1 research outputs found
Bit-Exact ECC Recovery (BEER): Determining DRAM On-Die ECC Functions by Exploiting DRAM Data Retention Characteristics
Increasing single-cell DRAM error rates have pushed DRAM manufacturers to
adopt on-die error-correction coding (ECC), which operates entirely within a
DRAM chip to improve factory yield. The on-die ECC function and its effects on
DRAM reliability are considered trade secrets, so only the manufacturer knows
precisely how on-die ECC alters the externally-visible reliability
characteristics. Consequently, on-die ECC obstructs third-party DRAM customers
(e.g., test engineers, experimental researchers), who typically design, test,
and validate systems based on these characteristics.
To give third parties insight into precisely how on-die ECC transforms DRAM
error patterns during error correction, we introduce Bit-Exact ECC Recovery
(BEER), a new methodology for determining the full DRAM on-die ECC function
(i.e., its parity-check matrix) without hardware tools, prerequisite knowledge
about the DRAM chip or on-die ECC mechanism, or access to ECC metadata (e.g.,
error syndromes, parity information). BEER exploits the key insight that
non-intrusively inducing data-retention errors with carefully-crafted test
patterns reveals behavior that is unique to a specific ECC function.
We use BEER to identify the ECC functions of 80 real LPDDR4 DRAM chips with
on-die ECC from three major DRAM manufacturers. We evaluate BEER's correctness
in simulation and performance on a real system to show that BEER is effective
and practical across a wide range of on-die ECC functions. To demonstrate
BEER's value, we propose and discuss several ways that third parties can use
BEER to improve their design and testing practices. As a concrete example, we
introduce and evaluate BEEP, the first error profiling methodology that uses
the known on-die ECC function to recover the number and bit-exact locations of
unobservable raw bit errors responsible for observable post-correction errors.Comment: To appear in the MICRO 2020 conference proceeding