nicla-system: Avoid High-Z mode when powered from VIN.

Author: sebromero

libraries/Nicla_System/src/BQ25120A.cpp

@@ -30,10 +30,21 @@ uint8_t BQ25120A::getLDOControlRegister()
   return readByte(BQ25120A_ADDRESS, BQ25120A_LDO_CTRL);
 }
 
+bool BQ25120A::runsOnBattery(uint8_t address){
+  uint8_t faults = readByteUnprotected(address, BQ25120A_FAULTS);
+  // Read VIN under voltage fault (VIN_UV on Bit 6) from the faults register.
+  bool runsOnBattery = (faults & 0b01000000) != 0;
+  return runsOnBattery;
+}
+
 void BQ25120A::writeByte(uint8_t address, uint8_t subAddress, uint8_t data)
 {
-  setHighImpedanceModeEnabled(false);
   nicla::_i2c_mutex.lock();
+  // Only enter active mode when runnning on battery.
+  // When powered from VIN, driving CD HIGH would disable charging.
+  if(runsOnBattery(address)){
+    setHighImpedanceModeEnabled(false);
+  }
   Wire1.beginTransmission(address);
   Wire1.write(subAddress);
   Wire1.write(data);
@@ -42,19 +53,27 @@ void BQ25120A::writeByte(uint8_t address, uint8_t subAddress, uint8_t data)
   setHighImpedanceModeEnabled(true);
 }
 
-uint8_t BQ25120A::readByte(uint8_t address, uint8_t subAddress)
-{
-  setHighImpedanceModeEnabled(false);
-  nicla::_i2c_mutex.lock();
+uint8_t BQ25120A::readByteUnprotected(uint8_t address, uint8_t subAddress){
   Wire1.beginTransmission(address);
   Wire1.write(subAddress);
   Wire1.endTransmission(false);
   Wire1.requestFrom(address, 1);
   uint32_t timeout = 100;
   uint32_t start_time = millis();
   while(!Wire1.available() && (millis() - start_time) < timeout) {}
-  uint8_t ret = Wire1.read();
-  nicla::_i2c_mutex.unlock();
+  return Wire1.read();
+}
+
+uint8_t BQ25120A::readByte(uint8_t address, uint8_t subAddress)
+{
+  nicla::_i2c_mutex.lock();
+  // Only enter active mode when runnning on battery.
+  // When powered from VIN, driving CD HIGH would disable charging.
+  if(runsOnBattery(address)){
+    setHighImpedanceModeEnabled(false);
+  }
+  uint8_t ret = readByteUnprotected(address, subAddress);
+  nicla::_i2c_mutex.unlock();  
   setHighImpedanceModeEnabled(true);
   return ret;
 }

libraries/Nicla_System/src/BQ25120A.h

@@ -57,6 +57,14 @@ class BQ25120A
    */
   uint8_t getFastChargeControlRegister();
 
+
+  /**
+   * @brief Determines if the board is charged from the battery.
+   * 
+   * @return true If the board is powered from the battery. False, when powered from USB / VIN.
+   */
+  bool runsOnBattery(uint8_t address);
+
   /**
    * @brief Writes a byte to the BQ25120A over I2C.
    * @param address The I2C address of the BQ25120A.
@@ -89,6 +97,15 @@ class BQ25120A
    * @param enabled Defines if the high impedance mode should be enabled or disabled.
    */
   void setHighImpedanceModeEnabled(bool enabled);
+
+  /**
+   * @brief Reads a byte from the BQ25120A over I2C without locking the bus through the mutex.
+   * 
+   * @param address The I2C address of the BQ25120A.
+   * @param subAddress The memory location of the register to read from.
+   * @return uint8_t The data read from the register.
+   */
+  uint8_t readByteUnprotected(uint8_t address, uint8_t subAddress);
 };
 
 #endif