Pcal95555Handler

16-pin I²C GPIO expander handler with interrupt support and Agile I/O features.

Construction 

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Pcal95555Handler(BaseI2c& i2c, BaseGpio* int_pin = nullptr);

Key Methods

Method Description
EnsureInitialized() Lazy init, delegates to driver
SetPinDirection(pin, dir) Configure individual pin as input/output
ReadPin(pin, level) Read a single pin level
WritePin(pin, level) Write a single pin level
TogglePin(pin) Toggle a pin output
SetMultipleDirections(mask, dir) Batch direction config (16-bit mask)
WritePins(mask, value) Batch write (16-bit mask + value)
GetChipVariant() Detect PCA9555 vs PCAL9555A
HasAgileIO() Check for extended (PCAL) features
SupportsInterrupts() Check interrupt capability
DrainPendingInterrupts() Deferred ISR processing via atomic flag
GetPin(pin) Get a GpioPin wrapper for BaseGpio integration

Chip Variant Detection

The handler auto-detects the chip variant at initialization:

  • PCA9555 — Basic 16-pin GPIO expander
  • PCAL9555A — Extended with Agile I/O, interrupt masking, output drive strength

Interrupt Handling

Interrupt handling uses a deferred ISR pattern:

  1. ISR sets an std::atomic<bool> flag
  2. Application calls DrainPendingInterrupts() from task context
  3. Handler reads the interrupt status register and processes

This avoids I²C communication in ISR context.

Direct Driver Access 

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auto* drv = handler.GetDriver();
// Access any PCAL95555 register-level API directly

Test Coverage

See examples/esp32/main/handler_tests/pcal95555_handler_comprehensive_test.cpp.