pca9554 cache reads (#5137)

esphome/components/pca9554/pca9554.cpp

@@ -26,7 +26,7 @@ void PCA9554Component::setup() {
   this->config_mask_ = 0;
   // Invert mask as the part sees a 1 as an input
   this->write_register_(CONFIG_REG, ~this->config_mask_);
-  // All ouputs low
+  // All outputs low
   this->output_mask_ = 0;
   this->write_register_(OUTPUT_REG, this->output_mask_);
   // Read the inputs
@@ -34,6 +34,14 @@ void PCA9554Component::setup() {
   ESP_LOGD(TAG, "Initialization complete. Warning: %d, Error: %d", this->status_has_warning(),
            this->status_has_error());
 }
+
+void PCA9554Component::loop() {
+  // The read_inputs_() method will cache the input values from the chip.
+  this->read_inputs_();
+  // Clear all the previously read flags.
+  this->was_previously_read_ = 0x00;
+}
+
 void PCA9554Component::dump_config() {
   ESP_LOGCONFIG(TAG, "PCA9554:");
   LOG_I2C_DEVICE(this)
@@ -43,7 +51,16 @@ void PCA9554Component::dump_config() {
 }
 
 bool PCA9554Component::digital_read(uint8_t pin) {
-  this->read_inputs_();
+  // Note: We want to try and avoid doing any I2C bus read transactions here
+  // to conserve I2C bus bandwidth. So what we do is check to see if we
+  // have seen a read during the time esphome is running this loop. If we have,
+  // we do an I2C bus transaction to get the latest value. If we haven't
+  // we return a cached value which was read at the time loop() was called.
+  if (this->was_previously_read_ & (1 << pin))
+    this->read_inputs_();  // Force a read of a new value
+  // Indicate we saw a read request for this pin in case a
+  // read happens later in the same loop.
+  this->was_previously_read_ |= (1 << pin);
   return this->input_mask_ & (1 << pin);
 }
 
@@ -98,6 +115,10 @@ bool PCA9554Component::write_register_(uint8_t reg, uint8_t value) {
 
 float PCA9554Component::get_setup_priority() const { return setup_priority::IO; }
 
+// Run our loop() method very early in the loop, so that we cache read values before
+// before other components call our digital_read() method.
+float PCA9554Component::get_loop_priority() const { return 9.0f; }  // Just after WIFI
+
 void PCA9554GPIOPin::setup() { pin_mode(flags_); }
 void PCA9554GPIOPin::pin_mode(gpio::Flags flags) { this->parent_->pin_mode(this->pin_, flags); }
 bool PCA9554GPIOPin::digital_read() { return this->parent_->digital_read(this->pin_) != this->inverted_; }

esphome/components/pca9554/pca9554.h

@@ -13,6 +13,8 @@ class PCA9554Component : public Component, public i2c::I2CDevice {
 
   /// Check i2c availability and setup masks
   void setup() override;
+  /// Poll for input changes periodically
+  void loop() override;
   /// Helper function to read the value of a pin.
   bool digital_read(uint8_t pin);
   /// Helper function to write the value of a pin.
@@ -22,6 +24,8 @@ class PCA9554Component : public Component, public i2c::I2CDevice {
 
   float get_setup_priority() const override;
 
+  float get_loop_priority() const override;
+
   void dump_config() override;
 
  protected:
@@ -35,6 +39,8 @@ class PCA9554Component : public Component, public i2c::I2CDevice {
   uint8_t output_mask_{0x00};
   /// The state of the actual input pin states - 1 means HIGH, 0 means LOW
   uint8_t input_mask_{0x00};
+  /// Flags to check if read previously during this loop
+  uint8_t was_previously_read_ = {0x00};
   /// Storage for last I2C error seen
   esphome::i2c::ErrorCode last_error_;
 };