culvert 0.2.0

Typed access to the HDMI 2.1 SCDC register map
Documentation 
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//! Error types returned by [`crate::Scdc`] operations.

/// Errors returned by [`Scdc`](crate::Scdc) register operations.
///
/// Two categories of failure are distinguished so that callers can handle them
/// separately: a transport failure means the I²C/DDC bus returned an error; a protocol
/// error means culvert refused the operation because it would break the SCDC protocol
/// (for example FFE levels the rate prohibits), before anything was written.
#[non_exhaustive]
#[derive(Debug)]
pub enum ScdcError<E> {
    /// The underlying transport returned an error.
    Transport(E),
    /// The operation would violate the SCDC protocol; nothing was written.
    Protocol(ProtocolError),
}

/// What culvert refuses because it would violate the SCDC protocol.
///
/// Every value a sink can report decodes (an undefined link training request is
/// [`LtpReq::Reserved`](crate::LtpReq::Reserved)), so these come from requests, not from
/// register content.
#[non_exhaustive]
#[derive(Debug)]
pub enum ProtocolError {
    /// The sink reported an FRL rate value not defined by the HDMI 2.1 specification.
    ///
    /// The inner value is the raw 4-bit field read directly from the SCDC register. It is
    /// exposed so callers can log or diagnose misbehaving sinks, not because it carries
    /// semantic meaning — any value outside the spec-defined set is treated as a protocol
    /// violation regardless of its numeric value.
    ///
    /// Not currently returned: no culvert method reads an FRL rate back from the sink.
    UnknownFrlRate(u8),
    /// The requested FFE levels exceed the maximum allowed at the requested FRL rate
    /// (see [`FfeLevels::max_for`](crate::FfeLevels::max_for)). A sink treats a
    /// prohibited value as 0, so it is rejected before anything is written.
    FfeLevelsOutOfRange {
        /// The requested FRL rate.
        rate: crate::FrlRate,
        /// The requested FFE levels.
        levels: u8,
    },
}