feat(RadioInterface): Tx power gain calculation rework (#6796)

- Rename REGULATORY_GAIN_LORA to TX_GAIN_LORA
- Move gain-based Tx power clamping from RadioInterface::applyModemConfig() to RadioInterface::limitPower()
  - User-configured Tx power now matches the Tx power out of the device connector
- Re-order [LoRa Chip]Interface.cpp limitPower() to take place before the final Tx power clamping so we clamp based on the pre-PA Tx power rather than user-configured Tx power

Tested on XIAO BLE variant.

Signed-off-by: Andrew Yong <me@ndoo.sg>
Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

src/configuration.h

@@ -80,10 +80,10 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 // Override user saved region, for producing region-locked builds
 // #define REGULATORY_LORA_REGIONCODE meshtastic_Config_LoRaConfig_RegionCode_SG_923
 
-// Total system gain in dBm to subtract from Tx power to remain within regulatory ERP limit for non-licensed operators
-// This value should be set in variant.h and is PA gain + antenna gain (if system ships with an antenna)
-#ifndef REGULATORY_GAIN_LORA
-#define REGULATORY_GAIN_LORA 0
+// Total system gain in dBm to subtract from Tx power to remain within regulatory and Tx PA limits
+// This value should be set in variant.h and is PA gain + antenna gain (if variant has a non-removable antenna)
+#ifndef TX_GAIN_LORA
+#define TX_GAIN_LORA 0
 #endif
 
 // -----------------------------------------------------------------------------

src/mesh/LR11x0Interface.cpp

@@ -71,6 +71,8 @@ template <typename T> bool LR11x0Interface<T>::init()
 
     RadioLibInterface::init();
 
+    limitPower();
+
     if (power > LR1110_MAX_POWER) // Clamp power to maximum defined level
         power = LR1110_MAX_POWER;
 
@@ -80,8 +82,6 @@ template <typename T> bool LR11x0Interface<T>::init()
         preambleLength = 12; // 12 is the default for operation above 2GHz
     }
 
-    limitPower();
-
 #ifdef LR11X0_RF_SWITCH_SUBGHZ
     pinMode(LR11X0_RF_SWITCH_SUBGHZ, OUTPUT);
     digitalWrite(LR11X0_RF_SWITCH_SUBGHZ, getFreq() < 1e9 ? HIGH : LOW);

src/mesh/RF95Interface.cpp

@@ -122,11 +122,11 @@ bool RF95Interface::init()
     power = dacDbValues.db;
 #endif
 
+    limitPower();
+
     if (power > RF95_MAX_POWER) // This chip has lower power limits than some
         power = RF95_MAX_POWER;
 
-    limitPower();
-
     iface = lora = new RadioLibRF95(&module);
 
 #ifdef RF95_TCXO

src/mesh/RadioInterface.cpp

@@ -528,8 +528,8 @@ void RadioInterface::applyModemConfig()
 
     power = loraConfig.tx_power;
 
-    if ((power == 0) || ((power + REGULATORY_GAIN_LORA > myRegion->powerLimit) && !devicestate.owner.is_licensed))
-        power = myRegion->powerLimit - REGULATORY_GAIN_LORA;
+    if ((power == 0) || ((power > myRegion->powerLimit) && !devicestate.owner.is_licensed))
+        power = myRegion->powerLimit;
 
     if (power == 0)
         power = 17; // Default to this power level if we don't have a valid regional power limit (powerLimit of myRegion defaults
@@ -616,7 +616,12 @@ void RadioInterface::limitPower()
         power = maxPower;
     }
 
-    LOG_INFO("Set radio: final power level=%d", power);
+    if (TX_GAIN_LORA > 0) {
+        LOG_INFO("Requested Tx power: %d dBm; Device LoRa Tx gain: %d dB", power, TX_GAIN_LORA);
+        power -= TX_GAIN_LORA;
+    }
+
+    LOG_INFO("Final Tx power: %d dBm", power);
 }
 
 void RadioInterface::deliverToReceiver(meshtastic_MeshPacket *p)

src/mesh/STM32WLE5JCInterface.cpp

@@ -25,11 +25,11 @@ bool STM32WLE5JCInterface::init()
 
     lora.setRfSwitchTable(rfswitch_pins, rfswitch_table);
 
+    limitPower();
+
     if (power > STM32WLx_MAX_POWER) // This chip has lower power limits than some
         power = STM32WLx_MAX_POWER;
 
-    limitPower();
-
     int res = lora.begin(getFreq(), bw, sf, cr, syncWord, power, preambleLength, tcxoVoltage);
 
     LOG_INFO("STM32WLx init result %d", res);

src/mesh/SX126xInterface.cpp

@@ -69,11 +69,11 @@ template <typename T> bool SX126xInterface<T>::init()
 
     RadioLibInterface::init();
 
+    limitPower();
+
     if (power > SX126X_MAX_POWER) // Clamp power to maximum defined level
         power = SX126X_MAX_POWER;
 
-    limitPower();
-
     int res = lora.begin(getFreq(), bw, sf, cr, syncWord, power, preambleLength, tcxoVoltage, useRegulatorLDO);
     // \todo Display actual typename of the adapter, not just `SX126x`
     LOG_INFO("SX126x init result %d", res);

src/mesh/SX128xInterface.cpp

@@ -62,11 +62,11 @@ template <typename T> bool SX128xInterface<T>::init()
 
     RadioLibInterface::init();
 
+    limitPower();
+
     if (power > SX128X_MAX_POWER) // This chip has lower power limits than some
         power = SX128X_MAX_POWER;
 
-    limitPower();
-
     preambleLength = 12; // 12 is the default for this chip, 32 does not RX at all
 
     int res = lora.begin(getFreq(), bw, sf, cr, syncWord, power, preambleLength);

variants/xiao_ble/variant.h

@@ -145,12 +145,12 @@ static const uint8_t SCK = PIN_SPI_SCK;
 #ifdef EBYTE_E22_900M30S
 // 10dB PA gain and 30dB rated output; based on measurements from
 // https://github.com/S5NC/EBYTE_ESP32-S3/blob/main/E22-900M30S%20power%20output%20testing.txt
-#define REGULATORY_GAIN_LORA 7
+#define TX_GAIN_LORA 7
 #define SX126X_MAX_POWER 22
 #endif
 #ifdef EBYTE_E22_900M33S
 // 25dB PA gain and 33dB rated output; based on TX Power Curve from E22-900M33S_UserManual_EN_v1.0.pdf
-#define REGULATORY_GAIN_LORA 25
+#define TX_GAIN_LORA 25
 #define SX126X_MAX_POWER 8
 #endif
 #endif