Abstract: For a typical design there may be some design corners where ATPG tool/algorithm may find hard to generate patterns for fault detection. This leads to loss of coverage or increase in pattern count. To overcome this issue EDA tools(DFT/ATPG) provide options to insert Control logic on locations/nodes with poor controllability or Observe test logic on locations/nodes with poor observability, these are referred as Test Points. ATPG tools suggest Automatic Test Point (control/observe) along with insertion locations pertaining to following goals:
- Coverage improvement
- Pattern count reduction
Following are the two flows generally used for generating Automatic Test Points:
- Automatic Test Point Generation at DFT insertion stage
- Automatic Test Point Generation at ATPG stage
In both of the above cases the outcome will be a file having Test Point type and location where it has to be inserted (along with other relevant information dependent on tool eg. probable equivalent coverage improvement once the Test Point is inserted, number of faults targeted etc.). This file can be used by DFT insertion tool to insert suggested Automatic Test Points.
Challenge: All the three major EDA vendors provide DFT/ATPG tools, though one major issue in the above flow is that designers use DFT insertion tool from one EDA vendor and ATPG tool from other. So Automatic Test Point file generated from one EDA tool cannot be used as is by DFT insertion tool from other EDA vendor.
Organization of paper: This paper will first discuss different type of Test Points offered by EDA vendors followed by automatic Test Point file and their formats. Finally, a solution to the challenge will be discussed followed by conclusion.
The control and observe Test Points offered by EDA vendors have different logical architecture (refer user guide of respective tool for further information on this). Following are the different types of Test points offered by major EDA vendors:
Control Test Points:
Tessent supported Control test Point: It is provides two types of control points:-
- AND Control Point:
- OR Control Point:
Control points are not going to change at capture cycles. The tool does not insert the AND and an OR control points in a same net, since these points are mutually exclusive.