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Arm Cortex-A55 Core Technical Reference Manual : RAS error types

RAS error types

For a standard error record, three error types can be recorded.

When a processing element accesses memory or other state, errors might be detected in that memory or state, and corrected, deferred, or signaled to the processing element as a detected error. The component that detects an error is called a node.

Corrected error (CE)An error was detected and corrected. It no longer infects the state of the node and has not been silently propagated. The node continues to operate.
Deferred error (DE)An error was detected, was not corrected, and was deferred. The error is not silently propagated and may be latent in the system. The node continues to operate.
Uncorrected Error (UC)An error was detected and was not corrected or deferred. The error is latent in the system.

Note

Uncorrected errors can have subtypes depending on whether the error was produced or consumed at the node.

Errors produced at the node

For uncorrected errors that are produced at the node, the subtypes, in increasing severity, are:

LatentThe error has not been propagated. That is, the error was detected but not consumed, and was not recorded as a deferred error.
SignaledThe error has not been silently propagated. The error has been or might have been consumed, and was not recorded as a deferred error.

Note

The producer cannot know if a consumer has architecturally consumed the error. If it has definitely not been propagated to any consumer, and signaled otherwise, an error might be marked as Latent.
Unrecoverable (UEU)The error has not been silently propagated. The node cannot continue operating.
Uncontainable (UC)The error might have been silently propagated. If the error cannot be isolated, the system must be shut down to avoid catastrophic failure.

Errors consumed at the node

For uncorrected errors that are consumed at the node, the subtypes, in increasing severity, are:

Restartable (UEO)The error has not been silently propagated. The node halts operation because of consuming an error. The node does not rely on the corrupted data so can continue to operate without repairing the error.
Recoverable (UER)The error has not been silently propagated. The node halts operation. To continue, the node relies on consuming the corrupted data. If software can locate and repair the error, the halted operation can continue.
Unrecoverable (UEU)The error has not been silently propagated. The node halts operation and cannot resume from its halted state.
Uncontainable (UC)The error might have been silently propagated. If the error cannot be isolated, the system must be shut down to avoid catastrophic failure.

Error status priority

The highest priority recorded error type is recorded in the Error Record Primary Syndrome Register.