From 36ffef083bf3db2d0bfe76f304d88397956c003a Mon Sep 17 00:00:00 2001
From: DAVe3283 <DAVe3283@gmail.com>
Date: Tue, 26 Nov 2019 10:31:33 -0700
Subject: [PATCH] Fix MAX31865 edge case. (#882)

In a heavy EMI environment, reading the current config from the MAX31865 can
fail, such as switching from a 4-wire sensor to a 3-wire sensor. This causes
the temperature value to be off wildly, but still technically valid, so it
doesn't get reported as a sensor failure.

Since we know what configuration we want, rather than send it to the MAX31865
on setup and ask for it over and over (propagating any error as we write it
back), instead store the base configuration and work from that to change modes.
This not only avoids propagating any error, it also saves a lot of unnecessary
reads from the MAX31865.
---
 esphome/components/max31865/max31865.cpp | 26 +++++++++++++++---------
 esphome/components/max31865/max31865.h   |  4 +++-
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/esphome/components/max31865/max31865.cpp b/esphome/components/max31865/max31865.cpp
index 500b5b2883..a3c537a2c2 100644
--- a/esphome/components/max31865/max31865.cpp
+++ b/esphome/components/max31865/max31865.cpp
@@ -37,7 +37,7 @@ void MAX31865Sensor::update() {
   }
 
   // Run fault detection
-  write_register_(CONFIGURATION_REG, 0b11101110, 0b10000110);
+  this->write_config_(0b11101110, 0b10000110);
   const uint32_t start_time = micros();
   uint8_t config;
   uint32_t fault_detect_time;
@@ -55,7 +55,7 @@ void MAX31865Sensor::update() {
   ESP_LOGV(TAG, "Fault detection completed in %uμs.", fault_detect_time);
 
   // Start 1-shot conversion
-  this->write_register_(CONFIGURATION_REG, 0b11100000, 0b10100000);
+  this->write_config_(0b11100000, 0b10100000);
 
   // Datasheet max conversion time is 55ms for 60Hz / 66ms for 50Hz
   auto f = std::bind(&MAX31865Sensor::read_data_, this);
@@ -66,13 +66,15 @@ void MAX31865Sensor::setup() {
   ESP_LOGCONFIG(TAG, "Setting up MAX31865Sensor '%s'...", this->name_.c_str());
   this->spi_setup();
 
-  // Build configuration
-  uint8_t config = 0b00000010;
-  config |= (filter_ & 1) << 0;
+  // Build base configuration
+  base_config_ = 0b00000000;
+  base_config_ |= (filter_ & 1) << 0;
   if (rtd_wires_ == 3) {
-    config |= 1 << 4;
+    base_config_ |= 1 << 4;
   }
-  this->write_register_(CONFIGURATION_REG, 0b11111111, config);
+
+  // Clear any existing faults & set base config
+  this->write_config_(0b00000010, 0b00000010);
 }
 
 void MAX31865Sensor::dump_config() {
@@ -90,7 +92,7 @@ float MAX31865Sensor::get_setup_priority() const { return setup_priority::DATA;
 void MAX31865Sensor::read_data_() {
   // Read temperature, disable V_BIAS (save power)
   const uint16_t rtd_resistance_register = this->read_register_16_(RTD_RESISTANCE_MSB_REG);
-  this->write_register_(CONFIGURATION_REG, 0b11000000, 0b00000000);
+  this->write_config_(0b11000000, 0b00000000);
 
   // Check faults
   const uint8_t faults = this->read_register_(FAULT_STATUS_REG);
@@ -137,12 +139,16 @@ void MAX31865Sensor::read_data_() {
   this->publish_state(temperature);
 }
 
-void MAX31865Sensor::write_register_(uint8_t reg, uint8_t mask, uint8_t bits, uint8_t start_position) {
-  uint8_t value = this->read_register_(reg);
+void MAX31865Sensor::write_config_(uint8_t mask, uint8_t bits, uint8_t start_position) {
+  uint8_t value = base_config_;
 
   value &= (~mask);
   value |= (bits << start_position);
 
+  this->write_register_(CONFIGURATION_REG, value);
+}
+
+void MAX31865Sensor::write_register_(uint8_t reg, uint8_t value) {
   this->enable();
   this->write_byte(reg |= SPI_WRITE_M);
   this->write_byte(value);
diff --git a/esphome/components/max31865/max31865.h b/esphome/components/max31865/max31865.h
index e63be8e6c5..ee2f155f74 100644
--- a/esphome/components/max31865/max31865.h
+++ b/esphome/components/max31865/max31865.h
@@ -43,10 +43,12 @@ class MAX31865Sensor : public sensor::Sensor,
   float rtd_nominal_resistance_;
   MAX31865ConfigFilter filter_;
   uint8_t rtd_wires_;
+  uint8_t base_config_;
   bool has_fault_ = false;
   bool has_warn_ = false;
   void read_data_();
-  void write_register_(uint8_t reg, uint8_t mask, uint8_t bits, uint8_t start_position = 0);
+  void write_config_(uint8_t mask, uint8_t bits, uint8_t start_position = 0);
+  void write_register_(uint8_t reg, uint8_t value);
   const uint8_t read_register_(uint8_t reg);
   const uint16_t read_register_16_(uint8_t reg);
   float calc_temperature_(const float& rtd_ratio);