IO Limits

Overview

CIOLimits is a framework-level utility used by IO objects to enforce runtime constraints on data values. It allows defining a valid range and step for input and output data, which is especially useful for setpoint validation or protecting hardware from out-of-bounds commands.

The validation is applied against three optional descriptor-backed arrays: min, max, and step.

Implementation

The CIOLimits class stores pointers to data in the descriptor and performs validation when its validate() method is called. It supports all standard Dawn data types (integer, fixed-point, and floating-point).

Validation rules: 1. Min/Max: The value must be within the inclusive range [min, max]. 2. Step: If a non-zero step is defined, the value must satisfy (value - min) % step == 0. For floating-point types, this is checked with an appropriate epsilon.

If the CONFIG_DAWN_IO_LIMITS Kconfig option is disabled, the class becomes a no-op to save resources.

Configuration

Limits are typically configured as part of a compatible IO object’s configuration block.

Kconfig

CONFIG_DAWN_IO_LIMITS: Enables the runtime limits validation logic.

YAML

While CIOLimits is a helper class, its configuration is exposed through protocol-specific or IO-specific configuration items. In YAML, this is often represented by min, max, and step fields:

ios:
  - id: analog_output
    type: dac
    config:
      device: 0
      min: [0]
      max: [4095]
      step: [1]

Doxygen

dawn::CIOLimits