Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 7/19/2024
Public
Document Table of Contents

3.5.3.11. Cache Protection

The Cortex* -A76 core implements the reliability, availability, and serviceability (RAS) extension to the Arm* v8-A architecture which provides mechanisms for standardized reporting of the errors that are generated by cache protection mechanisms.
The RAS extension improves the system by reducing unplanned outages:
  • Transient errors can be detected and corrected before they cause application or system failure.
  • Failing components can be identified and replaced.
  • Failure can be predicted ahead of time to allow replacement during planned maintenance.
The Cortex* -A76 core protects against errors that result in a RAM bitcell holding the incorrect value.
The RAMs have the following capability:
  • Single error detect (SED):
    • One bit of parity is applicable to the entire word.
    • Double bit errors are not detected or corrected.
  • Interleaved parity:
    • One bit of parity is applicable to the even bits of the word, and one bit of parity is applicable to the odd bits of the word.
  • Single error correct, double error detect (SECDED)
Table 42.  Cache Protection Behavior
RAM Protection Type Protection Granule Correction Behavior
L1 instruction cache tag 1 parity bit 31 bits The line that contains the error is invalidated from the L1 instruction cache and fetched again from the subsequent memory system.
L1 instruction cache data SED 72 bits The line that contains the error is invalidated from the L1 instruction cache and fetched again from the subsequent memory system.
L1 data cache tag SECDED 34 bits + 7 bits for ECC attached to the word The cache line that contains the error gets evicted, corrected in line and refilled to the core.
L1 data cache data SECDED 32 bits of data + 1 poison bit + 7 bits for ECC attached to the word The cache line that contains the error gets evicted, corrected in line and refilled to the core.
MMU translation cache 2 interleaved parity bits 67 bits Entry invalidated, new pagewalk started to refetch it.
L2 cache tag SECDED 7 ECC bits for 37 tag bits Tag is corrected inline.
L2 cache data SECDED 8 ECC bits for 64 data bits Data is corrected inline.
L2 TQ data SECDED 8 ECC bits for 64 data bits Data is corrected inline.