Niagara2 has several DFT features to aid testing and debug.
Since almost all the physical I/Os on Niagara2 consist of
SerDes, functional testing of the Core presents several challenges.
For one, SerDes link speeds are higher than what
most standard testers can handle. Also, standard testers lack
the intelligence required for SerDes protocol-level testing.
Regular shmoos fail due to the inherent in-determinism caused
by unknown phase alignment of the SerDes. A deterministic
test mode (DTM) was added in Niagara2 specifically to solve
this problem. In addition, Niagara2 has a dedicated debug
port (168-pin non-SerDes-based I/Os) which has the ability
to monitor various on-chip signals to help testing and debug.
All except a few flops in Niagara2 are connected in 1 of 32
scan chains to enable ATPG and SCAN testing. All RAM and
CAM arrays in Niagara2 are testable using MBIST and Direct Memory Observe (DMO) using Macrotest. DMO reduces test
time by enabling fast bit-mapping required for array repair. The
Transition Test technique is used for speed testing of targeted
critical paths. SERDES designs incorporate external, internal,
and pad loopback capabilities to enable their testing. Architecture
design enables use of 8 SPCs and/or L2 cache banks.
This has proved to be a valuable feature for Niagara2 because
it has shortened our debug cycle by making partially functional
die usable. It will also provide an additional advantage of
increasing overall yield by enabling partial core products.