">0x22</td><td colspan=1 align="center">MeterDiv</td></tr>
   <tr>   <th>28</th> <td colspan=2></td><td colspan=1 align="center">0x02</td><td colspan=1 align="center">0x03</td></tr>
   <tr>   <th>32</th> <td colspan=1></td><td colspan=1 align="center">0x22</td><td colspan=2 align="center">EnergyCostUnit</td></tr>
   <tr>   <th>36</th> <td colspan=1></td><td colspan=1></td><td colspan=1 align="center">0x04</td><td colspan=1></td></tr>
@@ -123,20 +123,26 @@ Bytes 17 to 20, (32 bit int, probably unsigned, LSB)
 
 Cumulative watt-hours sent to the grid. Unknown when the value resets, but probably never resets since ESP32 never sends a clock sync to the MGM111 so it likely just rolls over.
 
-#### PowerVal
+#### MeterDiv
 
-Bytes 41 and 43 (24 bit signed int, LSB)
+Byte 27
 
-The power being sent or consumed at this moment. This is in watts for me but I know in the V2 payload that there is a `MeterDiv`, which means `PowerVal` might be a multiplication of the real wattage. If V7 also has this behavior then `MeterDiv` must have a value of 1 in my readings. So, `MeterDiv` might be byte 2, 13, 23, or 27.
+Used in conjunction with `EnergyCostUnit` and `PowerVal` to calculate the actual wattage.
 
-#### EnergyCostUnit(?)
+#### EnergyCostUnit
 
 Bytes 34 and 35 LSB
 
 Usually `0xE803`, which is `0x03E8` = `1000`. Continuing the V2 theorization that this is the number of watt-hour units per "cost unit".
 Since people are typically charged per kWh, this value is typically 1000.
 
-This value is not currently used in the code.
+#### PowerVal
+
+Bytes 41 and 43 (24 bit signed int, LSB)
+
+The power being sent or consumed at this moment. The actual wattage is calculated with the formula:
+
+`Watts = PowerVal * MeterDiv / (EnergyCostUnit / 1000)`
 
 #### Incrementor
 

esphome/components/emporia_vue_utility/emporia_vue_utility.h

@@ -82,7 +82,9 @@ class EmporiaVueUtility : public PollingComponent, public uart::UARTDevice {
     uint32_t import_wh;  // Payload Bytes 7 to 10
     byte unknown11[6];   // Payload Bytes 11 to 16
     uint32_t export_wh;  // Payload Bytes 17 to 20
-    byte unknown21[13];  // Payload Bytes 21 to 33
+    byte unknown21[6];   // Payload Bytes 21 to 26
+    uint8_t meter_div;   // Payload Byte  27
+    byte unknown28[6];   // Payload Bytes 28 to 33
     uint16_t cost_unit;  // Payload Bytes 34 to 35
     byte unknown36[4];   // Payload Bytes 36 to 39
     uint32_t watts;  // Payload Bytes 40 to 43 : Starts with 0x2A, only use the
@@ -351,13 +353,14 @@ class EmporiaVueUtility : public PollingComponent, public uart::UARTDevice {
       }
 
       cost_unit = mr7->cost_unit;
-      watts = parse_meter_watts_v7(mr7->watts);
+      watts = parse_meter_watts_v7(mr7);
       watt_hours = parse_meter_watt_hours_v7(mr7);
 
       // Extra debugging of non-zero bytes, only on first packet or if
       // debug_ is true
       if ((debug_) || (last_meter_reading == 0)) {
         ESP_LOGD(TAG, "Meter Cost Unit: %d", cost_unit);
+        ESP_LOGD(TAG, "Meter Divisor: %d", mr7->meter_div);
         ESP_LOGD(TAG, "Meter Energy Import Flags: %08x", mr7->import_wh);
         ESP_LOGD(TAG, "Meter Energy Export Flags: %08x", mr7->export_wh);
         ESP_LOGD(TAG, "Meter Power Flags: %08x", mr7->watts);
@@ -620,10 +623,13 @@ class EmporiaVueUtility : public PollingComponent, public uart::UARTDevice {
    *
    * For MGM version 7 and 8
    */
-  float parse_meter_watts_v7(int32_t watts) {
+  float parse_meter_watts_v7(struct MeterReadingV7 *mr) {
     // Read the instant watts value
     // (it's actually a 24-bit int)
-    watts >>= 8;
+    int32_t watts_raw = mr->watts;
+    watts_raw >>= 8;
+    float watts = ((float)watts_raw * (float)mr->meter_div) /
+                  ((float)mr->cost_unit / 1000.0);
 
     if ((watts >= WATTS_MAX) || (watts < WATTS_MIN)) {
       ESP_LOGE(TAG, "Unreasonable watts value %d", watts);