Power optimization - Enable HRS3300 (heart rate sensor) sleep mode.

Put the HRS3300 to sleep mode when InfiniTime is going to sleep. This change reduces the power consumption by 130µA when the heart rate sensor is disabled.

Author: JF002

src/drivers/Hrs3300.cpp

@@ -14,6 +14,10 @@
 
 using namespace Pinetime::Drivers;
 
+namespace {
+  static constexpr uint8_t ledDriveCurrentValue = 0x2f;
+}
+
 /** Driver for the HRS3300 heart rate sensor.
  * Original implementation from wasp-os : https://github.com/daniel-thompson/wasp-os/blob/master/wasp/drivers/hrs3300.py
  *
@@ -35,7 +39,7 @@ void Hrs3300::Init() {
   // Note: Setting low nibble to 0x8 per the datasheet results in
   // modulated LED driver output. Setting to 0xF results in clean,
   // steady output during the ADC conversion period.
-  WriteRegister(static_cast<uint8_t>(Registers::PDriver), 0x2f);
+  WriteRegister(static_cast<uint8_t>(Registers::PDriver), ledDriveCurrentValue);
 
   // HRS and ALS both in 15-bit mode results in ~50ms LED drive period
   // and presumably ~50ms ADC conversion period.
@@ -50,13 +54,17 @@ void Hrs3300::Enable() {
   auto value = ReadRegister(static_cast<uint8_t>(Registers::Enable));
   value |= 0x80;
   WriteRegister(static_cast<uint8_t>(Registers::Enable), value);
+
+  WriteRegister(static_cast<uint8_t>(Registers::PDriver), ledDriveCurrentValue);
 }
 
 void Hrs3300::Disable() {
   NRF_LOG_INFO("DISABLE");
   auto value = ReadRegister(static_cast<uint8_t>(Registers::Enable));
   value &= ~0x80;
   WriteRegister(static_cast<uint8_t>(Registers::Enable), value);
+
+  WriteRegister(static_cast<uint8_t>(Registers::PDriver), 0);
 }
 
 uint32_t Hrs3300::ReadHrs() {