Merge io_interfaces repo into helpers

README.md

@@ -32,9 +32,9 @@ Debug serial output macros.
 
 Configuration:
 * `#define STA_DEBUG_SERIAL_ENABLE`: Enable module
-* `#define STA_DEBUG_SERIAL_DISABLE`: Forces module off when defined
-* `DEBUG`: Automatically enables module when defined
-* `NDEBUG`: Forces module off when defined
+* `#define STA_DEBUG_SERIAL_FORCE`: Ignore debug defines and always enable output
+* `DEBUG`: Enables output when defined
+* `NDEBUG`: Disables output when defined (overrides DEBUG)
 
 The `sta::DebugSerial` instance must be provided.
 
@@ -78,4 +78,37 @@ Configuration:
 * `#define STA_HAL_DELAY_US_TIM <tim_handle>`: 1 MHz TIM instance used by `sta::delayUs`
 
 TIM time base must be started before using `sta::delayUs` by calling `sta::initHAL`.
-When using the startup system task this is handled automatically.
+When using the startup system task this is handled automatically.
+
+
+## Interfaces
+
+The intention of these interfaces is to provide an abstraction layer for commonly used
+resources. Libraries using these interfaces can be reused on different platforms
+by simply implementing the required interfaces for the selected platform.
+
+Interfaces for the following resources are provided:
+* GPIO pin
+* Mutex
+* Signal
+* SPI
+* UART
+
+
+## HAL implementations
+
+Implementations using the HAL are provided for the following interfaces:
+* GpioPin
+* SpiInterface, SpiDevice
+* UART
+
+To enable these implementations follow the instructions from the individual headers.
+
+
+## Atomic implementations
+
+Implementations using atomic variables are provided for the following interfaces:
+* Mutex
+* Signal
+
+To enable these implementations define `STA_ATOMIC_ENABLE` in `<sta/config.hpp>`.