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Logic Aware Dynamic X-bounding for Better At-speed Test Coverage

IP.com Disclosure Number: IPCOM000241664D
Publication Date: 2015-May-20
Document File: 4 page(s) / 302K

Publishing Venue

The IP.com Prior Art Database

Abstract

Paths with timing exceptions like timing paths are either not timed or timed in multi-cycles functionally, (such as false_path/multicycle_path) pose a challenge for at-speed testing. LBIST (Logic Built in Self-Test) and ATPG at-speed testing techniques have test clock frequencies close or equal to the functional frequencies. Thus, timing paths with exceptions will lead to x-propagation, so effort needs to be made to mask these. This is in turn has an impact on at-speed coverage. Many applications like safety and auto, where high at-speed coverage is of great importance, are impacted. X-bounding is a technique used to mask these X propagation. This paper discusses some of the shortcomings of current x-bounding techniques and suggests a solution for the same. Exceptions: MCP: Multicycle Path, FP: False Path

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Logic Aware Dynamic X-bounding for Better At-speed Test Coverage

Paths with timing exceptions like timing paths are either not timed or timed in multi-cycles functionally, (such as false_path/multicycle_path) pose a challenge for at-speed testing.  LBIST (Logic Built in Self-Test) and ATPG at-speed testing techniques have test clock frequencies close or equal to the functional frequencies.  Thus, timing paths with exceptions will lead to x-propagation, so effort needs to be made to mask these.  This is in turn has an impact on at-speed coverage.  Many applications like safety and auto, where high at-speed coverage is of great importance, are impacted.  X-bounding is a technique used to mask these X propagation. This paper discusses some of the shortcomings of current x-bounding techniques and suggests a solution for the same.

Exceptions:         MCP:    Multicycle Path,                 FP:    False Path

BACKGROUND

Current techniques being used:

1.       Static  X-bounding

Figure 1 shows an MCP or FP from clock domain of F1 through node (A) to F2.

Static  X-bounding involves blocking the Path through an OR(AND) gate that will result in constant propagation of 1(0) masking the path from F1 to F2  but  will also result in blocking of valid paths with constant 1(0) propagation like from F1 to F3 resulting in loss of test coverage.

Fig 1

 

2.       Dynamic X-bounding

There exists an MCP or FP from clock domain of F1 through node (A) to F2.

Dynamic X-bounding involves blocking of the exception path i.e. F1 through (A) to F2, without blocking the coverage for F1 to F3 path. This is done by the use of a scan flop for F2.

 Flop FX in state-1 (Figure 2):  It will cause the blockage of path from F1 to F2 and F1 to F3.But paths from other flops to F2 can get covered as F2 will be able to capture data in this scenario.

 
 

Fig 2

 
 

Flop FX in state-0 (Figure 3):  It will cause the blockage of any path from any flop to F2.Rest all the paths will be covered from F1, Ex- F1 to F3.

Fig 3

 

The above x-bounding techniques have been...