| description |
This paper presents an integrated approach for both built-in online
and offline testing of embedded DRAMs. It is based on a new
technique for output data compression which offers the same benefits
as signature analysis during offline test, but also supports
efficient online consistency checking. The initial fault-free memory
contents are compressed to a reference characteristic and compared
to test characteristics periodically. The reference characteristic
depends on the memory contents, but unlike similar characteristics
based on signature analysis, it can be easily updated concurrently
with WRITE operations. This way, changes in memory do not require a
time consuming recomputation. The respective test characteristics
can be efficiently computed during the periodic refresh operations
of the dynamic RAM. Experiments show that the proposed technique
significantly reduces the time between the occurrence of an error
and its detection (error detection latency). Compared to error
detecting codes (EDC) it also achieves a significantly higher error
coverage at lower hardware costs. Therefore, it perfectly
complements standard online checking approaches relying on EDC,
where the concurrent detection of certain types of errors is
guaranteed, but only during READ operations accessing the erroneous
data.
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